Giants of Geology

Robert Hooke

James Hutton

William Smith

Charles Lyell

Charles Darwin

A. R. Wallace

Nicola Steno

1600 1650 1700 1750 1800 1850 1900 1950

Chapter 3. Evolution

Charles Darwin & Natural Selection Evidence of evolution – the fossil record Mechanism of evolution – DNA A modification - Punctuated Equilibrium Creationism – a formidable opponent

Chapter 3. Evolution

Charles Darwin & Natural Selection

Evidence of evolution – the fossil record

Mechanism of evolution – DNA A modification - Punctuated

Equilibrium Creationism – a formidable

opponent

Darwin at age 68 in 1877 “the father of evolutionary biology “

The Voyage of H.M.S. Beagle

1831 December 27 Tuesday (about 11:00 AM)After a few delays, H.M.S. Beagle headed out from Plymouth with a crew of 73 under clear skies and a good wind. Darwin became sea-sick almost immediately.

Darwin at age 31 in 1840

theory of natural selection Darwin was not the first

person to consider that life on this planet evolved, but he was the first to come up with a viable working mechanism on how it happened.

1854 December

At last Darwin figured out how populations split off into separate species. Using the industrial revolution as a metaphor, he saw that populations of animals, like industry, expand and specialize to fit into niches with competition acting as the driving force. He saw nature as the ultimate "factory." However, Darwin preferred not to make much of this metaphor because it seemed to depend more on economic principles rather than pure science.

Darwin at age 45 in 1854 http://www.aboutdarwin.com/timeline/time_06.html#0080

A. E. Wallace – Darwin’s Equal?

1858 June 18Darwin received a paper from Alfred Russel Wallace, who was still at the Malay Archipelago. The paper was titled: "On the Tendency of Varieties to Depart Indefinitely from the Original Type." Darwin was shocked! Wallace had come up with a theory of natural selection that was very similar to his own. The paper contained concepts like "the struggle for existence," and "the transmutation of species."

Upon further examination Darwin saw that Wallace had some ideas about natural selection that he did not agree with. For one thing, Wallace tried to mix social morality with natural selection, proposing an upward evolution of human morals which would eventually lead to a socialist utopia (Darwin's natural selection had no goal). What's more, Wallace believed that cooperation in groups aided in the progress of mankind (Darwin saw natural selection as being influenced by competition). Finally, Wallace's natural selection was guided by a higher spiritual power (there was no divine intervention in Darwin's version).

Alfred Russel Wallace in 1848, age 25

"On the Origin of Species by means of Natural Selection."

1859 November 22"Origin of Species" went on sale to the public today at a price of 15 shillings. 1,250 copies were printed, most of which sold the first day. It was an immediate success and Darwin started the same day editing the work for a second edition.

First Edition of “Origin of Species”

Examples of Natural Selection

Darwin's Finches

Darwin's finches are an excellent example of the way in which species' gene pools have adapted in order for long term survival via their offspring. The Darwin's Finches diagram illustrates the way the finch has adapted to take advantage of feeding in different ecological niche's.

Their beaks have evolved over time to be best suited to their function. For example, the finches who eat grubs have a thin extended beak to poke into holes in the ground and extract the grubs. Finches who eat buds and fruit would be less successful at doing this, while their claw like beaks can grind down their food and thus give them a selective advantage in circumstances where buds are the only real food source for finches.

Examples of Natural Selection

Industrial Melanism

Polymorphism pertains to the existence of two distinctly different groups of a species that still belong to the same species. Alleles for these organisms over time are governed by the theory of natural selection, and over this time the genetic differences between groups in different environments soon become apparent, as in the case of industrial melanism.

Industrial melanism occurs in a species called the peppered moth, where the occurrence has become of more frequent occurrence since the beginning of the industrial age. The following argument elaborates the basis of principles involved in natural selection as far as industrial melanism is concerned.

Pollution, which is more common in today's world since the industrial age causes a change in environment, particularly in the 1800's when soot would collect on the sides of buildings from chimneys and industries and make them a darker color.

The resultant effect was that the peppered moth, which had a light appearance was more visible against the darker backgrounds of sooty buildings.

This meant that predators of the peppered moth could find them more easily as they are more visible against a dark background.

