Dave Hone

You don't want to be the sexiest, toughest, biggest male, and you can only mate once.

All right, there's various cheats, but we won't get into that just yet.

You're only going to mate once, and you're going to put all your effort into helping rearing offspring rather than chasing down as many girls as possible.

Are you going to go for the biggest, fittest female as well, or are you going to go for the small, weedy one that doesn't look very well?

you go for the best one.

Well, how do you know that?

Well, cause she's got a crest as well.

And so suddenly you now get mutual ornamentation, just like the black swans, where the males are checking out the curliest females and the females are checking out the curliest males.

And you'll see they mutually pair up.

This is what we see with things like starlings.

Males like the brightest females.

Females like the brightest males.

They tend to form pairs.

The darkest and least bright ones are obviously kind of left with each other at the bottom of the pile.

They tend to pair up.

But it means that when you get signals in both males and females, like every triceratops or every tyrannosaurus, it at least hints that they're going down this route.

and that they might cooperate for reproduction.

Wow.

Yeah, and the problem is it's compromised by lots of things.

So that goes back to your earlier question about telling males from females apart.