ISS Lectures Astrobiology

8/14/2019 ISS Lectures Astrobiology

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12-25 July 2009

Edited by Adam Selinger and Anne Green

The lecture series o the35th Proessor Harry MesselInternational Science School

The Science Foundation or Physics withinthe University o Sydney

In the Pursuit o Excellence


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EditorsMr Adam Selinger, Executive Ocer

Proessor Anne Green, DirectorThe Science Foundation or Physics within The University o Sydney, Australia

A course o lectures given at the 35th Proessor Harry Messel International Science School or HighSchool Students organised by the Science Foundation or Physics within The University o Sydney

1225 July 2009

There are several people to thank or the production o this book o lectures. Firstly thanks to all oour contributors, who have given their time to the ISS and have been generous in providing a chap-ter or each o their lectures; to Proessors Bob Hewitt and Dick Hunstead and Dr John OByrne ortheir proo-reading o the pages within, and to the design team at University Publishing Service.

The Science Foundation or PhysicsSchool o Physics A28The University o Sydney NSW 2006 Australiawww.physics.usyd.edu.au/oundation

Copyright Science Foundation or Physics June 2009All rights reserved. No part o this publication may be reproduced, stored in a retrieval systemor transmitted in any orm or by any means, electronic, electrostatic, magnetic tape, mechanical,photocopying, recording or otherwise, without permission in writing rom the Science Foundationor Physics, The University o Sydney.

Designed and printed by the University Publishing Service, the University o Sydney.Genes to GalaxiesISBN: 978-0-9599471-2-0


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Contents

The Messel Endowment 5

Supporters of ISS2009 8

Preface 9

History of the ISS 10

Authors 12

The search for the earliest life on EarthMalcolm Walter 14

The search for life on MarsMalcolm Walter 20

Paleolithic nutrition: what did our ancestors eat? Jennie Brand Miller, Neil Mann and Loren Cordain 28

A Walk Around the Neighbourhood:Understanding the Nature and Structure of the Milky WayNaomi M McClure-Grifths 44

Gene Silencing I A virus defence pathway and a technologyPeter Waterhouse 56

Dr Karl: The X-Chromosome eXplained 66

The frontiers of current biological research

Michel Morange 74Why is it important to read On the Origin of Species in 2009?Michel Morange 84

Cosmic Evolution: The Birth, Life & Death of GalaxiesGeraint F Lewis 92

Gene Silencing II Gene regulationPeter Waterhouse 106

SETI - Planning for Success:Who Will Speak to Earth? What Will They Say?

Jill Tarter 114

Six Minute of TerrorWayne Lee 126

Dr Karl: Man on Moon Conspiracy 138

Extremophiles & Exoplanets Jill Tarter 144

New Stars in NASAs ConstellationWayne Lee & Erisa K Hines 156


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The Messel Endowment

To ensure the continuation o the Proessor Harry Messel International Science School the ScienceFoundation or Physics established The Messel Endowment in 1999.

From 2003 to 2006 an active capital campaign or The Messel Endowment, chaired by Mr JohnHooke CBE, raised around $2.9Million. Currently the Endowment holds over $3.1Million. Thegoal is to accrue a total o $5Million through gits and grants to ensure the ISS can be run in perpe-tuity, whilst allowing or rising costs over the years.

The Messel Endowment is open to accept donations at any time and currently has over 200 sup-porters. Donations o $2.00 and over are tax-deductible (to Australian residents). Pledged gits (i.e.donations spread over a three to ve year period) are also accepted and are tax deductible.

The ISS now has over 4,000 alumni, with many going on to outstanding achievements in theirchosen elds, including science, medicine, engineering and technology. The ISS honours excellencein our high-achieving youth. It encourages them to reach their ull potential and pursue careers inscience and its related areas.

A donation to The Messel Endowment is an investment in the uture o these young scientists. Adonation orm can be ound at the back o this book and at www.physics.usyd.edu.au/oundation.

Extra Galactic Donors $1Million and overDepartment o Innovation, Industry, Science and Research

Mr Ming Tee Lee & Mulpha Australia Limited

Galactic Donors $100,000 to $999,999Hermon Slade Foundation

Nell & Hermon Slade Trust

Science Foundation or Physics

Stellar Donors $10,000 to $99,999ANZ Banking Group Ltd

Mr Terrey P Arcus

Mr Robert Arnott

Australian Business Limited

Emeritus Proessor Maxwell H Brennan AO

& Mrs Ionie M Brennan

Dr Gregory Clark

Cochlear Limited

Emeritus Proessor Richard Collins

& Mrs Marilyn Collins

Mr Trevor Danos

Cecil & Ida Green Foundation

Associate Proessor Robert G Hewitt

& Mrs Helen HewittMr John A L Hooke CBE

IBM Australia Limited

James Hardie Industries Pty Ltd

Dr Peter Jones

Macquarie Charitable Foundation Limited

Emeritus Proessor Harry Messel AC CBE

Mr Michael Messel

Mr Jim OConnor

OneSteel Limited

Queensland Cyber InrastructureFoundation Limited

The James N Kirby Foundation Pty Limited

USA Foundation

Westpac Banking Corporation

Mr Albert YL WongMr Thomas Yim


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6|Genes to Galaxies

Planetary Donors $1,000 to $9,999Mr Fraser Allan

Anonymous

ASA ITF Foundation or the Advancement oAstronomy

Dr Joseph A Beunen

Dr Kenneth Coles AM & Ms Rowena Danzigerthrough the Kenneth Coles Foundation

Proessor Lawrence E Cram

Mr David C Davidson

Emeritus Proessor John Davis

Mrs Georgina Donaldson

Ms Jane Dyson

Mr Steven K Eckowitz

Dr Robert Every

Dr Robin B FitzsimonsMr David Frecker

Proessor Anne Green

Mr Graham H Hall

Mr David Herrman & Mrs Hillda Herrman

Mr Anthony Johnston

Lahili Pty Limited

Mr Reginald J Lamble AO

Ms Danielle M Landy

Dr David Malin

Mrs Kathy Manettas

Mr Nicholas Manettas

Mr Peter Manettas AM

Dr Bruce McAdam & Mrs Janice McAdam

Dr Jenny Nicholls

Dr Brian J OBrien

Dr Stephen D Segal

Mr Basil Sellers AM

Dr Emery Severin & Mrs Sharman Severin

Southcorp Limited

Ms Valma G StewardMr John A Vipond

Mr Christopher C Vonwiller

Mr Raymond Walton & Mrs Margit Walton

Mr Thomas M F Yim on behal o Alex Yim

Asteroidal Donors Upwards to $999

Mr Arun AbeyMs Hyacinth Alonso

Ms Belinda H Allen

Dr Kevin C Allman

Ms Jenny Allum

Mrs Chrissie Athis

Mr George Athis

Barker College

Mrs Helen Bell

Emeritus Proessor Louis C Birch

Dr David G Blair

Sir Walter Bodmer

Ms Elana Bont

Dr George F Brand

Mr John Bright and Ms Karen Palmer

Mr Arthur J Buchan

Mr Je Close

Dr Claire E Cupitt

Mr Ian G Dennis

Ms Margaret A DesgrandMrs Iona S Dougherty

Mr Julian J DrydenMr Ian A Dyson

Ms Julie K Ellinas

Proessor David R Fraser

Mrs Irene P Gibson

Mr Greg and Mrs Gabriella Howard

Mr Sang Huynh

Mr Steven Kambouris

Dr Toni R Kesby

Ms Tomoko Kikuchi

Mrs R Lambert

Mr Wen W Ma

Dr Robert H Masterman

Dr John E.W. Lambert-Smith

Associate Proessor Donald D Millar

Mr Alan K Milston OAM

Miss Mary Moore

Ms Alison Muir

Dr Hugh S Murdoch

Mr Robert R B Murphy

Mr Spiro J Pandelakis


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ISS 2009|7

Mr Frank Papadopoulos

& Mrs June Papadopoulos

Mr George Papadopoulos

Mr John Paterson

Mr Harry J Pemble

Mr Peter C Perry

Dr Christopher J E Phillips

Mr Enrico Piccioli

Ms Yvonne Pitsikas

Mr Georey D Pople

Mr Allan F Rainbird

Mr John W L Rawson

Dr David Z Robinson

Miss Gracie Robinson

Dr P E Rolan

Proessor Roger Short

Dr J. E.W. L. Smith

Mr Tim M Smyth

Mr Duncan Sutherland

The Australian Association o Phi Beta Kappa

The Outsiders Club o ISS2007

The Super Secret Club o ISS2005

Mr Gavin M Thomson

Dr Jennier J Turner

Mr John H Valder

Ms Alex Viglienzone

Ms Jennier H F Wanless

Dr David R V Wood

Ms Anne Woods

Mr Thomas M F Yim on behal o Jerome Yim

Dr Xian Zhou

Fr Mervyn J F Ziesing

School o PhysicsBuildingImage:Dr Phil Dooley


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8|Genes to Galaxies

Supporters o ISS2009

The Science Foundation or Physics warmly thanks the supporters o the2009 ISS: Genes to Galaxies

The Messel EndowmentDepartment o Education and Training, NSW Government (DET)

Department o Innovation, Industry, Science and Research, Australian Government (DIISR)

The Kirby Foundation

Adolph Basser Trust

Faculty o Science, The University o Sydney

Chancellors Committee, The University o Sydney

The Smithsonian Institute

Mr Robert Arnott

Mr Greg Clark

Mr Trevor Danos

Mr Ron Enestrom

Associate Proessor Robert Hewitt & Mrs Helen Hewitt

Mr John Hooke CBE

Associate Proessor Brian James & Dr Ferg Brand through Dr Wie Xu

Dame Leonie Kramer

Mr Bruce McAdam & Mrs Janice McAdam

Mr Robert Rich

Mr Albert Wong

other individuals through the Foundations Annual Appeal

Australian students were selected with the support o the NSW Department o Education andTraining, and Science Teachers Associations in Victoria, Tasmania, South Australia, the NorthernTerritory, the ACT and Western Australia. The ollowing institutions assisted in the selection andtravel o the overseas students:

The Aliated High School o Peking University, China

Rivers Collegiate, Canada

Ministry o Education, Culture, Sports, Science and Technology (MEXT), Japan

Ministry o Education, Malaysia

The Royal Society o New Zealand

Ministry o Education, Singapore

Ministry o Education, Thailand

The Association or Science Education, UK

The Royal Institution o Great Britain

The National Endowment or Science, Technology and the Arts (NESTA), UK

Department o Energy, USA

Raman Research Institute, India


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ISS 2009|9

Professor Anne GreenSydney, June 2009

The presence o some 144 gited young peoplerom many countries creates an environment inwhich each scholar can experience the values o

dierent cultures and learn new ways o doingthings. The Science Foundation stands or thePursuit o Excellence, and is pleased to have anopportunity to acknowledge and reward excel-lence in these young people.

