What is evolution?

I've argued against evolution - or more precisely I've argued against certain components of evolution - on many occasions. I use evolution to mean Darwinism or rather neo-Darwinism which is the mainstream theory of evolution today.

That said, oftentimes debates over evolution forget the very basics. They often forget to define what evolution is in the first place. So I'll try to do that now in a hopefully simple manner accessible to most people reading this.

What is evolution? Evolution is the combination of six components:

1. Genetic change over time. A species undergoes change in their genes or alleles over time. (Alleles are simply variants of the same gene.)
2. Gradualism. It takes a long time (generations) to produce genetic change.
3. Speciation. The simple idea is splitting. One or more species can split off from another species.
4. Common ancestry. This is the flipside of speciation. If species can split off from other species, then we can trace the splitting back in time (via fossils and genetic sequences) to find the shared or common ancestor of two or more species.
5. Natural selection. Organisms in the same species may have genetic differences among one another. This in turn impacts their ability to reproduce and survive in an environment. The genes that are more conducive to reproduction and survival will more likely be passed on (heredity) to the subsequent generation while the genes that don't will be less likely to be passed on (heredity) to the subsequent generation. That's in essence what natural selection is.
6. Other mechanisms (besides natural selection). These include genetic drift, gene flow, and random genetic mutations which can cause evolutionary change. The primary mechanism (especially in a large population) is random genetic mutations. Broadly speaking, random genetic mutations are permanent alterations in a gene.

This is a fairly standard definition of evolution. In fact, it's so standard that it's based in large part on Jerry Coyne's Why Evolution Is True!

Now that we have a mainstream working definition, we can begin to voice our concerns and disagreements with evolution (neo-Darwinism). Keeping this in mind, see my earlier post including its comments for many of my own thoughts on evolution.