Results of Evolution

1. Results of Evolution

2. Patterns of Evolution Evolution can result in changes that are small or large • Macroevolution: large evolutionary changes; usually takes a long time and occurs as the gradual accumulation of small changes (ex: Reptiles evolving into birds) • Microevolution: small evolutionary changes that occur faster and are easy to see within a lifetime (ex: the peppered moth changing color)

3. Macroevolution: Is it even Possible?

4. Patterns of Evolution Evolution can occur (relatively) quickly or it can be a slow process. • Gradualism: evolution as the slow accumulation of many small changes (ex – sharks today are basically the same as they were before the dinosaurs) • Punctuated Equilibrium: sudden change in a group after years of no change, result of STRONG selective pressure and/or big mutations (ex- mammals evolved very quickly to become large after the dinosaurs went extinct)

5. Results of Natural Selection

6. Results of Natural Selection Reminder: natural selection leads to changes in the GENE POOL of the GROUP

7. Results of Natural Selection Natural selection can change a population in three ways: 1. Directional Selection 2. Stabilizing Selection 3. Disruptive Selection

8. Results of Natural Selection Natural selection changes are based on bell curves. A bell curve shows the number of individuals within the group that have a particular trait. Since every individual is unique, some may have different versions of the trait. The highest point of the bell curve is the most common version of the trait in the group. Bell curves taper off in each direction as the variations on the trait become less common.

9. Directional Selection - One extreme is favored; individuals at one end of the curve have higher fitness than those in the middle/the other end- the entire curve shifts to the left or right as the extreme trait becomes more common

10. Directional Selection Example Generation after generation favored the largest of the horses. Over time, they gradually became larger and larger.

11. Stabilizing Selection - the average is favored; individuals near the center of the curve have higher fitness than individuals at either end- the center of the curve remains at its current position, but the graph narrows as the “sides” are eliminated

12. Stabilizing Selection Most human babies are between 7 and 9 pounds because babies smaller OR larger than that range have a higher risk of complications. Smaller babies typically have difficulty living outside of the mother (pre-mature birth). Large babies typically have difficulty being born.

13. Disruptive Selection - BOTH extremes are favored; individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle- being in the middle is bad in this case; population might split into two separate species given enough time.

14. Disruptive Selection Light and dark colored butterflies are better able to survive than medium colored butterflies in this species. Perhaps light can blend in with the light gray trees and dark can hide in the shadows while medium has no where to hide!

15. Divergent Evolution Disruptive Natural Selection often leads to… • divergent evolution: when two related groups develop more and more differences • examples: polar bear – white fur for camouflage grizzly bear – brown fur for camouflage • To “diverge” means to split apart

16. Convergent Evolution Careful! If two RELATED species can become more DIFFERENT, then two UNRELATED species can certainly become more SIMILAR if they live in the same environment • convergent evolution: when two UNRELATED species evolve similarities ONLY because they live in the same habitat and NOT because they are related (ex: sharks and dolphins)

17. Speciation

18. Speciation ANY of the natural selection patterns (directional, disruptive, or stabilizing) can change the group so much that they end up looking very different than their ancestors. At some point, they must be classified as a new species. The formation of a new species is called speciation. - Who or what defines a species? • Scientists decide when enough changes have occurred to re-categorize the organisms as a new species. • A species is generally defined as a group of similar organisms (plants, animals, fungi, cells, etc) that can successfully and naturally interbreed in the wild.

19. Isolating Mechanisms The key to maintaining a species is the ability to interbreed and keep the gene pool mixed. If something splits a group and stops them from interbreeding, then they will form separate gene pools and separate species. This is called reproductive isolation. 1. Behavioral Isolation – individuals are not attracted to one another (ex: different bird songs) 2. Geographic Isolation – individuals don’t live in the same area (ex: island species are separated from the mainland) 3. Temporal Isolation – the reproductive timing is off (ex: reproducing with the full moon instead of the half moon)

20. Behavioral Isolation Two populations are capable of interbreeding but have differences in courtship rituals or other types of behavior

21. Geographic Isolation Two populations are separated by geographic barriers (rivers, mountains, bodies of water)

22. Temporal Isolation Two or more species reproduce at different times

23. Temporal Isolation • Careful! Speciation can split a population into more than just two groups • Adaptive radiation: one ancestral group gives rise to many different species all at once (ex- Darwin’s finches evolved from the same ancestor, but were adapted to MANY different food sources resulting in more than just two species)

24. Organizing Evolution

25. Phylogenetic Trees • Tracing all the different pathways of evolution results in an image that looks similar to a tree • This phylogenetic tree of evolution must be created using ALL the evidence of evolution/relatedness we can find; the result is that the closer together two species are on the tree, the more closely related they are to each other • Try it: Who is the dog most closely related to?

26. Cladogram • Sometimes we don’t want to trace EVERYBODY’s path. Sometimes we just want to focus on a specific group and their similarities. This can be done through a cladogram. • Cladograms are based on derived (shared) characteristics only; only showing one type of evidence (like physical or DNA similarities); to read them, know that every species below the character lacks the trait while every species above the character has it • Try it: Who has dry skin, but no hair?