Xurtio

There's two dominant theories: 1) they were sexually selected, then naturally selected, and 2) they were always naturally selected.

The difference being that natural selection selects through killing animals not fit, while sexual selection selects through reducing (or demolishing) the ability of unfit animals to reproduce.

Edit: actually natural selection includes considerations of reproduction, but more mechanistically, while sexual selection comes down to (sometimes arbitrary) decision making on the part of the mate.

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