[vhawk01]

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Yes, please explain to me how birds, reptiles, and primates are not different from one another.

If you tell me it's because they're all made up of G's T's C's and A's, you're not going to win any points.

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Oh, they are definitely different. Just as a heap and a grain of sand are different. But there was never a first heap, and there was never a first bird. The point is, we call them "birds" and "primates" based on their endpoints. These endpoints are very easy to distinguish from each other, because they are thousands/millions of generations apart. The point is, if we had followed them, generation to generation, there would never have been an animal that we would call a BIRD and one we would call a REPTILE sitting next to each other. Just as, if we add one grain of sand at a time, there is never a point where we say "NOW this is a heap."

As RDuke mentioned, ring species are fascinating and illustrate this as well, but we'll see what questions you have with this first before moving on.