The International Science School can only beheld because o the generous nancial contri-butions into The Messel Endowment and tothe ISS rom our supporters, and because othe time and energy donated by the lecturers.Like the Science Foundation itsel, the sup-porters, donors and lecturers are committedto promoting science education at the veryhighest level o excellence. On behal o theFoundation, I express my grateul thanks to allthese beneactors.

To our scholars this year, I wish you a mostenriching ortnight here at the University oSydney and trust that you, like those beoreyou, will enjoy a remarkable and memorableexperience, make many lie-long riends andeel empowered to pursue your passion orscience.

With very warm wishes

Preace

The Science Foundation or Physics within theUniversity o Sydney is delighted to presentthe 35th Proessor Harry Messel International

Science School (ISS) or high school students,rom 12-25 July 2009.

This anniversary year is the UN-designatedInternational Year o Astronomy and celebratesboth 400 years since Galileo rst turned histelescope to the heavens and the 150th anni-versary o the publication o Charles Darwinstreatise On the Origin o Species. Thereorethe theme or ISS2009 is Genes to Galaxies,acknowledging the immense contributionmade to science by these two great minds. Thesecond week o the ISS also coincides withthe 40th anniversary o the rst landing onthe moon by Apollo 11 astronauts. It bringstogether our themes o evolution and spaceexploration, with speculation o possible intel-ligent lie beyond the Earth.

The primary aim o all the Science Schools is toacknowledge the excellence o the scholars whohave been selected on the basis o their aca-demic abilities, passion or science and leader-ship qualities. A new initiative or this ISS is theintroduction o a module on Leadership andEthics in Science, produced with the supporto the Smithsonian Institute and introducedduring the opening lecture by the Chie Justiceo Australia, the Honourable Robert French,himsel an ISS alumnus.


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10|Genes to Galaxies

The Proessor Harry Messel InternationalScience School has a long and distinguishedhistory. The 144 students attending ISS2009:

Genes to Galaxies are the 35th group to gatherat the University o Sydney or the ScienceSchool in all, well over 4000 have attended aScience School since they began in 1958.

Initially the Schools were annual events, andthe rst our Schools, held between 1958 and1961, were or teachers. In 1962 ProessorHarry Messel, the ounder o the ISS, changedthe ocus to honour excellence in senior highschool students and to encourage them to con-sider careers in science.

A Truly InternationalScience School

One student rom New Zealand attended thevery rst Science School in 1962, and overseasstudents have been a eature o the ISS eversince. In 1967, ten students travelled romthe USA to attend the School; the ollowing

year they were joined by ve rom the UnitedKingdom and ve rom Japan.

South-East Asia joined the ISS in 1985 whenstudents attended rom Singapore, Malaysia,Thailand and the Philippines however, thatwas the only time the Philippines has partici-pated. China has sent ve students to every ISSsince 1999, except or 2003 when the SARSepidemic restricted travel in the region andthey reluctantly withdrew. In 2007 we were un-

ortunate not to be joined by Malaysia but wedid welcome India or the rst time.

This year we are very pleased that or therst time we will be joined by students romCanada, in act rom the home town o HarryMessel, the originator o this program. ThusISS2009 has students attending rom tencountries in total: Canada, China, India, Japan,Malaysia, New Zealand, Singapore, Thailand,the UK and the USA, and o course, every state

and territory o Australia.

The Great Lecturers

One o the eatures o the International Science

Schools is the lecture series. Past ISS lectur-ers include James Watson, who won a NobelPrize or discovering the structure o DNA,and Jerome Friedman, also a Nobel laureateor work on particle physics. Sir HermannBondi (physicist and astronomer at CambridgeUniversity), Margaret Burbidge (astronomerand champion or women in science), CarlSagan (amous astronomer and science broad-caster) and Lord Robert May (President o theRoyal Society in the UK) have all given talks atthe ISS.

And o course, who could orget the brilliantscience demonstrations o Proessor JuliusWhy is it so? Sumner Miller, which weresuch a popular eature o the ISS that theyspawned a television show! These days, Dr KarlKruszelnicki (the Universitys Julius SumnerMiller Fellow) entertains and enthuses the ISSScholars with his amous Great Moments in

Science.Between 1960 and 1979 the ISS lectures wereshown on television in act, many people re-call waking up early on Sundays to make surethey didnt miss the telecast! One member othe School o Physics here at the University oSydney is adamant that the lectures shown onTV were a key part o her decision to becomean astronomer.

Today, the ISS is no longer a eature o the

television schedule, but we have moved on toembrace new technology. In 2003 part o thelecture series was broadcast on the internet asa trial run, and in 2007 the entire series wasmade available as both video webcast and au-dio podcast. In 2009 this book o lectures willbe made available on-line, together with pod-casts o the lectures, thus available to anyonewith internet access on Earth, and beyond.

History o the ISS


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ISS 2009|11

Science School 1958-2007

For High School Teachers

Year Teachers Theme

1958 123Selected Lectures in Modern Physics and the

Astronomers Universe

1959 123Lecture notes on an introductory course in modern

physics and nuclear power and radioisotopes

1960 123 From Nucleus to Universe

1961 123 Space and the Atom

TOTAL 492

International Science Schools For High School Students

Year Boys Girls Total Theme

1962 108 45 153 A Journey through Space and the Atom

1963 104 51 155 The Universe o Time and Space1964 106 53 159 Light and Lie in the Universe

1965 114 42 156 Time (and Relativity)

1966 104 52 156 Atoms to Andromeda

1967 101 57 158 Apollo and the Universe

1968 109 20 129 Man in Inner and Outer Space

1969 118 21 139 Nuclear Energy Today and Tomorrow

1970 99 33 132 Pioneering in Outer Space

1971 87 35 122 Molecules to Man

1972 95 28 123 Brain Mechanisms and the Control o Behaviour

1973 93 29 122 Focus on the Stars1974 90 33 123 Solar Energy

1975 76 43 119 Our Earth

1977 54 50 104 Australian Animals and their Environment

1979 63 52 115 Energy or Survival

1981 50 65 115 Biological Manipulation o Lie

1983 67 51 118 Science Update 1983

1985 71 59 130 The Study o Populations

1987 70 56 126 Highlights in Science

1989 69 58 127 Todays Science Tomorrows Technology

1991 61 70 131 Living with the Environment1993 60 72 132 Carbon: Element o Energy and Lie

1995 55 80 135 Breakthrough! Creativity & Progress in Science

1997 72 65 137 Light

1999 73 66 139 Millennium Science

2001 70 71 141 Impact Science

2003 54 85 139 From Zero to Innity

2005 73 66 139 Waves o the Future

2007 68 65 133 Ecoscience

TOTALS 2434 1573 4007


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Associate Proessor Alaina Ammit is AssociateDean (Research & Innovation) at the Faculty oPharmacy, University o Sydney. She has earned aninternational reputation or her work elucidatingpro-infammatory signalling pathways in asthma andairway remodelling.

Authors

Proessor Jennie Brand-Miller holds a Personal

Chair in Human Nutrition in the Human Nutrition Unit,School o Molecular and Microbial Biosciences at theUniversity o Sydney. She is internationally recognisedor her work on carbohydrates and diabetes, particularlythe glycemic index o oods.

Dr Helen Johnston obtained her PhD at the CaliorniaInstitute o Technology. Subsequently she obtained post-doctoral appointments in The Netherlands, at the Anglo-

Australian Observatory and at the University o Sydney.Her research interests are the study o neutron stars andblack holes in binary star systems, and thesupermassive black holes at the centres o radio galaxies.

Mr Wayne Lee is Altair Vehicle Systems Managerat NASA. Previously Wayne enjoyed great success asthe mission planner or Mars operations at NASAs JetPropulsion Laboratory in Pasadena, Caliornia. During

the mission, Wayne worked with all the elements o thefight team to coordinate trajectories, science plans andspacecrat operations into the overall mission itinerary.

Proessor Geraint Lewis was born in Old SouthWales, and studied Physics at London University andCambridge. Since completing his PhD he has workedin the State University o New York, Victoria Universityin Canada, and the University o Washington in Seattle.He then became a Research Astronomer at the Anglo-

Australian Observatory beore joining The University oSydney in 2002 to continue his studies o cosmology.


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Authors|13

Associate Proessor Charles H. Lineweaver isthe coordinator o the Australian National UniversitysPlanetary Science Institute and holds a joint appoint-ment as an Associate Proessor in the Research School oAstronomy and Astrophysics and the Research School oEarth Sciences.