Due to mutations, a new strain of peppered moth came to existence, where their phenotype was darker than that of the white peppered moth.

This meant that these new, darker peppered moths were once again harder to track down by their prey in environments where industry has taken its toll.

In this instance, natural selection would favor the darker moths in polluted environments and the whiter moths in the lesser polluted environments due to their ability to merge in with their environmental colors and lessen the chances of them being prone to a predator.

http://www.biology-online.org/2/11_natural_selection.htmhttp://www.biology-online.org/2/11_natural_selection.htm

Examples of Natural Selection Sickle Cell Trait

Consider this argument of natural selection in the case of sickle cell trait, a genetic defect common in Africa.

Sickle cell trait is a situation that occurs in the presence of a recessive allele coding for haemoglobin, a substance in the blood responsible for the transport of gases like oxygen. The presence of the allele is either partially expressed recessively (sickle cell), or fully expressed by a complete recessive expression which results in full blown anaemia. If this particular allele is dominant, no sickle cell trait is expressed in the phenotype.

The above occurrences in the case of a recessive allele result in structural defects of red blood cells, severely reducing the organisms capacity to uptake oxygen. It was pointed out that in Africa, there is a high frequency of this mutation, where cases of malaria were high. A substantiated link was made noting those who suffer sickle cell trait or anaemia were immune to the effects of malaria.

This is yet again natural selection at work. Although sickle cell trait or anaemia are not advantageous characteristics on their own, they prove to be advantageous in areas where malaria proves to be a greater threat to preserving the genome (i.e. surviving). The incomplete dominance of this genetic expression proves favourable either way. This is how science has understood natural selection since the first studies involving Darwin. In

http://www.biology-online.org/2/11_natural_selection.htmhttp://www.biology-online.org/2/11_natural_selection.htm

WHAT IS EVOLUTION? Most non-scientists seem to

be quite confused about precise definitions of biological evolution.

When discussing evolution it is important to distinguish between the existence of evolution and various theories about the mechanism of evolution.

WHAT IS EVOLUTION?

One of the most respected evolutionary biologists has defined biological evolution as follows:

"In the broadest sense, evolution is merely change, and so is all-pervasive; galaxies, languages, and political systems all evolve.

Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual.

The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions." - Douglas J. Futuyma in Evolutionary Biology, Sinauer Associates 1986

http://www.talkorigins.org/faqs/evolution-definition.html

WHAT IS EVOLUTION? It is important to note that biological evolution refers to

populations and not to individuals and that the changes must be passed on to the next generation. In practice this means that,

Evolution is a process that results in heritable changes in a population spread over many generations.

This is a good working scientific definition of evolution; one that can be used to distinguish between evolution and similar changes that are not evolution.

Another common short definition of evolution can be found in many textbooks:

"In fact, evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next." – (Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989 Worth Publishers, p.974 )

Meaning of ALLELE

Definition: [n]  one of two alternate forms of a gene that can have the same locus on homologous chromosomes and are responsible for alternative traits; "some alleles are dominant over others"

Evolution (cont.)

When biologists say that they have observed evolution, they mean that they have detected a change in the frequency of genes in a population.

POOR DEFINITIONSThe Oxford Concise Science Dictionary:

"evolution: The gradual process by which the present diversity of plant and animal life arose from the earliest and most primitive organisms, which is believed to have been continuing for the past 3000 million years."

This is poor because not only does this definition exclude prokaryotes, protozoa, and fungi, but it specifically includes a term "gradual process" which should not be part of the definition.

More importantly the definition seems to refer more to the history of evolution than to evolution itself. Using this definition it is possible to debate whether evolution is still occurring.

Also, this definition provides no easy way of distinguishing evolution from other processes. For example, is the increase in height among Caucasians over the past several hundred years an example of evolution? Are the color changes in the peppered moth population examples of evolution?

