A big part of the importance of Prime Minister’s Questions is that it allows a leader to show their side that they’re a winner. Rather than judging it as a debating contest, think of it as some kind of primate display, with two alpha males parading and beating their chests while grunting tribe members behind them hoot, holler and occasionally pick fleas off each other: PMQs Of The Apes.

The dominant tribe in this particular jungle has for years been the Conservatives, but a series of defeats and internal splits has left them weakened and demoralised. Opposite them are Labour, who despite their motto of “no complacency” allow themselves half an hour of public smugness each week.

The two leaders grunted, yelled and showed their bottoms to each other

On Wednesday this manifested itself even before the session had begun. Rumours were swirling that Labour had a third MP defection up its sleeve, someone dissatisfied with the direction of the Conservative Party in recent months and years. This is a group that, let’s face it, includes almost every Tory. Here was Theresa May, who had voted with Labour only two days earlier over excluding MPs accused of wrongdoing. She took her usual seat. Here was Penny Mordaunt, an unlikely defector, but barely less improbable than Natalie Elphicke. She too made her way to her own front bench.

By now Labour MPs were greeting each Conservative arrival with a slowly building noise. “OooooooooOOOOOOOOOOOOH…” they would go, as they walked in, and then “Ahhhhhhh…” as they headed for the government side. They did it to Andrew Selous, and then to Robert Courts, who flushed bright pink. It was bullying and unfair, but also very funny.

The session that followed stuck to the usual pattern, where the two leaders grunted, yelled and showed their bottoms to each other (pretty much) without really engaging. Keir Starmer noted that Rishi Sunak had clocked up “his seventh relaunch in 18 months” and that it was built around Esther McVey’s “vital crackdown on the gravest of threats — colourful lanyards”. Sunak replied that Angela Rayner had voted against renewing Trident. It might have been more enlightening if they’d hurled faeces.

The Labour leader wanted to know details about the prisoners being released early from prisons because there’s no room. The prime minister demanded to know why Labour wouldn’t commit to increasing defence spending. Starmer had a joke about Sunak being a “tech bro who cannot work a debit card,” but he mangled it, prompting a huge schoolboy “Oooooh!” from the bench opposite.

The prime minister seized his moment, saying the Labour leader had “just showed spectacularly why he is just not fit to lead this country into the future”. This seemed a bit of an extrapolation from stumbling over the word “bro”, but it turned out that Starmer’s crime was to have mocked Sunak. “We led the world when it came to the industrial revolution,” the prime minister explained, “but if he was around he would have probably called James Watt the steam bro.”

Even Tories looked a little baffled by that one. Was Sunak, who once purchased a self-heating coffee mug, claiming this made him the reincarnation of the inventor of the steam engine? Is he, like some other owners of iPhones, under the impression that he designed the thing himself?

Does anyone have Jane Goodall’s number?

Starmer did have one card up his sleeve, a report into Lewes prison which suggested that at least one high-risk prisoner had been released early. “Rather than confiscating lanyards like some jumped-up milk monitor, he should stop issuing Get Out Of Jail Free cards to prisoners who are considered to be a risk to children,” he finished.

With the main display over, we heard from a northern tribe of separatist primates, although it may be risky to include them in the joke. SNP leader Stephen Flynn was outraged — OUTRAGED! — about part of Sunak’s Monday speech. “He actively compared North Korea, Iran and Russia with those people in Scotland who believe in independence,” he fumed. “He proactively compared almost half the Scottish population to a war criminal like Vladimir Putin!” Those of us who’d been at the speech checked our notes. This was the kind of thing we would have remembered, had it actually happened.

“That is not what I said,” Sunak replied, in a rare clear and accurate answer. “But I will say that his party is indeed a threat to the integrity of the United Kingdom. I hate to remind him that that is literally its entire purpose.”

Had Flynn joined the SNP without grasping its Big Idea? Of course not. But he also knows his supporters are never so happy as when they can complain that someone is being rude about them. And the point of PMQs is to keep your own side happy. It’s a fascinating ritual. We really need a primatologist to come and have a look. Does anyone have Jane Goodall’s number?