Well, evolution is a good guess, but not the right one. Although your approach is very good, and in line with the right answer, you’re still overthinking it. All the pics have 1 thing in common, that’s all you need to find.
To make it easier (or maybe harder, who knows?), here’s a final set of pics with the same thing in common.
You now have 13 pics with 1 thing in common. Can you guess it?