Natural Selection

Ok, here's the biggy.  The thing that everyone seems to argue about.  Charles Darwin's big theory that we're still fighting about almost 200 years later.

Natural selection is based on a couple of simple premises. The main premise is that individuals within a population have heritable differences that result in differential reproduction. The outcome of this is that those heritable differences that relatively increase the number of offspring from a given individual will be found in more and more individuals as time proceeds, as long as those heritable differences continue to have the same effect in response to the environment.

This is best explained by example, and I'm going to use the example of antibiotic resistance. Some bacteria contain genes that make them immune to the effects of certain antibiotics (antibiotics work by disrupting vital activities of bacteria). Let's say you have a strep infection, and some of those streptococcus bacteria in your throat have a gene for antibiotic resistance. You go to the doctor and get a prescription for penicillin. You take your antibiotics, and it kills all the streptococcus bacteria, except the ones that have the gene for antibiotic resistance. Now there are more antibiotic resistant bacteria in the environment. This seems pretty simple, right?

Well, when selective pressure is strong (if you'll die unless you have a certain difference in your DNA), it's easy to see how the concept works. It gets more complicated when the selective pressure isn't as strong. Let's get into that next time.