EvolutionA process of change through time

Charles Darwin

First Scientist to study evolution on the Galapagos Islands

Aboard the HMS BeagleDecember 1831 to October 1836

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Evolution

• Biological evolution, simply put, is descent with modification. – This definition encompasses small-scale evolution

– As well as large-scale evolution

Natural Selection

• Populations change in response to their environment.

• Acts on phenotype of an organism.

(Not genotype)

Theories of Evolution

Jeane Babtiste LamarkThe Principle of Use and Disuse:New structures developed in anorganism during the course ofevolution because they were needed and unused structureswere lost.

Inheritance of Acquired Characteristics: Characteristics During a lifetime were passed onto offspring.

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STUDY QUESTIONS

• Why do some organisms become extinct?

• What defines a species?

• How do selective forces guide evolution?

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On the Origin of Species, published on 24 November 1859

http://anthro.palomar.edu/evolve/evolve_2.htm

Evolution occurs because of Natural Selection, with nature acting as the selecting agent.

Organisms better adaptedto the environment surviveand reproduce moresuccessfully than less-welladapted organisms.

Speciation

• Formation of a new species

Reproductive Isolation Separation of two groups over a long period of time mayResult in change in the genetic makeup of the two groups Making them unable to reproduce with each other.

Geographic IsolationA body of water or mountain range separates a population of a speciesresulting in evolution of new species.

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EVIDENCE OF EVOLUTION

Geological Record: Through radioactive dating the oldest rocks in the earth’s crust, the age of the earth is 4.5 – 5 billion years old.

Fossils: Traces of once living organisms

In Rock

In Amber In Ice

Petrifaction

Comparative Anatomy: Organism with similar bodyStructure evolved along the same line.

Homologous Structures: Evidence of common ancestry.

AnalogousStructures : Same function, structurallydifferent. Show no common ancestry.

Vestigial Structures: Structures in an organism through evolution have been lost or reduced in size because they wereno longer necessary trait for survival.

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Mustard Evidence

http://evolution.berkeley.edu/evolibrary/home.php

Embryology

http://evolution.berkeley.edu/evolibrary/home.php

Bacterial Antibiotic Resistance

Modern Theories of EvolutionA change in the DNA of an organism over a period of time

Sources of variation

Sexual Reproduction: A recombination of alleles.

Random and spontaneous gene and chromosome mutations.

Natural Selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift. Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood.

To find out how it works, imagine a population of beetles:

There is variation in traits.For example, some beetles are green and some are brown.

There is differential reproduction.Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

There is heredity.The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

End result:The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.

If you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome. It is as simple as that.

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Chromosome numbers in the great apes:

human (Homo) 4646chimpanzee (Pan) 48gorilla (Gorilla) 48orangutan (Pogo) 48

Testing the Evolutionary Hypothesis of Common Ancestry

Testable prediction:Testable prediction: If these organisms share common ancestry, the human genome must contain a fused chromosome.

Testing the Evolutionary Hypothesis of Common Ancestry

Chromosome numbers in the great apes (Hominidae):

human (Homo) 4646chimpanzee (Pan) 48gorilla (Gorilla) 48orangutan (Pogo) 48

Testable prediction:Testable prediction: The marks of that fusion must appear in one of the human chromosomes.

Centromere

Telomere

Ancestral Chromosomes

Fusion

Homo sapiens

Centromere #1

Telomere sequences

Centromere #2

Homo sapiens

centromere #13 (inactive)

Telomere sequences

Human Chromosome #2 shows the exact point at which this fusion took place

centromere #12 (active)

Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724-731.

“There is grandeur in this view of life; with its several powers having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most wonderful and most beautiful have been, and are being evolved.”

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Why not?

Because these structures possess “Irreducible Complexity,” and that means they could not have been produced by evolution — even in principle.

Biochemical Claim: Evolution cannot explain the origin of Complex Cellular Machines

Prime Example• Bacterial flagellum

Bacterial Flagellum

Electron micrograph of an E. coli showing several flagella

at the apex of the cell.

The complete machine has a

function...

....but its component parts do not.

Bacterial Flagellum

The complete machine has a

function...

“Since natural selection requires a function to select, an irreducibly complex biological system ... would have to arise as an integrated unit for natural selection to have anything to act on.”

No function. Therefore, natural selection cannot shape components.

Individual Parts

Function Favored by Natural Selection

No function. Therefore, natural selection cannot shape components.

BiochemicalMachine

Individual Parts

Individual Parts

Components originate with different functions.

BiochemicalMachine

New functions emergefrom combinations of

components.

BiochemicalMachine

“Irreducible Complexity” makes a specific claim, and so does evolution.

DESIGN:

Parts useless on their own

EVOLUTION:

Parts do other jobs

Therefore, if we take away 40 of the flagellum’s parts:

Leaving just 10. What’s left should be non-functional. Right?

But they’re not!

Type-III Secretory System(10 parts)

Bacterial Flagellum(~50 parts)

“...any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional.”

But it’s not. In fact, those 10 parts are fully-functional!

REFERENCES

• Biology: The Dynamics of Life; Glencoe 2004

• http://evolution.berkeley.edu/evolibrary/home.php

• http://www.hhmi.org/biointeractive/evolution/index.html

• http://www.accessexcellence.org/AE/AEPC/WWC/1995/

• http://www.darwinday.org/englishL/life/beagle.html

• http://www.pbs.org/wgbh/evolution/index.html

• DR. LUE, LIFE SCIENCE-HHMI OUTREACH PPT.

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.