The Theory of Evolution by Natural Selection

1. The Theory of Evolution by Natural Selection Theory of Natural Selection 5 Key Observations Inferences In each generation, populations produce more offspring than there are adults Populations do not continue to grow in size. Individuals within a population compete for resources Over time the population changes as advantageous heritable characteristics become more common generation after generation. Food & many other resources are limited. Individuals within all populations vary. Some individuals will inherit characteristics that give them a better chance of surviving & reproducing Many variations are heritable.

2. What kinds of adaptations do these organisms have for their given environments?

3. Using the theory of natural selection, how can you now explain the evolution of the “stretched” Giraffe necks?

4. Evidence for Evolution:1) BIOGEOGRAPHY = The scientific study of the geographic distribution of organisms base don both living species and fossils. • Example: Remote islands (i.e. Galapagos) • Animals that live there exhibit unusual behaviours. • Many species are unusually fearless. • Darwin proposed that these species, living & evolving in a location with no natural predators, had lost their instinctive fear. • Species found here are found nowhere else, but many bear a resemblance to species on the nearest continental land mass.

5. Galapagos Islands (972 km west off the coast of Ecuador)

6. Darwin’s Observations in the Galapagos

7. Evidence for Evolution:2) HOMOLOGOUS FEATURES Homologous Feature = a structure with a common evolutionary origin that may serve different functions in modern species (ex. Human arm vs. Dolphin flipper).

8. Darwin was puzzled... “What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?” • Bones are even similar in their number and not just arrangement. • I.e. Almost all mammals have precisely 28 skull bones & 7 neck bones, regardless of the size of their skull or length of their necks.

9. Compare! Bat Human

10. Homologous features in embryos??? • Embryos of all vertebrates (i.e. Humans, chickens, fish) possess a short bony tail. • Human embryos also have gill slits even though by the time we are born, we do not have gills. • WHY? • - These species shared a common ancestor & over time, the original structures were modified as each species evolved.

11. Evidence for Evolution:3) ANALOGOUS FEATURES = A structure that performs the same function as another, but is not similar in origin or anatomical structure. - I.e. Wings of flying insects serve the same function as wings of flying birds, yet are completely different in structure (see below). WHY? - Insects & birds are only distantly related & have evolved these features independently of each other.

12. Evidence for Evolution:4) COMPARING DNA SEQUENCES Homologous Genes = genes inherited from a common ancestor that mutate and evolve over time. - The degree of similarity b/w homologous genes shows how closely related species are to one another.