Name: The first round.

Age: As old as pubs.

Appearance: A necessity of evolutionary biology.

Buying a pint is a necessity of evolutionary biology? No, but buying lots of pints is. Let me ask you a question. How quickly do you offer to get the first round in when you enter a pub?

Very slowly. Have you seen the price of beer lately? What if you were the sole male in a group of females?

Even slower. They’d all want cocktails and I’d be at the bar for ever, and the bartender would hate me, and it would bankrupt me. Bit sexist, but we’ll let it slide. Now, what if there were loads of men and only a few women in the group?

I’d be straight to the bar like a shot. Interesting. And why is that?

I don’t know. It’s like a deep, involuntary genetic compulsion. It’s evolutionary biology.

What? You’re competing for access to the women in the group. By rushing to the bar first, you’re demonstrating to them that you have available resources.

I’d need them to afford six drinks in a pub in 2024. This is what biologists call the “adult sex ratio”. If there are more men than women, then the men compete to look the most desirable.

Is this real? It’s absurdly real. A team of researchers from Harvard University spent time in three Boston pubs, watching 160 groups of customers. The behaviour was so uniform that they could eventually predict it. If a group had more men than women, a man would race to the bar within seconds to get drinks for everyone. But if it had more women than men, it would take significantly longer to get a round in.

And when did the women get the first drinks in? Never. They never did.

Why do men do this? The same reason all male animals do – to show that they are the best possible partner for females. Deers rut, koalas shout, peacocks show off, men hop on the Wetherspoon’s app and get a tray of Jägerbombs in. It’s a tale as old as time.

And it’s all based on pubs. Not quite. Another study once mocked up newspapers for men to read. If the papers hinted at greater male abundance, the readers would spend noticeably more on Valentine’s gifts for potential partners than if they read a paper containing fewer men.

This is absurd. Yes, but the future of the species depends on it. Humanity needs you to get the beers in.

Do say: “Buying the first drink is a sign that you are acting on an ancient genetic imperative.”

Don’t say: “And I thought you just wanted to get me drunk.”