Hi, Andrew.
Welcome to EvC!
AndrewPD writes:
Therefore doesn't that mean that every species can only descend from one pair? Unless two identical species can evolve alongside one another. Unless I'm missing the point somewhere.
Yes, you're missing something.
Every pair of people comes from two pairs of other people, right?
So, your green-skinned kid came from one pair (you and your spouse), and your green-skinned kid's future spouse came from another pair. In turn, each of those four people came from another pair, each of whom also came from another pair.
Now, let's say I have a kid with pointy ears, like Spock. If my kid married your kid, they could have a pointy-eared, green-skinned baby. One trait came from your side, and one trait came from my side. The grandkid looks weird, but she is not a new species.
Then, let's say Dr Adequate's kid has six fingers. Somewhere along the line, one of his kid's descendants marries one of our pointy-eared, green-skinned grandkid's descendants, and we now have a six-fingered, pointy-eared, green-skinned person whose unique traits are traceable to three different original pairs.
Eventually, RAZD's and lyx2no's lineages get mixed in, etc., and the descendant has a fat nose, groucho eyebrows, vampire fangs, retractable fingernails, X-ray vision, six fingers, pointy ears and green skin. And, finally, they lose the ability to breed with normal humans, thus making them a new species.
So, just because one mutation comes from one pair, doesn't mean that the entirety of the species' genome comes from that one pair. Those traits accumulated from multiple pairs during a time when the carrier of the unique mutation could still interbreed with the "normal" population.
Edited by Bluejay, : "form" and "from" are not interchangeable
-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.
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