DEFINITION (CONT.) “Recently I read a statement from a creationist who

claimed that scientists are being dishonest when they talk about evolution. This person believed that evolution was being misrepresented to the public. The real problem is that the public, and creationists, do not understand what evolution is all about. This person's definition of evolution was very different from the common scientific definition and as a consequence he was unable to understand what evolutionary biology really meant. This is the same person who claimed that one could not "believe" in evolution and still be religious! But once we realize that evolution is simply "a process that results in heritable changes in a population spread over many generations" it seems a little silly to pretend that this excludes religion! “

Laurence Moran , January 22, 1993

Laurence Moran , January 22, 1993, http://www.talkorigins.org/faqs/evolution-definition.html

BAD DEFINITIONSStandard dictionaries are even

worse:

"evolution: ...the doctrine according to which higher forms of life have gradually arisen out of lower.." - Chambers

"evolution: ...the development of a species, organism, or organ from its original or primitive state to its present or specialized state; phylogeny or ontogeny" - Webster's

These definitions are simply wrong. Unfortunately it is common for non-scientists to enter into a discussion about evolution with such a definition in mind. This often leads to fruitless debate since the experts are thinking about evolution from a different perspective. When someone claims that they don't believe in evolution they cannot be referring to an acceptable scientific definition of evolution because that would be denying something which is easy to demonstrate. It would be like saying that they don't believe in gravity!

Chapter 3. Evolution

Charles Darwin & Natural Selection Evidence of evolution – the fossil record Mechanism of evolution – DNA A modification - Punctuated Equilibrium Creationism – a formidable opponent

Fossils

Evolution is a fact, not a theory

Evidence comes from the fossil record, but also from biology, anthropology

What is the fossil evidence? Petrified remains of earlier life that records systematic changes

Fossil hominid skulls – missing links no longer missing?

Some of the figures have been modified for ease of comparison Smithsonian Institution.)

Fossil hominid skulls. (A) Pan troglodytes, chimpanzee, modern (B) Australopithecus africanus, STS 5, 2.6 My (C) Australopithecus africanus, STS 71, 2.5 My (D) Homo habilis, KNM-ER 1813, 1.9 My (E) Homo habilis, OH24, 1.8 My (F) Homo rudolfensis, KNM-ER 1470, 1.8 My (G) Homo erectus, Dmanisi cranium D2700, 1.75 My (H) Homo ergaster (early H. erectus), KNM-ER 3733, 1.75 My (I) Homo heidelbergensis, "Rhodesia man," 300,000 - 125,000 y (J) Homo sapiens neanderthalensis, La Ferrassie 1, 70,000 y (K) Homo sapiens neanderthalensis, La Chappelle-aux-Saints, 60,000 y (L) Homo sapiens neanderthalensis, Le Moustier, 45,000 y (M) Homo sapiens sapiens, Cro-Magnon I, 30,000 y (N) Homo sapiens sapiens, modern

EVIDENCE OF EVOLUTION

The best arguments for evolution include:

Branching organization of life Homology Vestigial structures and imperfections Embryonic history Biogeography

Fig. 3.5EVIDENCE FOR EVOLUTION 1.

Branching organization of life.

The branching pattern of life is indicated by changes (mutations) in the molecule cytochrome c. The molecule is very similar in humans and apes, but progressively different in other species. Distance between nodes is proportional to measured change.

EVIDENCE FOR EVOLUTION 2. Homology

Homology of forelimbs of various vertebrates, similar bones have similar colors. Although the functions are different the bones are structurally similar and develop from similar embryonic tissues. Simplest explanation is that all evolved from a common ancestor, the lobe-finned fish.

Homology: organs with different functions are built with same basic parts.

EVIDENCE FOR EVOLUTION 3. Vestigal structures and imperfections

A. Splint bones in horses, serve no useful function and are in fact detrimental, since breaking one can hobble a horse for life. Both a vestige and imperfection.

B. Pelvic and thigh bones in whales and snakes serve no purpose but show that both once had functional hind limbs.

C. Panda’s thumb. Their true thumb has fused into a digit, but because they need a functional thumb, a modified wrist bone serves as one. A classic example of an imperfection.

Next slide: Ernst Haeckel’s famous depiction of embryos at various stages of development. Early stages are remarkably similar regardless of adult form. Note presence of gill slits and similarity of vertebral column (backbone).

Why should such similarities exist if all did not have a common ancestor?

Also good example of Nature’s parsimony: once a useful structure has been developed, use it again and again. See also “Homology” example of vertebrate forelimbs.

