Okay, in layman's terms, explain to my dimwhitted self exactly how does evolution occur from an evolutionists point of view. Don't give me a ton of links either. We should have a minimum of 5 links rule or something. I have tried to link specifically relevant articles and have often been thrown hundreds of links at a time and then been complained about because I did not answer the post.
OK. Evolution (in biology) means that a population changes over time. This change happens during the reproduction process of the individuals this population consists of. So you get offspring that has a mix of its parents genetic material plus some mutations which always occur to some extent. Some of these new configurations can produce individuals that are better suited to their environment than their parents or their siblings, so they have higher chances to procreate and on average they also have more offspring.
Over time the genetic makeup of this population can change considerably. So if you had a specimen from the current population and one from the ancestor population and compared them, it can make sense to assign them to two different species.
Of course a population can also split up, and the two (or more) groups get reproductively isolated. This means that changes that arise in one group are no longer shared with the other group(s). Usually these subpopulations are exposed to different environmental conditions which means that natural selection affects them in different ways.
If they stay isolated long enough, it can happen that they changed so much that they don't recognize each other as potential mates. This can be nicely observed in
ring species where the two populations at the end of the 'ring' don't recognize each other (
here is a nice illustration of a warbler ring species).
