2. NATURAL SELECTION & EVIDENCE OF EVOLUTION Sections 10.3 & 10.4

3. Overview  Insights to Darwin’s Theory  Natural Selection & its principles  4 Means of Evolutionary Evidence

4. LETS REVIEW!  Define Evolution  Give me an example of a catastrophic event.  How do fossils help scientists link species?  What are examples of variations and adaptations?

5. Developing Darwin’s Natural Selection  20+ Years of Research & Investigation  Studied Animals & Plants  Examined the process of artificial selection in breeders.  Humans change a species by breeding it for certain traits.  Breed pigeons

6. Heritability  In order for artificial/natural selection to occur a trait must be heritable.  Heritability: ability of a trait to be passed down from one generation to the next.  Examples in pigeons: Tail feathers, neck feathers, crop.  Quick Question!  What kind of traits are not passed down?

7. Struggle for Survival  Idea Developed by Thomas Malthus  Populations are limited in growth by the abundance of resources (food, water, shelter, etc.)  Darwin expanded:  Variation & adaptation resulted in “descent with modification” Supply Offspring Demand

8. Natural Selection  Defined:  A mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.  Expand:  Advantageous characteristics result in survival and reproduction.  Analyze:  How long could this process take?

9. On the Origin of Species…  Darwin wrote a book depicting the four main principles of natural selection:  Variation  Overproduction  Adaptation  Descent with modification

10. Variation  The basis for natural selection.  Differences in individuals results from differences in genetic material.  Inherited or mutations

11. Overproduction  Increased offspring = Increased chance for some to survive  Results in competition for resources

12. Adaptation  Certain variations increase chances of survival over others in its environment.

13. Descent with Modification  Over time, adaptations found beneficial to survival and reproduction become more abundant in the population.  Leads to future generations having that trait.  As long as environmental conditions remain, trait will remain beneficial.

14. Adaptations as Compromise  Misconception:  Natural selection means that individuals become perfection suited for their environment.  Reality:  Some structures never change but do change in their role.  Panda bears wrist bone acts as a “thumb” Never physically changed the bones function, just its size.

15. Fast Brain Break  Researchers recently found a new species of spider and named it “Darwin bark spider”  This spider spins web 10 times stronger than Kevlar that are the width of some rivers.  Scientists are still studying how it can possibly make webs this large.

16. Evidence of Evolution  Darwin found multiple different forms of evidence:  Fossils  Geography  Embryology  Anatomy

17. Fossils  Earlier scientists noticed changes in rock stratum had changes in the types of fossils.  Later studies proved that the age of fossils was different in these layers.  Supports descent with modification.

18. Geography  Galapagos Island’s  Migration  Differing ecosystems on the islands leads to different traits in the same species.  Finches  All share same ancestor from mainland South America

19. Embryology  Similar features in embryos in very different organisms suggests evolution from a distant common ancestor.  Crab vs. Barnacle larvae

21. Anatomy  Evidence based on comparing body parts of different species.  Homologous structures:  Features similar in structure but appear in different organisms and have different functions.  Why would different groups of animals share similar structures?  Similar structures does not prove close relationship.  Some structures found in different species evolved from different ancestors.

22. Anatomy – Homologous Structures

23. Anatomy – Analogous Structures  Define:  Structures that perform similar function but are not similar in origin.  Discuss:  Not evidence of common ancestor.  Expand:  What are some examples?

24. Anatomy – Analogous Structures

25. Anatomy – Vestigal structures  Remnants of organs or structures that had function in an early ancestor.