Dave Hone

So anyone who keeps little fish, if anyone's who's a tropical fish keeper, swordtails are really quite common little tropical fish that you can get in all kinds of aquarium shops.

And they're a very boring fish shape, but the lower lobe of their tail has a big spike on it.

And that's the name.

And they're really close relatives of a group called the Mollies, which basically don't have that.

And in the wild, these are Amazonian fish.

They don't usually encounter each other.

But even if you go and get not even the domesticated form, because these things have been bred for decades at this point, you can go and get some wild Mollies and give them a wild male swordtail.

And they think he's so much better than all the male Mollies.

They will go for that one and they will preferentially mate with that one.

We don't know the exact mechanism, but it appears to be it looks similar enough that I recognize it as a potential mate, but different enough that this is exciting.

And then this is where the sexy sons kick in because the females are now assuming those animals are successful and they can hybridize.

Or maybe it's just a male who just happens to be a little bit blue or a little bit red or whatever it may be.

Um, well, the female offspring, the daughters are probably going to inherit mother's preference.

I really like red and the males are probably going to have red in them because their dad had more red.

So guess what the next generation does?

It's more red and the females like more red and you don't have to come back much further.

And suddenly all the males are bright red.

And that's closer to beauty than I think almost anything else would be with still a naturalistic explanation.

Yeah, a T-Rex might have.

So the very fact that they have these apparently socio-sexually selected signals, the little crest and stuff in the head...