EVIDENCE FOR EVOLUTION 4. Embryonic history

Fig. 3.8

EVIDENCE FOR EVOLUTION 5. Biogeography.

Ecological parallelism between Australian pouched mammals (marsupials) and placental mammal counterparts. Marsupials and placentals diverged over 100 Ma but similar ecological niches on different continents caused these very different groups of mammals to converge on similar body shapes.

This is a good example of environmental pressures steering evolution toward body types that can exploit the niche. Note that nature did not recreate the exact same body type, keeping with the rule-of-thumb that the same species has never been recreated.

Branching Organization of Life The Tree of Life: Another powerful

argument in favor of evolution

In Darwin’s time, the “tree of life” was deduced from anatomical similarities

In our time, DNA proves striking proof not only for the tree of life but also as a mechanism of evolution

Haeckel’s Evolutionary Tree

A tree-like representation by Ernst Haeckel, a nineteenth-century evolutionary biologist.

Ernst Heinrich Phillip August Haeckel, from The Evolution of Man (1879)

• http://www.learner.org/channel/courses/biology/archive/images/1198_d.html

STANDARD PHYLOGENTIC TREE

Human Fossil Bush The "Hominid

Family Bush" made up of modern humans, their ancestors, and their now-extinct relatives.

• http://www.learner.org/channel/courses/biology/archive/animations/stills/as_humev2.html

Five-kingdom vs. three-domain tree of life

The older five-kingdom tree of life, which has been replaced by Woese's three-domain tree.

• http://www.learner.org/channel/courses/biology/archive/images/1957.html

Tree of Life— Lateral Gene Transfer Diagram

Revised Tree of Life with all groups divided into their domains. Includes information about lateral gene transfer and the endosymbiosis of bacteria that became mitochondria and chloroplasts.http://www.learner.org/channel/courses/biology/archive/animations/stills/as_compev7.html

Chapter 3. Evolution

Charles Darwin & Natural Selection Evidence of evolution – the fossil

record Mechanism of evolution – DNA A modification - Punctuated

Equilibrium Creationism – a formidable

antagonist

DNA

Instructions that provide almost all of the information necessary for a living organism to grow and function are in the nucleus of every cell. These instructions tell the cell what role it will play in your body. The instructions are in the form of a molecule called deoxyribonucleic acid, or DNA . DNA is the chemical responsible for preserving, copying and transmitting information within cells and from generation to generation. In humans, the DNA molecule consists of two ribbon-like strands that wrap around each other, resembling a twisted ladder. This is often described as a double helix. DNA is contained in tightly coiled packets called chromosomes , found in the nucleus of every cell. Chromosomes consist of the double helix of DNA wrapped around proteins. The twisted ladder is made up of repeating units called nucleotides , each of which is a single building block...

What really happened …

Chapter 3. Evolution

Charles Darwin & Natural Selection Evidence of evolution – the fossil record Mechanism of evolution – DNA A modification - Punctuated

Equilibrium Creationism – a formidable opponent

Micro & Macro Evolution

Throughout most of the last century, researchers primarily focused on microevolution , which is slight genetic change over a few generations in a population.  Until recently, it was thought that these gradual changes from generation to generation indicated that past species regularly evolved gradually into other species over millions of years.  

This model of long term gradual change is usually referred to as phyletic gradualism.  It is essentially the 19th century Darwinian idea that species evolve slowly at a more or less steady rate.  A natural consequence of this sort of macroevolution would be the slow progressive change of one species into the next in a line.

phyletic gradualism(macroevolution)

Punctuated Equilibrium

In the early 1970's, Stephen J. Gould and Niles Eldredge argued that there is sufficient fossil evidence to show that some species remained essentially the same for millions of years and then underwent short periods of very rapid, major change.  Gould coined the term “punctuated equilibrium”

Punctuated equilibrium

Punctuated Equilibrium

The punctuated, or rapid change, periods were presumably the result of major environmental changes in predation pressure, food supply, climate, etc.  During these times, natural selection can favor varieties that were previously at a comparative disadvantage.  The result can be an accelerated rate of change in gene pool frequencies in the direction of the varieties that become the most favored by the new environmental conditions.  It would be expected that long droughts, major volcanic eruptions, and the beginning and ending of ice ages would be likely triggers for rapid evolution. 

