1. EVOLUTION Relationships Among Organisms

2. Similarities Among Organisms All organisms on Earth are related Some relationships are easier to see than others – though most organisms have some similarity in body structure

3. Similarities Among Organisms

4. Common Descent Living things have slowly changed over time Each living species descended from other species over time Principle of common descent – all living things share common ancestors

5. Common Descent Anatomists discovered that when comparing adult animals with four limbs, similarities exist among the bones of the various types of arms and legs These are called homologous structures – have the same structure, but differ in function Means they come from common origin

7. Common Descent There are also embryological similarities Discovered vestigial organs – structures that seem to serve little or no purpose

8. Similarities Among Organisms Each species has a “tool kit” containing visible and invisible tools that perform essential survival functions Tool kits are the result of millions of years of evolution by natural selection It is easier to modify existing tool kits than to create entirely new ones

9. The Role of Chance Random change in population is called genetic drift Can be caused by migration, random mating differences These are changes that have nothing to do with natural selection

10. The Birth of New Species Speciation is the formation of new species. New population must change enough that breeding cannot occur with original population Genetic changes can be from mutations or natural selection, but must lead to reproductive isolation

11. The Birth of New Species Usually, speciation in plants and animals occurs when two groups of individuals become geographically isolated Darwin’s finches p. 251

12. The Pace of Evolution Gradualism is the view that evolution occurs slowly and steadily over long periods of time Punctuated equilibrium is the view that there are long periods of stability interrupted by episodes of rapid change.

13. The Pace of Evolution

14. Adaptive Radiation When a new species evolves in a relatively short period of time, or when an organism or a group of organisms colonizes a new area where other species compete for life’s necessities Results in a new tool kit Leads to homologous structures

15. Adaptive Radiation Sometimes called divergent evolution

16. Convergent Evolution Unrelated species may independently evolve superficial similarities because of adaptations to similar environments. Example: bats and birds both fly Leads to analogous structures – similar in appearance and function but develop from anatomically different parts

17. Homologous vs. Analogous Homologous structures – similar structure, different function Ex. arm of a human, wing of a bird Analogous structures – similar function, different structure Ex. bat wing, bird wing

18. Distant Relationships Looking at homologous structures, fossils, embryological similarities can show evolutionary relationships What about single celled organisms? Molecular similarities

19. Molecular Unity Many genes are shared by a wide range of organisms The same 20 amino acids make all proteins All cells need ribosomes – almost identical genes The more closely two organisms are related, the more closely their genes resemble each other

20. Muscle Proteins – in Yeast! Myosin is a protein found in muscle cells in animals – and yeast cells Yeasts do not move, so why do they need myosin? They use it to move products around within the cell