Proessor Michel Morange was trained in biochemis-

try and molecular biology at the Pasteur Institute in Paris.He then turned to cell biology, and entered into FranoisJacobs lab in the same Institute. With Olivier Bensaude, hecreated in 1991, at the Ecole normale suprieure in Paris,a group whose project was to characterise the regulation oheat shock gene expression.

Dr Naomi McClure-Grifths is a Senior Post-DoctoralFellow at the CSIRO Australia Telescope National Facility.Her research has dramatically reshaped our knowledgeo the structure and evolution o our galactic home theMilky Way.

Proessor Jill Tarter holds the Bernard M. Oliver Chairor SETI (Search or Extraterrestrial Intelligence) andis Director o the Center or SETI Research at the SETIInstitute in Mountain View, Caliornia. Jill is popularlyknown or being portrayed by Jodie Foster in the lmContact.

Proessor Malcolm Walter is Proessor o Astrobiologyat the University o NSW and Director o the AustralianCentre or Astrobiology based there. He has worked or 45years on the geological evidence o early lie on Earth, and

more recently on the search or lie on Mars. He has alsoworked as an oil exploration consultant and a consultantto museums.

Proessor Peter Waterhouse is internationally recog-nised or his groundbreaking research on plant viruses. Heled the way in uncovering the mechanism, roles and ap-plications o post-transcriptional gene silencing in plants,also termed RNA intererence (RNAi).


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The record o lie on Earth takestwo orms: ossils and other evi-

dence in the geological record,and what is encoded in the ge-

nomes o living organisms.

The rock record limitations

What we can learn rom rocks diminishes backthrough time. The urther we go back in time,the ewer the rocks preserved. That is becauseo natural recycling processes: rocks weather,turn to sediment that is washed into seas andlakes, get buried by more sediment, and getsubducted and melted during tectonism(continental drit). The result is there are noknown well-preserved rocks older than 3.5billion years (Ga) old. The Earth is 4.56 Ga old(Figure 1). So we dont know much about therst billion years o Earth history. Lie aroseduring that time. We know that because wehave ossils 3.5 Ga old rom Western Australia.

Even at 3.5 Ga there are only two knownregions o rock preserved, the Pilbara regiono Western Australia, and the BarbertonMountainland o South Arica.


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From about 3 Ga onwards we have lots o rocksto examine or evidence o lie, so we can bemore condent about our interpretations.

Events in the history o lie are dated mostlyusing the act that some isotopes o elementsare unstable and break down at known rates toorm other isotopes and elements. The usualmethod o dating very ancient rocks uses ura-

nium and lead isotopes bound in crystals ozircon, zirconium silicate.

Universal tree o lie

There is a second way to uncover the earliesthistory o lie. That history is encoded in thegenes o living organisms. Using the subtledierences in the chemistry o the genetic mol-ecules DNA and RNA molecular biologistshave been able to work out the relationships oall current lie on Earth. The result is a chart orelationships, one o the greatest achievementso science in the last 100 years.

Lie clusters into three great superkingdomsor domains, the Bacteria, Archaea andEucarya (Figure 2). From this we can see thatmost lie on Earth is microscopic. This is con-sistent with the geological record that shows usthat until about 600 Ma almost all ossils are

o microbes.

The universal tree also suggests that the mostprimitive organisms with living close relativeswere hyperthermophiles, that is, they lived athigh temperatures, more than 80C. So in theancient rock record we should be looking orthe deposits o ormer hot springs to see whatlived in them. We know how to nd suchdeposits they are oten ores o gold, silver,

copper, lead and zinc.

Figure 1:Geological timedisplayed as a

clock, in billions oyears. Major eventsin the evolution olie are indicated.Reproduced romDes Marais, D.J.(2000) When DidPhotosynthesis emergeon Earth? Science 289:1703-1705 with thepermission o DavidDesMarais

Figure 2: The Universal Tree o Lie, achart o the relationships o all extant lie.Source: Wikimedia Commons


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The search or the earliest lie on Earth|17

Earth - The frst billion years

Like the other planets, the Earth ormed roma great cloud o dust and gas. Under the infu-ence o gravity the cloud clumped into rocky

and icy lumps that grew bigger and bigger. Thevolatile molecules were driven to the coolerurther parts o the solar system as the Sun be-gan to generate heat, orming the gas giants,Jupiter, Saturn, Uranus and Neptune, the com-ets, and other objects such as Pluto. The smallrocky planets, composed o less volatile mate-rial, Mercury, Venus, Earth and Mars, ormedclose to the Sun. By 4.56 Ga they were abouttheir present size. However, or the next billion

years the growth process, accretion, contin-ued and was very violent. Soon ater 4.56 Gaan object the size o Mars smashed into theEarth with such energy as to melt and vapor-ise the surace o the planet, throwing a vastamount o material into orbit, which cooled toorm the Moon. Frequent impacts rom giantasteroids continued until about 3.9 Ga. Someo these would have vaporised the developingoceans, generating a steam atmosphere. Liemight have started in this violent period buthave been extinguished. We do not know.

Imagine an Earth with thousands o volcanos,no continents but perhaps numerous islandsthat would later clump together to becomecontinents, and a hot ocean. Somewhere liegot started and managed to survive, prolierateand take over to generate the surace environ-ment we now depend on or our existence.Faint evidence o the presence o lie is ound

in highly altered 3.9 Ga rocks rom Greenland.There are no conventional ossils, just sugges-tive patterns o carbon isotopes.

A snapshot at 3.5 Ga

We know rom studying the rocks o thePilbara region and the Barberton Mountainlandthat lie was well established by 3.5 Ga. Despiteoccasional controversies, the evidence can bedescribed as compelling because multiple lines

o evidence reinorce and support each other.

1 Stromatolites These are macroscopic sedi-mentary structures resulting rom the activitieso mats o microbes living on the seafoorand in lakes. They still orm in some modernenvironments such as Shark Bay in WesternAustralia (Figure 3), so we are able to observehow they orm and use this inormation to helpinterpret the ancient orms.

In 3.43 Ga rocks in the Pilbara region, a widerange o dierent orms o stromatolites (Figure

4) ormed all the way rom a rocky coastline tooshore in several tens o metres o water. In3.5 Ga rocks there are stromatolites at the ventso ormer hot springs.

2 Microfossils These are ossilised microbes(Figure 5). Despite the act that microbes haveno hard parts they are sometimes ossilisedwhen they become embedded in precipitatedsilica which then hardens to orm a rock calledchert. They can be ound by using an optical

microscope to examine slices o chert so thinthat light can pass through them.

3 Carbon isotopes Carbon has two stableisotopes, 12C and 13C. Some biochemical proc-esses such as photosynthesis preerentially usecompounds o light carbon, 12C. This resultsin the cellular matter being enriched in 12C,leaving the water in which the organisms grewenriched in 13C. I calcium carbonate thenprecipitates out o the water to orm limestone,

and the microbes die and are ossilised in the

Figure 3: Shark Bay stromatolites in theshallow subtidal environment.Malcolm Walter


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Figure 4:Stromatolites 3.43billion years oldwest o MarbleBar in the Pilbararegion o WesternAustralia.Malcolm Walter

Figure 5: Filamentous microossil 3.5billion years old rom near MarbleBar in the Pilbara region o WesternAustralia. The drawing on the right is areconstruction.Photographs courtesy o J. William Schop and

reproduced with permission.

limestone, the carbon isotope pattern is pre-served. This pattern is ound throughout Earthhistory back to 3.5 Ga and possibly to 3.8 Ga.

Complex lie at 3.0 Ga?

Recently, large and relatively complex micro-ossils have been ound in 3.0 Ga rocks in thePilbara (Figure 6). These include spheroids upto 80m wide, some with internal small sphe-

roids, and discoidal structures with fanges, likeclassical pictures o fying saucers. It is notknown what sort o organisms these were, buttheir large size and relative complexity hint thatthey might be eukaryotes.

All the hard evolutionover by 2.5 Ga

There are many well preserved rock succes-sions at 2.5-2.8 Ga and abundant evidence o

lie. All lie was still microscopic, as ar as weknow. All three domains are represented in thegeological record. Some continents had ormedand stromatolites were abundant in lakes andshallow seas. Though the evidence is not un-equivocal it is likely that the main stromatolite-builders were cyanobacteria; this is deducedrom the morphology o the stromatolites andsome poorly preserved microossils. The pres-ence o cyanobacteria at this time is strongly

indicated by another type o evidence: bi-omarkers. These are hydrocarbon moleculesthat can be ound in especially well preserved


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The search or the earliest lie on Earth|19

sediments. Oil contains abundant biomarkers.Ater organisms die, decay and are buried insediment some chemical components o their

cells survive. Some o these organic compoundsare characteristic o particular types o organ-isms, so when ound in rocks they are markersor the ormer presence o these organisms.Compounds characteristic o cyanobacteria,and others characteristic o eukaryotes havebeen ound in 2.7-2.8 Ga rocks in the Pilbararegion and in South Arica. There is somecontroversy about this work as it is dicult toprove that these molecules are not later con-

taminants, but most o the evidence indicatesthat they are as old as the rocks in which theyare ound.

So we know that by 2.5 Ga, and probablymuch earlier, all three domains o lie werefourishing on Earth. That means that mosto the biochemical processes that characterisemodern lie had evolved by that time. All sub-sequent evolution has utilised those basic proc-esses rst established by microbes.

How did lie start?