Long periods of stability andshort episodes of change    

Origin of Species Where do new species come from?  That is

a key question that the biological sciences have been asking for more than 200 years.  Charles Darwin provided part of the answer in his explanation of natural selection.  The remainder came as a result of Gregor Mendel's experiments with basic genetic inheritance and the 20th century discoveries of the other natural processes that can cause evolution.  We now know that evolution can occur in two different patterns--adaptive radiation into multiple species and successive speciation within a single evolutionary line.

http://anthro.palomar.edu/synthetic/synth_9.htmhttp://anthro.palomar.edu/synthetic/synth_9.htm

Adaptive radiation

Adaptive radiation is the progressive diversification of a species into two or more species as groups adapt to different environments. 

Natural selection is usually the principle mechanism driving adaptive radiation. 

The initial step is the separation of a species into distinct breeding populations.  This usually happens as a result of geographic or social isolation.  Over time, the gene pools of the isolated populations diverge from each other by gradually acquiring different random mutations and sometimes as a result of random genetic drift.  When the populations are in dissimilar environments, environmental stresses are often not the same. 

Adaptive radiation

As a result, nature selects for As a result, nature selects for different traits existing within the gene different traits existing within the gene pools of the populations.  Over time, pools of the populations.  Over time, the populations genetically diverge the populations genetically diverge enough so that they can no longer enough so that they can no longer reproduce with each other.  At this reproduce with each other.  At this point, they have become separate point, they have become separate species and usually continue to species and usually continue to diverge in subsequent generations.  In diverge in subsequent generations.  In intermediate stages, the two newly or intermediate stages, the two newly or about to be separated species may be about to be separated species may be able to interbreed and produce able to interbreed and produce children, but most of them are likely to children, but most of them are likely to be sterile.  This is the case with the be sterile.  This is the case with the offspring of horses and donkeys--i.e., offspring of horses and donkeys--i.e., mules.  Eventually, however, species mules.  Eventually, however, species genetically diverge so much that they genetically diverge so much that they are unable to produce any children.  are unable to produce any children.  This is the case with sheep and cattle.This is the case with sheep and cattle.

successive speciation

The evolution of species by successive speciation occurs within a single evolutionary line without the branching of adaptive radiation.  This takes place when the members of a species consist of a single breeding population for many generations.  Descendant generations experience continuous spontaneous mutations and new directions of natural selection as the environment changes. 

This results in progressive changes in the gene pool frequencies of the population.   At any one time, all members of the population are the same species.  However, as generations subsequently replace each other, the gene pool is transformed--i.e., it evolves. 

Successive speciationSuccessive speciationwithin a single species linewithin a single species line

Eventually, the changes are great enough that if descendants could go back in time to mate with their distant ancestors, the genetic differences would prevent them from producing fertile offspring.  In other words, they would be different species.

Chapter 3. Evolution

Charles Darwin & Natural Selection Evidence of evolution – the fossil record Mechanism of evolution – DNA A modification - Punctuated Equilibrium Creationism – a formidable

opponent

Creationist History 1910-1915 A set of Christian tracts emerged in the US

which took a literalistic interpretation of Genesis (ex nihlo creation).

1920-1968 Evolution banned from public schools 1963 Creation Research Society, Institute for Creation

Research 1970-1980 "Equal Time" 1978-1995 "Balanced Treatment" 1996 "Evolution as Theory“ 2000 “Intelligent Design”

Notes on “theory “  Definition: [n]  a theory that explains scientific

observations; scientific theories must be falsifiable

A systematically organized body of knowledge applicable in a relatively wide variety of circumstances, especially a system of assumptions, accepted principles, and rules of procedure devised to analyze, predict, or otherwise explain the nature or behavior of a specified set of phenomena.

Abstract reasoning; speculation.

n 1: a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena; "theories can incorporate facts and laws and tested hypotheses"; "true in fact and theory"

2: a tentative theory about the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena; "a scientific hypothesis that survives experimental testing becomes a scientific theory";

theory

theory

A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.

Abstract reasoning; speculation: a decision based on experience rather than theory.

An assumption based on limited information or knowledge; a conjecture.