1. Genes and Variation
It’s an organism’s phenotype (traits) that make it better fit its environment
And these traits come from the alleles it has
All of the alleles in a population is known as its gene pool
Evolution is a change in the gene pool of a population over time.
This involves changes in allele frequency over time.

2. Sources of Variation
Random mutation…alleles can randomly change…we have approx 300 mutations from our parents, but most are unnoticeable.
Recombination…independent assortment and crossing over during meiosis make our genes different from our parents

3. Sources of Variation
Lateral gene transfer…genes transferred from 1 organism to another
e.g. bacteria often exchange DNA
not so much in higher organisms, like humans and most animals and plants

4. Phenotypes So it’s the phenotypes that we really see in evolution
Traits can be caused by 1 gene or many. Most are polygenic … controlled by many genes
So you don’t get just 2 phenotypes, like what we studied in genetic unit
Get a range of phenotypes, like we saw with bar graphs for height and hand size in human adaptation lab.

5. Bell Curves
With polygenic traits, you get this range of phenotypes rather than just 2
If this curve changes, evolution has occurred

6. 3 kinds of Natural Selection
Directional selection
Individuals at one end of curve are most fit for environment
e.g. birds with bigger beaks get more food

7. 3 kinds of Natural Selection
Stabilizing selection
Organisms with average trait survive best
e.g. babies with medium weights, too heavy or too light = health problems

8. 3 kinds of Natural Selection
Disruptive selection
Organism at both extremes are fittest
e.g. medium sized seeds less common, large and small beaks are advantageous

9. Genetic Drift So that’s how evolution occurs by Natural Selection
Can also occur by accident or chance and not by natural selection
Evolution by random chance is called genetic drift
Usually happens in smaller populations, because larger ones can recover from these accidents.

10. Genetic Drift Bottleneck effect
When an accident (e.g. disease, forest fire, hurricane) wipes out a large part of the population
the allele frequency may change, but not because of natural selection

11. Genetic Drift Founder effect
When a few individuals leave the group and start a new population
They may not have all the alleles in the original population, so the allele frequency has changed, but not because of natural selection

12. p = frequency of dominant allele q= frequency of recessive allele
Genetic Equilibrium
When a population isn’t evolving, it is in genetic equilibrium
Allele frequencies remain constant according to the Hardy-Weinberg Principle:
p + q = 1
p2 + 2pq + q2 = 1
p = frequency of dominant allele
q= frequency of recessive allele

13. Genetic Equilibrium
Hardy-Weinberg Principle predicts populations will stay in genetic equilibrium unless:
There is nonrandom mating (i.e. artificial or sexual selection, rather than natural selection)
Small population size (genetic drift has big effects, then)
Gene flow (alleles enter or leave the population through immigration (coming in) or emigration (leaving)

14. Genetic Equilibrium
Hardy-Weinberg Principle predicts populations will stay in genetic equilibrium unless:
Mutations happen to change the alleles available
Natural selection happens where one genotype becomes more fit for the environment, and survives to reproduce more often
H-W principle is kind of a “what if”. We know what it takes for evolution to occur, what would it take for evolution NOT to occur?

15. Speciation
A species is a population who members can interbreed and produce fertile offspring.
Evolution has occurred when 1 species is so different from another that they can’t mate any more.
This is called reproductive isolation

16. Kinds of Reproductive Isolation
Behavioral isolation
When organisms act differently and stop mating, e.g. birds in same area use different songs/rituals to attract mates
Temporal isolation
When organisms in the same area mate at different times from each other, e.g. orchids in rainforest blooming at different times, frogs in wetlands mating at different times

17. Besides Reproductive Isolation
Geographic Isolation
When a population is separated by a river, lake canyon, mountain and stop mating, e.g. Darwin’s finches on different islands, plant seeds that get carried to new areas

18. Example: Darwin’s Finches
Birds arrive from mainland onto islands (founder effect)
Birds travel to another island (geographic isolation)

19. Example: Darwin’s Finches
Changes in gene pool because of natural selection e.g. different seeds to eat = changes in beak size/shape; different plants = different colored feathers to hide/stand out

20. Example: Darwin’s Finches
Behavioral isolation: birds fly back, but are different now, don’t mate
Birds continue to compete, move around and evolve

21. Molecular clock
Very simply, by looking at how many differences there are in DNA, a biologist can tell how long ago the species evolved from each other.

22. Rates of Evolution Gradualism: very slowly with changes barely noticed
Punctuated equilibrium: short bursts followed by long time frames with no change

23. Kinds of Evolution Divergent evolution
What we’ve been talking about all along
One common ancestor leads to many descendants
Leads to homologous and vestigial structures

24. Kinds of Evolution Adaptive radiation
Evolve to inhabit all habitats and niches
e.g. dinosaurs…live on land, in water, in air, in swamps, herbivores, carnivores, etc.

25. Kinds of Evolution Convergent evolution
Organisms from different ancestors evolve to have similar traits
leads to analogous structures
e.g. grassland birds Darwin observed: ostrich, emu, rhea

26. Kinds of Evolution Coevolution
When organisms rely on each other so much that as one changes, the other does also
e.g. plants and the birds/ insects that pollinate them

27. Extinction If evolution doesn’t happen, species can go extinct:
Very slowly, a few species at a time = background extinction.
Relatively quickly, many species at once = mass extinction
5 mass extinctions in Earth’s history
Last one was 66 mya…dinosaurs
Biggest one was Permian...250mya…96% of all species wiped out!

29. Convergent Evolution

30. Divergent Evolution

31. Divergent Evolution

32. Adaptive Radiation
Evolve to fill many niches, e.g. live in many places or eat many different things

33. Adaptive Radiation