There is a simple answer to that question:no-one knows. However, there are ways to ap-proach the problem, and a great deal has beenlearned in the last 50 years. A amous experi-ment was conducted in 1952 by Stanley Miller

(then a university student in Chicago) and hissupervisor Harold Urey. They lled a glass faskwith a mixture o gases considered to representthe composition o the atmosphere on the earlyEarth methane, ammonia, hydrogen, carbonmonoxide and water. To represent lightningthey created electrical sparks through the mix-ture o gases. The result was a brown liquidthat when analysed was ound to contain ami-no acids. These are the building blocks o pro-

tein molecules that are essential componentso the cells o all living organisms. So they haddemonstrated one possible step in the origino lie. Since then it has been discovered thatthere are many other ways that quite complexcarbon compounds (organic compounds) canorm by natural chemical processes. This evenhappens in gas clouds in the universe (about100 dierent carbon compounds have beenidentied in such clouds), and so would havebeen part o the cloud that condensed to ormthe solar system.

It is a long way rom organic compounds to lieand much is yet to be learned. For example,no-one has yet been able to synthesise a pro-tein molecule, let alone the genetic moleculesRNA and DNA. But there are comprehensivehypotheses about how lie might have startedand many o the necessary steps have beenshown to be easible. Perhaps viruses played arole beore there were cells. A potentially veryinormative approach is to determine whatessential components o cells are ound in themost primitive orms o lie known, and ex-trapolate back to predict what the earliest cellswere probably like.

Figure 6: Spindle-shaped microossil atleast 3.0 billion years old rom the Pilbararegion o Western Australia. About 40 min maximum dimension.Photograph courtesy o Kenichiro Sugitani andreproduced with permission.


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The search or

lie on MarsMalcolm Walter


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It has long been thought that theremight be lie on Mars. A century ago

some astronomers thought that theycould see canals on Mars and imagined

a dying civilisation on a drying planet strug-gling to survive. In the 1950s astronomersnoticed that patches o colour on Mars changewith the seasons and thought that this mightbe due to seasonal changes in vegetation. Inthe 1960s and 70s some enthusiasts saw inthe rst uzzy pictures rom Mars pyramidsand a giant ace.

All were deceived. Modern high resolutionimages show that there are no canals, pyra-mids or aces. And the colour changes resultrom seasonal dust storms.

Why ocus on Mars?

Over the last decade more than 350 extra-solar planets have been discovered and ourown solar system has been explored in everincreasing detail. There could be lie on manyplanets and moons, though none has yet beenound, but Mars is special. That is because we


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have discovered that early in its history it waswarm and wet, like the Earth, although now itis a rozen desert (Fig. 1).

All lie on Earth requires liquid water, and sothe assumption is made that that will also betrue o lie elsewhere. Similarly, all lie on Earthis constructed rom compounds o carbon, andthis too is assumed to be true o lie elsewhere.This is just a normal conservative scientic ap-proach, o making predictions on the basis ocurrent knowledge. It does not rule out otherpossibilities, but indicates where the ocusshould lie.

The Ages o eatures on Mars

As yet no samples have been collected on Marsand returned or analysis, so we have no directdates or the eatures we observe. However,there is an indirect way o determining ap-proximate ages. Like all the rocky planets Marsaccreted rom the inall o asteroids, meteorites,comets and dust. The rate o inall, bombard-ment, was very high early in the lie o thesolar system and diminished to the current verylow rate about 3.9 billion years ago. We know a

little about rates o bombardment because sam-ples o the Moon collected during the Apollomissions have been dated here on Earth, andthose dates can be directly related to the crater-ing o the Moon. It is assumed that the rateswould have been similar on Mars.

So or Mars we can count the number o cratersin a particular region and on that basis deter-mine the approximate age o the landscape.This is how we know that the warm and wetperiod was more than three billion years ago.

Water on Mars

It has been known since the NASA Marinermissions in the 1960s that something liquidfowed on the surace o Mars early in its his-

tory. That is demonstrated by an abundanceo now-dry river valleys (Fig. 2). Liquid waternow is not stable on the surace o Mars be-cause o very low temperatures combined withlow atmospheric pressures (Fig. 3). As a result,water ice sublimes directly to vapour withoutpassing through a liquid phase. Even at thecurrent very low temperatures there is still anactive hydrological cycle. One o the Vikinglanders in 1976 observed water rost on rocks

and the Phoenix lander in 2008 observed snowalling.

A range o observations have demonstrated thatthe polar caps o Mars are a mixture o carbondioxide ice and water ice. Recent studies using

Figure 1: An image o Mars showing thenorthern polar cap. The white patches arewater-ice clouds.Image courtesy o NASA/nasaimages.org

Figure 2: Dry river valleys and meteoritecraters, imaged by Mariner 9. The imaged

area is several hundred kilometres wide.Image courtesy o NASA/nasaimages.org


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The search or lie on Mars|23

gamma ray spectroscopy and ground penetrat-ing radar observations rom satellites haveshown that water ice is very widespread on theplanet, but most is covered by sediment. Thereis evidence o glaciers.

So there is no shortage o water. There will

be liquid water at depth in the crust o Marsbecause the interior o the planet is hot. That

is known because there are volcanoes thathave been active in the last ew million years.Olympus Mons is an example (Fig. 4).

At the equator in Summer, water could beliquid within a hundred metres o the groundsurace. There is evidence that even now occa-

sionally water comes to the surace, perhaps a-ter an earthquake or a meteorite strike. NASAsorbiter Mars Global Surveyor discovered largenumbers o small gullies on the walls o me-teorite craters (Frontis piece). The gullies areresh and have not been eroded by the wind,and new ones appeared over the lietime othe mission (Fig. 5). Although it is not knownwith certainty, the most plausible explanationis that the gullies were eroded by brie outfowso liquid water rom underground aquiers.More recently, possible droplets o water werephotographed on the legs o the Phoenix landerin 2008 (Fig. 6).

Meteorites rom Mars

In 1996 NASA held a press conerence inWashington DC to announce the possiblediscovery o lie on Mars. Naturally enoughthis generated a huge amount o attention

worldwide.The discovery involved meteorite ALH84001(Fig. 7). This meteorite was discovered in the

Figure 3: A phasediagram comparingthe suraceenvironments onEarth and Mars,showing why pureliquid water can notexist on the suraceon Mars.

Image courtesy oNASA/nasaimages.org

Figure 4: The largest known volcano inthe solar system, Olympus Mons on Mars.

It is 500 km in diameter and 27 km high. IImage courtesy o NASA/nasaimages.org


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Allen Hills in Antarctica in 1984 and was therst to be catalogued that year, hence the name.Amongst the thousands o meteorites thathave been ound, 34 are known to have comerom Mars. We know that because they have adistinctive chemical and mineralogical compo-sition dierent rom any other rocks ound onthe Earth or the Moon, and dierent rom allother meteorites. Trapped within tiny bubbles

in one o these meteorites are gases that matchthe composition o the atmosphere o Mars.

It happened like this: an asteroid hit Mars andblasted surace rocks o at such a high velocity

that they could escape the gravity o Mars. Theorce o the blast melted parts o the rocks andas they few up through the atmosphere gaseswere trapped in the melt. The rocks cooled inspace, permanently trapping the gases.

Back on Earth, in a laboratory in Houston, therock was broken open and examined with anelectron microscope. Structures resemblingossil microbes were ound on the brokensuraces (Fig. 8). That discovery led to moredetailed analyses to determine whether themeteorite contained any other evidence o lie.Organic compounds called polycyclic aromatic

Figure 5: Recentlyormed gullieson the rim o animpact crater. Theseare considered

to be evidencethat occasionallyliquid water romundergroundaquiers reaches thesurace and fowsor long enough toerode these eatures.Image courtesy o NASA/nasaimages.org

Figure 6: The globules shown boxed on a leg o the Phoenix lander in 2008 are

interpreted by some scientists as water that can remain liquid because it is extremelysalty.Image courtesy o NASA/nasaimages.org


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hydrocarbons (PAHs) were ound, along withdistinctive patterns o carbon isotopes. Thisand other evidence ormed the basis or theclaim that the meteorite contained evidence othe ormer presence o lie on Mars.

Since 1996 many scientists have studiedALH84001 using a wide range o sophisticatedtechniques. The conclusion is that all o theobserved eatures can be explained by non-biological chemical processes, and none isevidence or lie. This is typical o how scienceworks: hypotheses are oered and then manyare reuted.

Methane in the Martian

atmosphereTelescopes on Earth can be used to analyse theatmosphere o Mars because dierent gaseshave characteristic inrared spectra. In 2003,patches o atmosphere rich in methane werediscovered. Three large patches, or plumes,are now known. This is signicant becausemethane is unstable on Mars and would breakdown rapidly. So there must be active sourcesspewing the methane out o the crust. This alsohappens on Earth where there are two types osources: volcanoes and microbes.

Figure 7:MeteoriteALH84001which was onceconsidered tocontain evidence olie on Mars.Image courtesy oNASA/nasaimages.org

This demonstrates that Mars is still an activeplanet. It is not possible at present to determinewhether the methane is biological or geologicalin origin. On Earth that distinction is made bymeasuring the carbon isotopic composition o

the methane. Biological processes strongly se-lect the lighter isotope, 12C, whereas geologicalprocesses do not. It is not yet possible to meas-ure the isotopic composition on Mars but thereare plans to do so on a orthcoming mission.

Exploration to date

There have been more than 40 attempted mis-sions to Mars, the rst in 1960. In the earlyyears there were many ailures but the success

rate now is very high. Only two successul mis-sions have had the specic goal o searching orlie, NASAs Viking 1 & 2 in 1976. Both werestationary landers with onboard laboratoriesto analyse or organic compounds and to testor gases produced by living organisms. Oneexperiment gave ambiguous results but it isnow accepted that no lie was detected. Inretrospect that result is not surprising. It is nowknown that the surace o Mars is highly oxi-

dising, so any organic compounds that mighthave been present would have been destroyed.In addition, Mars lacks both a substantial


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magnetosphere and an ozone shield, so bothcosmic and ultraviolet radiation reach the sur-ace and would kill any organisms present.

So is there lie on Mars?

