Pal Chap 5 Evolution

7/30/2019 Pal Chap 5 Evolution

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EVOLUTION

The Principle of Evolution

z Living things have evolved through time in anorderly fashion, without repetition and withoutreversal, to produce modern life. OR

z All existing life has its origins in pre-existing

life and has changed to its present state

through successive generations.


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Contributing Concepts

to Evolution

z Lucretius 96-55 BC

Universe-shower of atoms with eddies

Nature in a constant state of change, growth,deathspecies change with time

z Read by scholars in spite of conflict withBible

z Note conflict with Creationists universemade all at once then decay

Concepts Contributing to Darwin'sEvolution

z Exploration of the world in 1700s

World too large for biblical accounts

Too many animals for the ark

Animals (and plants) differ markedly in different parts of the

world

z

Linneuss books Huge number of living things

Living things are naturally related to one another


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Contributing Concepts

to Evolution

z Geology William Smith

z Studied fossils of England

z Developed the Law of Fossil Succession

Fossils succeed one another in an orderly fashionthrough time

New forms appear as time passes not all atonce

Flood (s) dont explain it


z Geology

James Hutton and Charles Lyell

Geologic Time and Uniformitarianism

z The earth is very, very old (more than 6000 yrs.)

z Present day processes explain past changes in rocks

(and fossils)


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Concepts Contributing to Darwin's

Evolution

Count Buffon (1707-1788)

The Ladder of Creation Theorized thetransmutation of species into one another

Simple to complex with man at top but belowangels and God.

Still accepted by some; was accepted by

Thomas Jefferson

Ladder of Creation

z Depends on spontaneous generation

z Each group evolves parallel to others

z Problems:

Fossil record not a picture of simple to complex

Cambrian Explosion Spontaneous generation disproved by Louis

Pasteur


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Evolution

z Jean Baptiste Lamark (1744-1829) Inheritance of acquired characteristics

Characteristics acquired during organismslifetime can be passed on, inherited.

Life evolved by accumulation of

acquired characters

Inheritance of AcquiredCharacteristics

z Problems

August Weismann (1834-1914 experimentsproved it isnt so with mice

James Watson (1928-) described a one-wayrelationship between DNA and RNA


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Evolution

z Georges Cuvier (1769-1832)

z Catastrophism: Catastrophies explained extinctionsand new creations

z Unconformities were evidence of catastrophies

z Problems:

Extinctions didnt always correspond to unconformities New forms arose between unconformities


z Erasmus Darwin (1731-1802)

z Poem on Evolution

Evolution of all life from a singleancestor

Like a branching tree

z Problem

Lacking a mechanism for speciation


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Concepts Contributing to Darwins

Evolution

z Thomas Malthus (1766-1834)

Many more are born than survive

Individuals in a population compete forlimited resources

Evolution by Means of NaturalSelection

Alfred Russel Wallace(1823-1913)

Charles Darwin (1809-1882)


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Darwins Evidence in Origin of

Species

z Domestic selective breeding

z Natural adaptation to the environment

z Natural variation within populations

z Malthusian population and competition

z Fossils

z

Geographic distribution of speciesz Linnaeuss taxonomy

Darwins Evidence

z Domestic animals and selective breeding

Produces new forms like new varieties

The boundaries between varieties and speciesare blurred.


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Darwins Evidence

z Adaptation to the environment

Animals are physically and behaviorally adaptedto their immediate environments

Darwins finches

Diversification of

island life

Darwins evidence

z Variation within Populations Variations occur in all species

The boundary between species, sub-species andvarieties is blurred

Variations can be selected for (as in domesticselective breeding)

Variations become species in islands bydiversification into different environments

Variations can become new species characters


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Darwins Evidence

z Many more are born than survive

Competition must determine which survive

z Fossil Records show species arising andbecoming extinct (although imperfect recordof gradual change)

Darwins Evidence

z Geographic distribution

Species in proximity show closer relationships to each other

than to more geographically distant relatives.

Islands near continents are populated with species closelyrelated to those on the adjacent continent

Species are not randomly distributed around the world as a

creator would have made them


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Darwins Evidence

z The natural system of classification (Linneantaxonomy) reflects a belief in descent.

Genera and Families imply that their membersare descended from common ancestors (acommon ancestor)

Evolution is an underlying principle of taxonomy

Darwins Conclusions

z Natural Selection

z Evolution

z Phyletic Gradualism

z Cladism

z Competition


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Darwins Conclusions

z Natural Selection Organisms that inherit favorablevariations for their immediate environment will tendto survive more often than others (and reproduce). Traits appear in a population

Nature selectively acts on individuals with that trait todestroy or perpetuate

If favorable, trait spreads to whole population making achange toward new variety or species

Traits add up

Darwins Conclusions

z Evolution

Life has changed constantly through time

New species have arisen and species havebecome extinct

This occurs because of natural selection acting on

variations within populations


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Darwins Conclusions

z Phyletic Gradualism

The change from one species to another is agradual process

If change in the fossil record seems abrupt it isbecause the record is so imperfect.

Darwins Conclusions

z Cladism

Similar organisms aredescended from a singleancestor

Evolution is like a branching

tree


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Neodarwinism

z Mutation Changes in the genotype that produce changes in

the phenotype

Most mutations are detrimental to the phenotype,but not all.

z Population Genetics Mathematics show natural selection could make

major changes in the gene pool even with lowrates of mutation.

