I did not know that is what the process was called. I now understand that introgression is gene flow, but instead of within a species it is between species.

What types of gene shuffling are there and how does that relate to natural selection?

How does functionalism fit into and relate to natural selection?

I thought the idea of gradualism was explained very well here. It is an important concept in evolution and shows how the process of change in a species can take time. For example a change in a species could be due to its environment.