We have learned over the last 50 years thatthe conditions essential or lie as we know itexisted widely on Mars early in its history, andstill exist in subterranean environments andoccasionally on the surace. But so ar the onlyhint that there is lie is the presence o methanein the atmosphere.

Within 20 years we will have much more in-ormation rom robotic vehicles and we may beable to gather enough inormation to suggestthe presence o lie. A nal demonstration mayrequire the return o samples, and such a mis-sion is being planned or 2020. That mission

will be both enormously complex and enor-mously expensive.

Figure 8: An electron micrograph o a broken surace on meteorite ALH84001. Thenumerous spheroidal structures are 20-50 nanometres wide. These and the worm-likestructure were at rst interpreted as ossil microbes.Image courtesy o NASA/nasaimages.org

I think it is very likely that there was microbiallie on Mars and probably still is. But I thinkwe will have to wait until astronauts go to Marslater this century to nally determine whetheror not there is or was lie there.

And the obvious question is, why bother? Theanswer is that the question o whether we arealone in the universe is one o the most pro-ound questions we ace. I there are microbeson Mars, and i we can demonstrate that theyhad a separate origin rom lie on Earth, thenwe will be able to predict that lie is abundantthroughout the universe. Somewhere out therewill be other industrial societies, probably armore advanced than ours.


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Paleolithic

nutrition:whatdid our ancestors

eat?Janette Brand MillerNeil Mann

Loren Cordain


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Paleolithic nutrition is the study odiets consumed by our early stone

age ancestors, members o our spe-cies who lived rom around 750,000

years ago up until 10,000 years ago (Figure 1).During this period, hominids relied on stonetechnology to sustain their scavenging, huntingand gathering liestyle (Figure 2). Paleolithicdiets are a subject o interest or various reasons.Apart rom the intrinsic value o knowing moreabout our past, many health experts have sug-gested that the native diet during human evolu-

tion is the healthiest diet, the one that meetsall our nutritional needs and to which we aregenetically adapted. Just as veterinarians try togive zoo animals a diet closest to that which theyconsumed in the wild, many nutritionists believethat the diet eaten or the greater part o one mil-lion years o human evolution is the ideal diet.Conversely, they believe that modern illnessessuch as type 2 diabetes and coronary heart dis-ease are a consequence o eating a diet to whichwe are not genetically adapted (Figure 3). Thelast 10,000 years ago (a mere tick on the evolu-tionary clock) have brought near inconceivablechanges to diet and physical activity.


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First stone tools appear in the fossil

record ~2.4 MYA

Why were theymade? What werethey used for?

Butchering ofscavenged animals

Flakes for slicingCore for chopping

Paleolithic Nutrition

Prof. Jennie Brand-Miller Human Nutrition Unit

Native Diet of Our Closest

Living Relative

94% plant foodschiefly ripe fruit6% animal foods - small

vertebrates & insects

A large metabolicallyactive gut is needed toprocess large amountsof less energeticallydense, fibrous plantfoods

Transition from Ape to Human

BipedalismOpposable thumbReduction in body

hair

Increase in brain size& complexity

Decrease in gut size& metabolic activity

Discordance Hypothesis

The discordancebetween modern diets

and paleolithic diets

contributes to manydiet related health

problems of modern

man

African Climate20 MYA and 7 MYA

Declining rainfall. Contraction of rainforest

Figure 1

Figure 3

Figure 5

Figure 2

Figure 4

Figure 6


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Paleolithic nutrition: what did our ancestors eat? |31

Climate dictates ood sources

For most o geological time, the worlds climatewas warmer and more homogeneous than itis today (Figure 4). Our pre-human ancestorswho lived in Arica >7 million years ago en-joyed a warm, moist environment and gathered

ripe ruits, leaves and berries rom the tropicalorests (Figure 4 and 5). But gradually the plan-et cooled. About 2.5 million years ago, a severeIce Age sent global temperatures plummetingand prompted the conversion o moist Aricanwoodland into much drier open savanna. Asthe grasslands expanded, the tree cover shrankand one or more species o orest dwellingchimpanzee evolved into bipedal hominids(Figure 6). Homo habilis who lived 2 million

years BP supplemented a largely vegetarian dietwith meat let over rom predators kills (i.e.they scavenged). But Homo erectus who lived1.5 million years BP is known to have activelyhunted. Many scientists believe that huntingwas the pressure that selected or the larger andlarger brain o our species, Homo sapiens sapiens(the phrase man the hunter originated withthis idea)(Figure 7 and 8).

As one Ice Age ollowed another, hunting and

shing became a dominant way o lie in bothwarm and cold environments. During Ice Ages,large amounts o water become locked intothe polar ice caps, making the whole planetdrier because less water alls as rain and snow.Plant growth slows, rainorests shrink andgrasslands dominate the landscape. Herbivorescame into their own and grazing animalsmultiplied in their millions. From 50,000years ago, we know that Neanderthals werecold-climate hunters o large game. Indeed,over winter they subsisted primarily on game.One large mammoth kill would have nourisheda amily group o 50 individuals or at least3 months. Similarly, Cro-Magnon man whoreplaced the Neanderthals about 35,000 yearsago, lived through the coldest o the Ice Ageson a high meat diet. The Hall o Bulls in theamous Lascaux Caves in southern France is atestament to the importance o animals to thepeople who lived 17,000 years ago (Figure 9).

Similarly, we know that the ancestors o theAborigines who inhabited Australia 40-50,000years ago led a hunting and shellsh gathering

existence. Even during the warm inter-glacials,parts o the world remained cold (e.g. Arcticand sub-arctic regions) and continued to havelittle vegetation. The human inhabitants othose regions maintained a hunting/shingexistence right up to recent times. Indeed, theInuit and other native Canadians are a modernday example o a group whose historic diet washigh in animal ood and low in plant matter.

During the early and mid 20th century, anthro-pologists studied the planets ew remaininghunter-gatherer societies. To their surprise,they ound them generally ree o the signsand symptoms o the so-called diseases ocivilization. Although their nutritional patternsprobably would not have been identical to

hominids living during the Paleolithic period,they represent the best window we have intothe range and quantity o wild and unculti-vated oods making up humanitys native diet.Consequently, the characterization and descrip-tion o hunter-gatherer diets has importantimplications in designing therapeutic diets thatreduce the risk or chronic diseases in modern,western cultures.

These ethnographic and anthropological stud-

ies tell us that there was no single, uniormdiet which typied the nutritional patternso all pre-agricultural humans. Humans weremasters o fexibility, with the ability to live in arain orest or near the polar ice caps. Yet, basedupon limited inormation, many anthropolo-gists incorrectly concluded that the universalpattern o subsistence was one in which plantoods contributed the majority o ood energy.However, more recent and comprehensiveethnographic compilations (Cordain et al,2000a) as well as quantitative dietary analysesin oraging populations, have been unable toconrm the conclusions o these earlier studies.In act, the later studies demonstrated that ani-mal oods, rather than plant oods, comprisedthe majority o energy in the typical hunter-gatherer diet.

Unortunately, in the context o western diets,increasing meat consumption (particularlyred and processed meat) is linked to a greaterrisk o cardiovascular disease. In countries likethe USA, meats contribute much o the at,


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Inclusion of more animal food in the

diet allowed brain to enlarge

How? Humans expend 20-25% of

RMR to fuel the brain wherea

chimps require 8% Two possibilities:

(1) increases in total metabolic

rate

(2) reduction in size &

metabolic rate of another

organ Aiello LC Wheeler. The expensive tissue hypothesisCurr Anthropol 1995 36:199-221

Evidence of Complex Big Game

Hunting in Homo Sapiens

Anatomically modernH. sapiens appear(~100,000 yrs ago)

A spear point wasfound lodged in the

vertebra of a giant

buffalo at Klasies RiverCave, South Africa

(60-120,000 yrs ago)

Dependence on gathered plant foodsFrequency Distribution of Subsistence Dependence (n = 229)

11

35

4245

35

30

23

6

20

0

5

10

15

20

25

30

35

40

45

50

Frequency

% Dependence

0 5 6 15 1625 2635 3645 46 55 5665 6675 7685 86 100

On average, plant

foods contributed

25-35% of energy

Only 13% obtained

more than half their

energy from plant

foods

Dependence on hunted animal foodsFrequency Distribution of Subsistence Dependence (n = 229)

47

21

11

5

9

Frequency

% Dependence

0 5 615 1625 2635 3645 4655 5665 6675 7685 86 100

Mode = (26-35%)

Median = (26-35%)

On average,

hunted animal

foods contributed26-35% of energy

Hall of Bulls -Lascaux Cave,France (17,000 yrs ago) Plant Foods

How important(quantitatively) weregathered foods in the diets

of pre-agricultural humans?

Only quantitative evidencecomes from observations of

early ethnographers who

studied worlds remnant

hunter-gatherers

Figure 7

Figure 9

Figure 11

Figure 8

Figure 10

Figure 12


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and more importantly, about one third o thesaturated at, the kind mostly clearly linkedto adverse outcomes. Thus, a high meat diet,regardless o its at quantity and type, is gener-ally perceived to be unhealthy and to promotecardiovascular and other chronic diseases.Yet Australian red meat derived rom grazinganimals is generally lean, low in saturated atand contains signicant amounts o healthylong chain omega-3 ats. Ourresearch providesevidence that the animal oods that dominatedhunter-gatherer diets were also low in saturatedat and high in good ats. This nutritional pat-tern would not have promoted atherosclerosis(hardening o the arteries) or chronic disease.

