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VOLUTION

Section 16-4: Evidence of Evolution

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HEORY

B IOGEOGRAPHY   

The study of where organisms live now and where they and their ancestors lived in the past

Patterns of distribution tell how modern organisms evolved from ancestors Two patterns important to Darwin:   Closely related but different – Galapagos species similar to mainland species, suggests natural selection caused variations Distantly related but similar – similar habitats can lead to similar adaptations in distantly related species

T HE A GE OF THE E ARTH AND F OSSILS       Hutton/Lyell argued Earth was old – but how old?

Modern geologists use radioactive dating to determine age of rocks/fossils Earth is about 4.5 billion years old Darwin’s study of fossils convinced him, but paleontologists had not yet found enough fossils of intermediate species Since then, many have been found Whales from ancient land mammals

R ECENT F OSSIL F INDS  History of life incomplete   Always more to learn Evidence shows change

C OMPARING A NATOMY AND E MBRYOLOGY      All vertebrate limbs have same basic bone structure Animals with similar structures evolved from common ancestor Homologous structures – same basic structure, shows common ancestry – different function Study anatomical details, development in embryos, pattern of appearance Similarities/differences show how recently organisms shared a common ancestor

C OMPARING A NATOMY AND E MBRYOLOGY    Common structure = common descent, not common function Body parts that share common function but not structure are analogous structures Bee wing and bird wing

C OMPARING A NATOMY AND E MBRYOLOGY    Vestigial structures – inherited from ancestors but have lost much of their original function Ex: hipbones of dolphins, wings of flightless birds Maybe presence of structure has no affect on fitness

C OMPARING A NATOMY AND E MBRYOLOGY    Early developmental stages of many vertebrates look similar Cells develop in the same order Shows common ancestry

G ENETICS AND M OLECULAR B IOLOGY  Central dogma   Genetic code is universal – most organisms share the same genes Shows common ancestry

H OMOLOGOUS M OLECULES    Homologous proteins share structural/chemical similarities Ex: Similar versions of cytochrome c (cellular respiration) found in all living cells Can also have homologous genes – Hox genes direct limb development  Minor changes in genes leads to major changes in structures

T ESTING N ATURAL S ELECTION  Gather evidence by observing it in action  Grants and the Galapagos finches (read in text!)  Showed competition and environmental change drive natural selection  Heritable variation the key – increased variation increases likelihood of adapting/surviving changes

E VALUATING E VOLUTIONARY T HEORY    Theory of evolution considered the grand unifying theory of the life sciences Constantly being reviewed as new data is gathered Questions that remain are about how evolution works, not whether it occurs