Chapter 16: Darwin’s Theory of Evolution

1. Chapter 16: Darwin’s Theory of Evolution Section 16-4: Evidence of Evolution

2. Biogeography • 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

3. The Age of the Earth and Fossils • 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

5. Recent Fossil Finds • History of life incomplete • Always more to learn • Evidence shows change

6. Comparing Anatomy and Embryology • 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

8. Comparing Anatomy and Embryology • Common structure = common descent, not common function • Body parts that share common function but not structure are analogous structures • Bee wing and bird wing

9. Comparing Anatomy and Embryology • 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

10. Comparing Anatomy and Embryology • Early developmental stages of many vertebrates look similar • Cells develop in the same order • Shows common ancestry

11. Genetics and Molecular Biology • Central dogma • Genetic code is universal – most organisms share the same genes • Shows common ancestry

12. Homologous Molecules • 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

13. Testing Natural Selection • 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

14. Evaluating Evolutionary Theory • 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