Conusion over pre-agricultural diets

Early theories on the natural, or native hu-man diet assumed that Paleolithic people wereskilled hunters o big game whose diets wereprimarily carnivorous in nature. However, byearly 1970s, this Man the Hunter explana-tion was being contested by Richard Lee andother anthropologists on the basis o evidencesuggesting that contemporary hunter-gathererpeoples consumed more gathered plants thanhunted animal ood (Lee, 1968) (Figure 10).For example, Lees studies o the Arican !Kungpeople demonstrated that gathered plant oodscomprised 67% o their average daily energyintake while hunted animal oods encompassedthe remaining third. Lee urther compiled datarom 58 hunter-gatherer societies who werelisted in the Ethnographic Atlas (Murdock,1967), showing that hunted animal ood madeup only 35 per cent o ood intake, irrespective

o latitude.

Over the next 30 or so years, Richard Leesanalysis was widely misinterpreted to meanthat gathered plant oods typically providedthe major ood energy in worldwide hunter-gatherer diets, while hunted animal oods madeup the balance. But this general perceptionis incorrect becausefshed animal oods mustbe summed with hunted animal oods in theanalysis o the ethnographic data to more cor-

rectly evaluate dietary plant to animal energyratios (i.e. the percentage o energy contributed

by plants versus animal oods). Our analysis(Figures 11-14) o Grays Ethnographic Atlasdata (Gray, 1999) showed that the dominantoods in most hunter-gatherer diets were de-rived rom animal ood sources. We ound thatnearly 3 in 4 o the worlds hunter gathererpopulations obtained at least hal o their oodenergy rom hunted and shed animal oods,whereas ewer than 1 in 7 obtained more thanhal their calories rom gathered plant oods.Not a single hunter-gatherer society was com-pletely vegetarian. The statistical mean amongall 229 hunter-gatherer societies in Grays atlasindicated that 68% o calories came rom ani-mal oods and 32% rom gathered plant oods(Figure 15).

Quantitative studies ohunter gatherer diets

The major limitation o ethnographic data isthat much o the inormation is subjective innature. Murdocks scoring or the ve basicsubsistence economies in the Ethnographic Atlaswere approximations, rather than preciselymeasured ood intake data. Fortunately, moreexact, quantitative dietary studies were car-ried out on a small number o hunter-gatherersocieties. Table 1 lists these studies and showsthe plant to animal subsistence ratios. Themean score or animal ood subsistence is 65%,while that or plant ood subsistence is 35%.These values are similar to our analysis o theentire (n = 229) sample o hunter-gatherersocieties (Figure 15). I we exclude the twopolar hunter-gatherer populations (who haveno choice but to eat animal ood because othe inaccessibility o plant oods) rom Table 1,

the mean score or animal subsistence is ~60%and that or plant ood subsistence is ~40%.Consequently, there is remarkably close agree-ment between the quantitative data in Table 1and the ethnographic data.

Other evidence or meat eating

Isotope studies o ossil bones can tell us moreinormation about the type o oods that ourancestors ate. Isotopic analysis o the skeletonso Neanderthals (Richards et al, 2000a) andPaleolithic humans (Richards et al, 2000b)


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Dependence on fished animal foodsFrequency Distribution of Subsistence Dependence (n = 229)

1

5 5

5

4

Freque

ncy

% Dependence

0 5 6 15 1625 2635 3645 4655 5665 6675 7685 86100

Mode = (46-55%)

Median = (26-35%)

On average, fishing

contributed 26-35%

of energy

Total dependence on animal foods

(hunted + fished)

0 02

6

23

30

35

45

42

46

0

5

10

15

20

25

30

35

40

45

50

Frequ

ency

% Dependence

0 5 615 1625 2635 3645 4655 5665 6675 7685 86 100

Mode = (66-75%)

Median = (86-100%)

On average, all

animal foods

(hunted and fished)contributed >66%

of energy

Dietary MacronutrientsHunter Gatherer vs Modern Values

CHO

22-40 %

Protein19-35 % Fat28-47 %

Hunter Gatherer Societies

n=133 (58.1%)

Fat34%

Protein

15%

CHO

49%

Present USA Values

NHANES III

ETOH-

3%

Recommended Dietary

Macronutrient Intake

CHO

55% or more

Fat30% or less

Protein

15%

American Heart Association

Recommended Diet

Plant:Animal RatiosHunter Gatherer Modern Diets

62 %

Plant

Food

38 %

Animal

Food

National Food ConsumptionSurvey 1987-88

Mean values,229 Hunter Gatherer

Societies

68 %

Animal

Food

32 %

Plant

Food

Foods not present in pre-agricultural diets

Breads, Cereals, Rice and Pasta Dairy Products Added Salt

Refined Vegetable Oils Refined Sugars

(except honey)Alcohol

Figure 13

Figure 15

Figure 17

Figure 14

Figure 16

Figure 18


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suggests that the dominance o animal oodsin the human diet was not simply a recentphenomenon limited to contemporary hunter-gatherers, but rather one with a long history.These studies provide objective evidence thatthe diets o hominids living in Europe during

the Paleolithic were indistinguishable rom thato carnivores such as arctic oxes and wolves.Indeed, hominids may have experienced genet-ic adaptations to animal-based diets early on intheir evolution, analogous to those o obligatecarnivores such as cats (elines).

Carnivorous diets reduce the evolutionaryselective pressures that act to maintain ana-tomical and physiological eatures needed toprocess and metabolize large amounts o plant

matter. Like cats, humans have experienceda reduction in gut size and metabolic activity,along with a concurrent expansion o brainsize (Figure 7). This occurred at the very sametime that more and more energetically denseanimal ood was incorporated. The brain is avery energy-demanding organ, responsible orabout one quarter o our basal metabolic rate.Further, similar to obligate carnivores, humanshave a limited ability to manuacture the longchain, highly polyunsaturated atty acids thatcharacterize our complex brain and nervoussystem. Long chain polyunsaturated atty acids

are essential cellular lipids that are ound onlyin animal oods. The implication is that by eat-ing abundant pre-ormed sources o these attyacids, our bodies gradually lost the ability tosynthesise them in house.

Finally, our species (again like cats) has a

limited capacity to synthesize the aminoacid taurine rom its precursor amino acids.Vegetarian diets are known to result in lowerblood concentrations o taurine. This impliesthat the need to synthesize taurine may havebeen unnecessary because dietary sources opre-ormed taurine had relaxed the selectivepressure to maintain the metabolic machinery.

There are additional signs that we were grow-ing dependent on animal ood sources. One o

our essential micronutrients is Vitamin B12 andound only in animal oods. Similarly, the rich-est sources o iron, iodine, olic acid and vita-min A are animal oods. The most common nu-trient deciencies today are associated with lowmeat consumption. Iron deciency anaemiais prevalent in both rich and poor countries,while iodine deciency aects up to 2 billionpeople world wide, resulting in goitre, cretin-ism and enough mental retardation to reduce

a populations average IQ. (Incidentally, iodinedeciency is rising sharply in Australia becausedairy manuacturers no longer use iodophors as

Table 1: Quantitatively determined proportions o plant and animal ood in hunter-gatherer diets.

Population Location Latitude % animal ood % plant ood

Aborigines Australia 12S 77 23

Ache Paraguay 25S 78 22

Anbarra Australia 12S 75 25Ee Arica 2N 44 56

Eskimo Greenland 69N 96 4

Gwi Arica 23S 26 74

Hadza Arica 3S 48 52

Hiwi Venezuela 6N 75 25

!Kung Arica 20S 33 67

!Kung Arica 20S 68 32

Nukak Columbia 2N 41 59

Nunamiut Alaska 68N 99 1Onge Andaman 12N 79 21


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cleansing agents in dairy actories). Folic aciddeciency causes a birth deect in which thebrain and spinal cord do not develop normally,a condition known as neural tube deect.Although dark green leay vegetables are a goodsource o olic acid, the very richest source isanimal liver, a commodity regularly consumedby our hunter-gatherer ancestors. Finally, hu-mans have a nite capacity to convert the yel-low/orange coloured carotenoids in plant oods

into vitamin A. Today, vitamin A deciencyblindness is the most common cause o visionloss in the world and again, the richest sourceso vitamin A are liver and animal fesh. Sogradually, but surely, we evolved a metabolismthat depended on at least moderate intake oanimal oods.

Hunter-gathereroraging strategies

Our analyses o both the ethnographic data andthe quantitative dietary data (Table 1) showthat animal oods were our preerred energysource, even when plant ood sources wereavailable year round such as in the tropics.Only when it was dicult to procure animalood sources, or when energy-dense, easilyprocured plant oods were available (eg themongongo nut or the South Arican !Kungpeople), did plant oods prevail as a major en-

ergy component in hunter-gatherer diets.

Foraging humans are similar to other animalsin natural settings in that they attempt tomaximize the energy capture rate, i.e. theratio between the energy obtained rom a oodsource compared to the energy expenditureneeded to acquire it while hunting, shingor gathering (this is known as the OptimalForaging Theory). Table 2 shows the energyreturn rates or a variety o plant and animaloods that were known components o hunter-

gatherer diets. Clearly, animal oods yield thehighest energy return rates, and larger animalsgenerally produce greater energy returns thansmaller animals. Although the potential oodmass would be similar between a single deerweighing 45 kg and 1,600 mice weighing 30 geach, oraging humans would have to expendsignicantly more energy capturing the 1,600mice than a single deer. Hence, the killing olarger animals increases the energy capture/

energy expenditure ratio not only because itreduces energy expenditure, but because it in-creases the total energy captured.

