When cows are in heat, they mount their herdmates.

This is a great boon for farmers, as we can see when each cow is breedable by artificial insemination.

But I can’t figure out the evolutionary purpose. The bulls do not need a visual cue; they smell the vaginal discharge from a fair distance away.

It can be a dominance issue, because dominance games are played out at all times, not just when a particular cow is in heat.

I doubt that it is simply for pleasure. They pleasure we and Chimpanzees get from sex is largely to make the female receptive even when she is not likely to be impregnated, thus helping the man stick around and expend resources on his progeny (See Jared Diamond’s “Why Sex is Fun). Bulls contribute no resources to their progeny, and the cows are not receptive outside of the heat period.

Can anyone explain the Darwinian imperative that would have led this behavior become near-universal in the cattle population (I say near universal because some cows do not mount, having what we farmers call “silent heats”)?

Perhaps the behavior is ordained by the Flying Spaghetti Monster?

Seriously, I’m puzzled and I have stumped the science teachers at my school. Hopefully we count some renowned Darwinian behavioralists amongst our readership.