How Populations Evolve

How awesome was Charles Darwin?

So awesome. Like you wouldn't believe. He wrote the Origin of species. He proposed evolution in ways no one ever had before- generations upon generations of adaptation (Suck it, Lamark), using fossil and geological records (the church has nothing on this guy), and of course: the theory of natural selection.


What is natural selection?

Natural selection is the theory that those that have an advantage to life, such as a helpful mutation, will live, and thus will be able to pass this trait on to their offspring. Those that don't may or may not be less favorable for breeding, but if they are not because they do not possess this mutation, they will naturally die out or become less common.

What is the Hardy-Weinberg Equation?

p + q = 1

p^2  + 2pq + q^2 = 1

p = homozygous dominant
q = homozygous recessive
pq = heterozygous

The Facts:

-The Hardy-Weinberg equilibrium is the state in which evolution is static and the gene pool remains constant unless other factors are at work

-The Hardy-Weinberg equation only works if the population involved has 5 very specific criteria:

-1. Very large population

-2. No gene flow between populations
-3. No mutations

-4. Random Mating

-5. No natural selection

-A genetic drift is a change in the gene pool of a population due to chance, the smaller the population, the more impact the genetic drift will have

-The bottleneck effect refers to when a population is reduced down to very little, leaving only those that were most frequent, unless they had a trait that allowed them to survive the near-extinction

-The founder effect refers to when a few individuals colonize an island or new habitat and genetic drift takes place.

Some Key Terms:

-Adaptations: Inherited traits that enhance an organism's ability to live.

-Extinction: An irrevocable loss of species

-Fossil record: The sequence in which fossils appear in sedimentary rocks

-Strata: Layers

-Homology: Similarity in characteristics that results from a common ancestry

-Vestigial organs: Structures that are of marginal or perhaps no importance to the organism

-Mutation: A change in the nucleotide sequence

-Heterozygote advantage: Heterozygous organisms having greater reproductive success than homozygous

-Fitness: the contribution an individual makes to the gene pool of the next generation relative to that of others

-Sexual dimorphism: The secondary sexual characteristics that differ in males and females

Diagram:

Here you can see different colored marbles. Imagine the marbles are different species. In an event of mass death within this species, the most common (or most advantageous) will survive, albeit only a few of them. But we find in the next generation, there are only those genetically similar to those that survived, deteriorating the gene pool.

Summary:

This chapter was about the awesomeness of Darwin. Maybe not completely about him at all times, but it ties back to him a lot. First it talks about natural selection, which is just the process of the most desirable traits living on, and thus making for speedy evolution. It touches on how many animals probably had a common ancestor at one point, seeing as we have homologous structures to many of them. Although wings are a question, since they evolved in separate species in a different way. Then it talks about the Hardy-Weinberg equation, which is commonly used to gauge evolution in a population, since it rarely meets all the requirements.
It goes on to talk about sexual selection in animals, with sexual dimorphism and sexual selection. This means that the most genetically appealing (in a sense) will most likely attract mates.

A Cool Video:

http://www.youtube.com/watch?v=06hGNM9M6Fs