Due to the relative constancy o the proteincontent o an animals muscle mass, the energydensity o an edible carcass is almost entirelydependent upon its body at content. Varyingamounts o body at determine the protein toat energy ratio in an edible carcass. Becausesmaller animal species have proportionately

less body at than larger species, their carcassescontain more protein as a percentage o theiravailable ood energy. Hunter-gatherers tended

The USDA Food Pyramid

Fats Oils & Sweets

use sparingly

Milk, Yogurt & Cheese

2-3 Servings

Vegetables

3-5 Servings

Bread, Cereal, Rice

& Pasta

6-11 Servings

Fruit

2-4 Servings

Meat, Poultry, Fish, Dry Bean

Eggs & Nuts

2-3 Servings

Human Evolutionary Food Pyramid

Figure 19 Figure 20


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to shun very small animals or at-depleted ani-mals because o their excessive protein content.Historical accounts documented the adversehealth eects that occurred when people wereorced to rely solely on at-depleted, wild ani-

mals (Speth & Spielmann, 1983). Excessiveprotein consumption without additional sourc-es o at or carbohydrate caused a condition de-scribed as rabbit starvation in early Americanexplorers. They suered nausea, diarrhea andeven death i very lean small animals were theonly source o ood. Clinically, this syndromeis probably caused by the nite ability o theliver to up-regulate the rate-limiting enzymesthat synthesise urea, culminating in very high

levels o ammonium ions and acidic aminoacids in the blood. For the oraging human, theavoidance o excessive dietary protein was an

important actor in shaping their ood procure-ment strategies. Lean meat, thereore, couldnot be eaten in unlimited quantities, but ratherhad to be accompanied by sucient at, or bycarbohydrate derived rom plant ood sources.

This simple physiological act could explainour innate drive to consume atty and sweetoods.

Modern vs traditionalood choices

Beore the development o agriculture andanimal husbandry, dietary choices would havebeen limited to minimally processed, wild plant

and animal oods. With the initial domestica-tion o plants and animals, the original nutrientcharacteristics o oods changed, subtly at rst

Table 2: Energy return rates upon encounter rom oraged oods.

Food Food Type Return rate (kcal/hr)

Collared peccary Animal 65,000

Antelope, deer, bighornsheep

Animal 16,000 32,000

Jack rabbits Animal 13,500 15,400Cottontail rabbits, gophers Animal 9,000 10,800

Paca Animal 7,000

Coati Animal 7,000

Squirrel (large) Animal 5,400 6,300

Roots Plant 1,200 6,300

Fruits Plant 900 6,000

Armadillo Animal 5,900

Snake Animal 5,900

Bird Animal 4,800Seeds Plant 500 4,300

Lizard (large) Animal 4,200

Squirrel (small) Animal 2,800 3,600

Honey Plant 3,300

Ducks Animal 2,000 2,700

Insect larvae Animal 1,500 2,400

Fish Animal 2,100

Palm heart Plant 1,500

Acorns Plant 1,500

Pine nuts Plant 800 1,400+Mongongo nuts Plant 1,300

Grass seeds Plant 100 1,300


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but more rapidly with advancing technologyater the Industrial Revolution. Food processingprocedures were developed which had pro-ound physiological implications.

Today we eat many types o ood that wereabsent rom the diet o Paleolithic people.

Dairy products, cereals, rened sugars, renedvegetable oils, and alcohol make up over 70%o the total daily energy consumed by people indeveloped nations (Figure 16). But these typeso oods would have contributed little or noneo the energy in the typical pre-agricultural hu-man diet. Additionally, mixtures o oods thatmake up much o our present diet(eg, cookies,cake, breakast cereals, bagels,rolls, muns,crackers, chips, snack oods, pizza, sot drinks,

candy, ice cream, condiments, and salad dress-ings) were absent.

Dairy foods Humans, like all mammals, wouldhave consumed the milk o their own speciesduring inancy. However, aterweaning, theconsumption o milk and milk products oothermammals would have been minimal.Sheep, goats and cows were not domesticateduntil ~10,000 years ago and direct evidence odairying datesto only ~6000 years ago. Most o

the worlds population still does not consumemilk beyond inancy. It should not be surpris-ing thereore to learn that more than 80% ohumans do not have the capacity to hydrolyselactose, the carbohydrate in milk, ater earlychildhood. However, European Caucasians andtheir descendents in America and Australia,who have been exposed to dairying or severalthousand years, can generally digest lactosewell throughout lie.

Cereals Wild cereal grains are usually small,dicult to harvest,and virtuallyindigestiblewithout processing (grinding) and cooking. Forthis reason,Paleolithic people ate little o them.Grinding tools in the ossil recordrepresents areliable indication o when and where cultures

began to include cereal grains in their diet.

Ground stone mortars, bowls, and cup holesrst appearedrom 40,000 years ago to 12,000years ago. Domestication o emmerand einkornwheat heraldedthe beginnings o early agricul-ture in southeastern Turkey about 10,000 yearsago. There was thereore little or no previous

evolutionary experienceor cereal grain con-sumption throughout human evolution. Again,it should not be surprising to learn that manypeople are allergic to the gluten protein oundin wheat, rye and barley. Known as celiacdisease, it causes the bodys immune system toattack itsel and aects more than one in every133 people.

Today, most cereals consumed inthe west-ern diet are highly processed rened grains.Precedingthe Industrial Revolution, all cerealswere ground with theuse o stone milling tools,and unless the four was sieved,it containedthe entire contents o the cereal grain, includ-ingthe germ, bran, and endosperm. Withthe invention o mechanizedsteel roller mills

and automated siting devices in the latter

part o the 19th century, the nutritional andphysiological characteristicso milled grainchanged, becoming virtually pure starch romjust the seed endosperm. As a consequence,the oods made rom ne fours, such as bread,are quickly digested and absorbed, and raiseblood sugars rapidly when consumed. Manyrecent studies suggest that carbohydrates thatare digested and absorbed quickly (known ashigh glycemic index oods), increase the risk

o chronic diseases such as type 2 diabetes andcardiovascular disease (Barclay et al. 2008).

Alcohol In contrast to dairy products, cerealgrains, rened sugars,and rened oils, alcoholconsumption representsa relatively minor rac-tion (1 or 2%) o the total energy consumed inwestern diets. The earliest evidence or winedrinking rom domesticated vinescomes rom apottery jar dated ~7000 years BP rom northernIran. The ermentation process that produceswine takes place naturallyand, without doubt,must have occurred countless times beorehu-mans learned to control the process. As grapesreach theirpeak o ripeness in the all, theymay swell in size and burst,thereby allowingthe sugars in the juice to be exposed to yeasts

growing on the skins and to produce carbondioxide and ethanol.Because o seasonal fuc-tuations in ruit availabilityand the limitedliquid storage capacity o hunter-gatherers,it is

likely that ermented ruit drinks, such as wine,wouldhave made an insignicant contributionto totalenergy in Paleolithic diets.


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Salt The total quantity o salt included in thetypical diet o westernized nations amounts

to nearly 10 g/day. About 75% is derived romsalt added to processedoods by manuactur-ers; 15% comes rom discretionary sources(ie,cooking and table salt use), and the remainderoccursnaturally in basic oodstus. The system-atic mining, manuacture, and transportationo salthave their origin in the last 10,000 years.The earliest saltuse is thought to have takenplace in China about 6000 BC. Paleolithichunter-gatherers living in coastal areasprobablydipped ood in seawater or used dried saltin amanner similar to nearly all Polynesian socie-ties at thetime o European contact. But mostrecentlystudied inland hunter-gatherers add noor little salt to theirood.

Diet and chronic diseasein hunter-gatherers

Dietary at

In our analysis o hunter-gatherer diets(Cordain et al, 2000), we ound that mostgroups exceeded the dietary recommendationto eat 30% or less o energy as at (Figures 17and 18). In act, over hal o them consumed

amounts not too dissimilar to current westernand Mediterranean dietary intakes. Despitethis, the available evidence suggests that hunt-er-gatherers were generally ree o the signs andsymptoms o cardiovascular disease. Researchshows that indigenous populations that derivethe majority o their diet rom animal productshave surprisingly low levels o cholesterol andother ats in the blood. Moreover, death certi-cates, autopsies and clinical studies indicate alow incidence o coronary heart disease amongthe Inuit and other polar populations, consum-ing high intakes o animal oods. However, inwestern diets, higher animal ood consumptionis requently associated with increased mortal-ity rom chronic disease. The low incidenceo cardiovascular disease among indigenouspopulations subsisting largely on animal oodsrepresents a paradox.

There is now strong evidence that the absoluteamount o dietary at is less important in re-ducing the risk or cardiovascular disease thanthe type o at. Fatty acids that increase blood

cholesterol levels include lauric acid (C12:0),myristic acid (C14:0), palmitic acid (C16:0),and some trans atty acids (Grundy, 1997),whereas monounsaturated (MUFA) and poly-unsaturated (PUFA) atty acids reduce choles-terol levels. Stearic acid (C18:0), the major attyacid in chocolate and lean red meat is neutral.Omega-3 long chain PUFA, ound in sh andseaood in general and Australian grass ed beeand lamb, have wide ranging protective capaci-ties including the ability to reduce blood lipids.Consequently, it is possible to consume highat diets that do not produce an adverse bloodlipid prole or cardiovascular disease.

In their classic study o Greenland Eskimoswho had a near absence o cardiovascular dis-

ease, Bang and Dyerberg (1980) contrasted thedietary and blood lipid proles o the Eskimosto Danes (Table 3). Despite a much greater ani-mal ood intake than the Danes, the Eskimosmaintained a more healthul blood lipid prole.The reduced cholesterol levels in the Eskimosare likely accounted or by the higher dietaryintake o good ats. The protein intake o theEskimos was more than twice as high as theDanes, and this pattern (elevated protein at theexpense o carbohydrate) is characteristic o

hunter-gatherers (Cordain et al, 2000a).

