AP Biology 2006-2007

Chapter 15.3

Evidence of Evolution

Dodo bird

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Fossil Record The fossil record is incomplete but provides

some evidence about the history of the earth. Fossils can show the progression of ancient,

primitive organisms to modern day forms.Trilobite Leaf

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Fossil Record: The history of life on Earth can be partially constructed by dating (age) and comparing fossils

- Relative Dating: approximate age based on position on the rock layers

- Absolute Dating: Exact age determined by radioactive dating

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Extinct: Trilobite (crustacean) Ammonite (mollusc)

Similar to present-day species: still aroundFish Scallop (mollusc)

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Comparative AnatomyA. Homologous structures: Homologous

structures develop from the same tissues, but have different forms with different functions.

Same origin -- different form/function

The similarity is due to having derived from the same common ancestor.

Example: Bone structure of arms and legs in all vertebrates.

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B. Analogous Structures: Different origin but have similar function

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Vestigial structures Modern animals may have structures

that serve little or no function remnants of structures that were

functional in ancestral species evidence of change over time

some snakes & whales show remains of the pelvis & leg bones of walking ancestors

eyes on blind cave fish

human tail bone

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Hind leg bones on whale fossils

Why would whales have pelvis & leg bones if they were always sea creatures?

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Comparative embryology Similar embryological development in

closely related species all vertebrate embryos have a gill pouch

at one stage of development fish, frog, snake, birds, human, etc.

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Molecular record Comparing DNA & protein structure

universal genetic code! DNA & RNA

cytochrome C (respiration) protein structure

hemoglobin (gas exchange) protein structure

Evolutionary relationships among species are documented in their DNA & proteins.Closely related species have sequences that are more similar than distantly related species.

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Comparative hemoglobin structure

Number of amino acid differences betweenhemoglobin (146 aa) of vertebrate species and that of humans

Number of amino acid differences betweenhemoglobin (146 aa) of vertebrate species and that of humans

100 20 30 40 50 60 70 80 90 100 110 120

LampreyFrogBirdDogMacaqueHuman

328 45 67 125

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Building “family” treesClosely related species (twigs of tree) share same line of descent until their recent divergence from a common ancestor

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VIEW: http://www.pbs.org/wgbh/evolution/library/07/3/real/l_073_47.html

What data from whole genome sequencing can tell us about evolution of humans

What data from whole genome sequencing can tell us about evolution of humans

• Macroevolution – evolution on a large scale (above population level)

How fast is evolution?How fast do organisms change?

Gradualism Punctuated Equilibrium

Gradualism• Organisms go through gradual and continuous

change

Punctuated Equilibrium• Organisms go through fast periods of change,

followed by long periods of no change (according to fossil record)

Gradualism Punctuated Equilibrium

Patterns of Evolution: 1. Convergent Evolution

• Convergent Evolution: When 2 or more unrelated species become more similar due to similar adaptations to their environment.

Convergent evolution• Flight evolved 3 separate times

– evolving similar solutions to similar “problems”

• Divergent Evolution: when related species become more different as they adapt to different environments

• Divergent evolution leads to Adaptive Radiation

Patterns of Evolution: 2. Divergent Evolution-Adaptive Radiation

Adaptive Radiation• Process by which a

single species or small group of species evolved into several different forms that live in different ways

Coevolution• Predator-prey relationships• Parasite-host relationships• Flowers & pollinators

Process by which two species evolve in response to each other over time