That's all fine, and doesn't matter if I agree or not, just make sure you give a full explanation of everything you might even think I might not be aware of. Judging from some of the accusations here, I'm sure you want me to understand the science before I proceed, so make me understand. If I have a problem with something, I'll certainly let you know what and why.
The theory of evolution explains the observation that the frequency of alleles in a population changes over time with these 4 mechanisms:
1. Natural selection: is the idea that certain inheritable traits allow some members of the population to live longer and/or produce more offspring in response to the environment they live in. This can be accomplished in several different ways. A trait might give some members of the population an advantage in dealing with cold weather (thicker pelts, for example), or allow them to be more appealing to the opposite gender (more colorful plumage, for example), or keep them hidden or better able to fight off predators (skin/fur color, for example). So basically, the individuals who possess these traits become more prevalent within their community over time, because they reproduce at a higher rate; fewer are killed off before reproducing, or more mates are found, producing babies at a higher rate.
Many studies have been done both in the lab, and in nature to test whether this effect indeed has an effect in proliferating those traits. Results confirm the mechanism. Additionally, the effect can be manufactured and enhanced artificially by purposely introducing an environmental pressure that the population has to deal with.
2. Mutation: is the mechanism by which traits arise, by causing a variant of a particular gene (an allele), which is sometimes expressed phenotypically (changed characteristics or traits). For example, blue eyes are a result of a mutation which limits the melanin produced in the iris of the eye. Germ line mutations are mutations that are passed on to successive generations (as opposed to somatic mutations), and it is these mutations which effect the frequency in which they succeed (or fail) within a population.
Though mutations happen randomly, the rate at which they spread through a population is
usually (see genetic drift) not random due to the fact that once they do occur, natural selection acts upon it making it more or less likely that the organisms with the mutation reproduce successfully.
3. Genetic drift: sometimes a trait arises which does not necessarily give the organism a better or worse chance of surviving and reproducing, yet still proliferates within the population. This typically happens more in small populations, since it is easier for a trait to spread throughout the smaller number of individuals. Basically, these are just "lucky" traits that happen to spread throughout the population, due to the fact that the organisms with these traits reproduced more frequently, either due to existing along side other traits which act normally under natural selection, or, as in the case with bottle necks, the lack of diverse mating options.
4. Gene flow: describes the transfer of genes which are passed on from one population to another. For example, pollen from one population of a plant can be transported long distances interacting with a different population.
If there is a high rate of gene flow between populations, then this hinders the divergence between the two populations, as the arisen traits in each population are shared with each other. Likewise, a low rate of gene transfer will gradually cause the populations to further diverge, as new traits are not shared between them.
Horizontal gene transfer is when genes are shared asexually. For example, through introduction by viruses, or conjugation which is where bacteria which come in to contact share genetic material.