Dietary protein

Our analyses o contemporary hunter-gathererdiets show that the average protein intake wasas high as 35% energy (Figure 16). This ismore than twice the level consumed by cur-rent western populations (~15% energy). Highprotein intake in western diets is perceivedto be linked to high calcium excretion in the

urine and aster progression o kidney disease.Yet, paradoxically, high protein diets havebeen shown to improve metabolic control intype 2 diabetes patients. In her classic study oAustralian Aborigines temporarily reverting toa hunter-gatherer liestyle, Kerin ODea showedthat animal oods contributed ~65% o the totalenergy, producing an overall macro-nutrientdistribution o 54% protein, 33% carbohydrateand 13% at energy. Following a 7-week periodliving as hunter-gatherers in their traditional

country in north-western Australia, 10 diabetic,overweight Aborigines experienced either a


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great improvement or complete normalizationo all o the major metabolic abnormalitiescharacteristic o diabetes (ODea, 1984).

The ossil record indicates pre-agricultural hu-mans generally maintained greater bone massthan modern humans and hence greater bonestrength and resistance to ractures (Bridges,

1995; Ruet al, 1993). Greater bone strengthhas been attributed to the greater activity pat-terns o pre-agricultural humans, which in turnwould have increased bone loading. It is alsoquite likely that the high ruit and vegetableconsumption in hunter-gatherer diets wouldhave buered the high acid load and subse-quent high calcium excretion brought aboutby a high protein diet. In western diets, meats,cheeses and cereal grains yield high potential

renal acid loads and hence may promote oste-oporosis (thinning o the bones) by producinga net metabolic acidosis. In contrast, ruits andvegetables yield a net alkaline renal load, andhigh ruit and vegetable diets have been shownto decrease urinary calcium excretion rates.Consequently, in hunter gatherer populationsconsuming high protein diets, a concomitantconsumption o high levels o ruits and vegeta-bles may have countered the eects o a highprotein diet.

Dietary carbohydrate

Our studies also demonstrate that the carbo-hydrate content o hunter-gatherer diets wouldhave ranged rom 22 to 40% o total energy(Figure 16). The values within this range areconsiderably lower than average values in west-ern diets or recommended levels (50-60% or

more o total energy). Although current adviceto reduce risk o cardiovascular disease is toreplace saturated ats with carbohydrate (Figure17), there is mounting evidence to indicatethat low at, high carbohydrate diets may elicitundesirable changes in blood ats, includingreductions in the good cholesterol (HDL) andtriglycerides. Because o these untoward bloodlipid changes, substitution o MUFA or satu-rated ats has been suggested as a more eec-tive strategy than substitution o carbohydrateor saturated ats in order to lower the risk ocardiovascular disease.

Hunter gatherer diets would not only havecontained less carbohydrate than that typicallyound in western diets, but there are impor-tant qualitative dierences in the types ocarbohydrates. Western diets are characterizedby carbohydrate oods with a high glycemicindex (e.g. potatoes, bread, processed cerealproducts) whereas the wild plant oods whichwould have been consumed by hunter-gather-ers generally maintain a high ber content, are

Table 3: Dietary and blood lipid characteristics o Greenland Eskimos and Danes.

Variable Eskimos Danes

Dietary intake:

Protein (% energy) 26.0 11.0

Fat (% energy) 37.0 42.0Carbohydrate (% energy) 37.0 47.0

Saturated at (% total at) 22.8 52.7

Monounsaturated at (% total at) 57.3 34.6

Polyunsaturated at (% total at) 19.2 12.7

n-6 PUFA (g) 5.4 10.0

n-3 PUFA (g) 13.7 2.8

Blood lipid values

Total cholesterol (mmol/liter) 5.33 + 0.78 6.24 + 1.00

Triglycerides (mmol/liter) 0.61 + 0.44 1.32 + 0.53


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slowly digested and produce low glycemic andinsulin responses. Observational studies sug-gest that oods with a high glycemic load andlow ber content increase the risk or type 2diabetes (Barclay et al, 2008).

Other environmental actors

It is likely that hunter-gatherers consumed veryhigh intakes o antioxidants and phytonutrientsand undertook more intense physical exerciseor work patterns (Cordain et al, 1998). Thesecharacteristics would have provided pre-agri-cultural people with urther protection romchronic diseases such as diabetes. Biochemicalstudies o hunter-gatherers have shown highplasma concentrations o olate and vitaminB12. Adequate intake o these two vitamins

along with vitamin B6 reduce homocysteine, animportant risk actor or cardiovascular disease.Hunter-gatherers rarely i ever added salt totheir oods, and studies o salt-ree YanomamoIndians have shown these indigenous peopleto maintain low blood pressures that do notincrease with age. Finally, except or certainAmerican Indian societies (starting about 5,000years ago), regular smoking o tobacco was un-known in hunter-gatherers. Any or all o thesedietary and environmental elements wouldhave operated together with the macronutrientcharacteristics o hunter-gather diets to reducesigns and symptoms o the chronic diseasesthat plague western societies.

Conclusions

The diet o our ancestors was characterizedby higher intake o meat and lower intakeo plant oods than is generally recognized.

Modern human beings display physiologicaleatures which suggest an increasingly carnivo-rous diet during human evolution. Our largebrains increased in size at the expense o thegastronintestinal tract and dictated high intakeo nutrient-rich oods. The high reliance onanimal oods may not have elicited an adverseblood lipid prole because o the benets ohigh dietary protein and low level o dietarycarbohydrate. Although at intake would havebeen similar to or higher than that ound in

western diets, there were important qualitativedierences. The high levels o MUFA and PUFA

and omega-3 atty acids, would have servedto inhibit the development o cardiovasculardisease. Other dietary characteristics includinghigh intakes o antioxidants, bre, vitamins andphytochemicals along with a low salt intakemay have operated synergistically with liestylecharacteristics (more exercise, less stress andno smoking) to urther deter the developmento disease. The modern healthy ood pyramidwith its oundation based on cereals rich in car-bohydrate supplemented with small amountso animal oods (Figure 19) diers greatly romthe human evolutionary pyramid (Figure 20).Yet it is still possible to consume a healthydiet based on evolutionary principles in whichthe quality o at, protein and carbohydrateare more critical that their quantity or energy

distribution. Indeed, the insights gained romPaleolithic nutrition are likely to infuence u-ture dietary guidelines around the world.

Although concerted attempts were made to acknowledge the

source o all images, in some cases this could not be ascertained

Please contact the author i an inringement has taken place

Further reading

Barclay A, Petocz P, McMillan-Price J, Flood

VM, Prvan T, Mitchell P, Brand-Miller JC.

Glycemic index, glycemic load and chronicdisease risk a meta-analysis o observationalstudies. Am J Clin Nutr 2008; 87: 627-37.

Cordain L, Watkins BA & Mann NJ (2001):Fatty acid composition and energy density ooods available to Arican hominids: evolution-ary implications or human brain development.World Rev Nutr Diet. 90, 000-000.

Cordain L, Brand Miller J, Eaton SB, Mann N,

Holt SHA & Speth JD (2000a): Plant-animalsubsistence ratios and macronutrient energyestimations in worldwide hunter-gatherer diets.

Am J Clin Nutr. 71, 682-692.

Cordain L, Brand Miller J, Eaton SB & MannN (2000b): Macronutrient estimations inhunter-gatherer diets. Am. J. Clin. Nutr. 72,1589-1590.

Cordain L, Gotshall RW, Eaton SB & Eaton SB

(1998): Physical activity, energy expenditureand tness: an evolutionary perspective. Int. J.Sports Med. 19, 328-335.


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Dahlberg F (1981): Introduction. In: Womanthe Gatherer, ed. F Dahlberg, pp 1-33. NewHaven: Yale University Press.

Eaton SB & Konner M (1985): Paleolithicnutrition. A consideration o its nature and cur-rent implications. N. Engl. J. Med. 312, 283-

289.

Eaton SB, Konner M & Shostak M (1988a):Stone agers in the ast lane: chronic degenera-tive diseases in evolutionary perspective. Am. J.Med. 84,739-749.

Eaton SB, Shostak M & Konner M (1988b):The Paleolithic Prescription. New York: HarperRow.

Kaplan H & Hill K (1992): Human subsistence

behavior. In: Evolution, Ecology and HumanBehavior, eds, EA Smith & B Winterhalder, pp167-202. Chicago: Aldine.

Kaplan H, Hill K, Lancaster J & Hurtado AM(2000): A theory o human lie history evolu-tion: diet, intelligence, and longevity. Evol.Anthropol. 9, 156-185.

Lee RB (1968): What hunters do or a living, orhow to make out on scarce resources. In: Man

the Hunter, eds. RB Lee & I DeVore, pp 30-48.Chicago: Aldine.

Lee RB (1979): The !Kung San: Men, Women,and Work in a Foraging Society. Cambridge:Cambridge University Press.

Mann, N (2000). Dietary lean red meat and hu-man evolution. Eur J Nutr 39: 71-79.

McArthur M (1960): Food consumption anddietary levels o groups o aborigines living on

naturally occurring oods. In: Records o theAmerican-Australian Scientic Expedition toArnhem Land, ed. CP Mountord, pp 90-135.Melbourne: Melbourne University Press.

Meehan B (1982): Shell Bed to Shell Midden.Canberra: Australian Institute o AboriginalStudies.

Murdock GP (1967): Ethnographic atlas: asummary. Ethnology 6,109-236.

ODea K (1984): Marked improvement incarbohydrate and lipid metabolism in diabetic

Australian Aborigines ater temporary reversionto traditional liestyle. Diabetes 33, 596-603.

Richards MP & Hedges RM (2000b): Focus:Goughs Cave and Sun Hole Cave humanstable isotope values indicate a high animalprotein diet in the British Upper Palaeolithic.J

Archaeol Sci27, 1-3.

Sinclair HM (1953): The diet o CanadianIndians and Eskimos. Proc. Nutr. Soc. 12, 69-82.

Speth JD (1989): Early hominid hunting andscavenging: the role o meat as an energysource. J. Hum. Evol. 18, 329-343.

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