The 4 ISMs of Neodarwinism

z Reductionism

z Panselectionism

z Extrapolationism

z Gradualism


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Panselectionism

z While recognizing the importance of random drift forsilent mutations, selectionists hypotheses arguethat balancing and positive selection are the drivingforces of molecular evolution. Those hypotheses areoften based on the broader view calledpanselectionism, the idea that selection is the onlyforce strong enough to explain evolution, relaying

random drift and mutations to minor roles.

Panselectionism

z Natural selection is a continuously operatingforce that acts on all traits of the phenotype(hence all genes)


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Panselectionism

z All changes in the population are adaptive insome way

z All traits of the species are adaptive in someway

Panselectionism

z Nothing is neutral or wasted

The lions archetypal roar is used to communicate withother group members and warn intruders of territorial

boundaries.Long, retractable claws help the lion to grab and hold

prey.The species rough tongue helps it to peel the skin ofprey animals away from flesh and flesh away from

bone.Loose belly skin allows the African lion to be kicked by

prey with little chance of injury.


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Extrapolationism

z Part of Microevolution

Small changes seen in modern populations (suchas fruit flies) can be extrapolated to explain allmajor evolutionary change

Small changes add up to create larger changes

Microevolution is evolution on a small scalewithin asingle population. That means narrowing our focus toone branch of the tree of life.

Extrapolationism

z Microevolution


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Phyletic Gradualism

z Phyletic gradualism is a speciationhypothesis rooted in uniformitarianism. Thehypothesis states that species continue toadapt to new environmental and biologicalselection pressures over the course of theirhistory, gradually becoming new species

Gradualism

z Part of Microevolution

Evolution takes place gradually by theaccumulation of small steps that add up to largerchanges.

Numerous transitional stages should be

observable in evolution from one species toanother


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Gradualism: A long time ago, there were a lot of tiger-like animals, but withoutstripes. Most of them were unmarked, but a few had light markings and color

variation in their fur. These few blended in with the tall grasses a little bit better,so they were generally able to catch more food, and fewer of the marked than

unmarked ones died of hunger, so more of them were able to reproduce. In thenext generation, more animals were marked than in the previous generation. Ofthose that were marked, some had more, some less, and some the same amountof marks than in the previous generation. Also, the marks were more, less, or thesame amount clearly defined. Again, the ones with marks did better than the ones

without, and the ones with more, clearly defined marks did better than the oneswith fewer or fainter marks. Very gradually, over many, many generations, stripes

over the tigers' whole bodies formed and appeared in the whole population,because the tigers that survived in each generation were those whose marks weremost clear and contrasted most with the rest of the fur, and those that covered the

most area on the bodies of the tigers.

Challenges to Neodarwinism

z New Lamarkian Ideas

z Neutralism

z Types of Strange Genes

z Macroevolution

z Evolution and Paleontologyz New Theory of Evolution Punctuated

Equilibrium


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New Lamarkian Ideas

z Genetic assimilation shock orenvironmental stimulus seems to causegenetic change

z Experiential genes immunity inheritance

z Jumping genes and viruses

Jumping genes

z Transposons are sequences of DNA that can movearound to different positions within the genome of asingle cell, a process called transposition. In theprocess, they can cause mutations and change theamount of DNA in the genome. Transposons werealso once called jumping genes, and are examplesof mobile genetic elements. They were discovered

by Barbara McClintock early in her career, for whichshe was awarded a Nobel prize in 1983.


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Neutralism

z The neutral theory of molecular evolutionwas introduced by Motoo Kimura in the late1960s and early 1970s. The theory statesthat the vast majority of evolutionary changesat the molecular level are caused by randomdrift of selectively neutral mutants.

Neutralism

z Many genes never used (cant be subject toselection)

z Both genes and mutations (selectivelyneutral) can accumulate for large changes

z Pleiotropy Genes that code for multiple

features- some features carried along


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Types of Strange Genes

z Quantitative Inheritance

Eg. Weight/height depends on several Genes

AABBCCDD-biggest

aabbccdd- smallest

AAbbCCdd in between

Types of Strange Genes

z Structural genes and regulatory genes-regulatory genes control many structuralgenes so change in reg. means manychanges in structure.

z Junk genes dont seem to do anything

z Homeotic genes make major changes limb in wrong place


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Macroevolution

z Robert Goldschmidt

Structural and regulatory genes

Macroevolution and the hopeful monster- theproblem of a mate

Breakthroughs in embryology change can takeplace in several individuals

Evolution and Paleontology

z G. G. Simpson gradualism in the fossilrecord

z Biostratigraphy Practitioners used stasis inthe fossil record

z

Eldrich and Gould Species are inflexibleand non-responsive to the environment

z Sewall Wright Species are a heirarchicallevel above individuals and populations.


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Evolution and Paleontology

z Species Sorting

Does natural selection work on species?

Competition is between species (not individuals?)

Extinction

Species speciate, not organisms

A new theory of evolution

z Macroevolution

z Allopatric Speciation

z Punctuated Equilibrium

z Species sorting


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Answers to the isms

z Reductionism neither the individual nor thespecies is merely the sum of its genes

z Panselectionism some changes are neutralto selection; many of such changes are pre-adaptive

Answers to isms

z Extrapolationism small changes do not addup. Small changes are irrelevant; speciationrequires large changes

z Gradualism Species are static. They do

not change gradually. New species appear

fully formed, abruptly.

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Pal Chap 5 Evolution