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Wednesday, 15 July 2015

Did meat make you smart?

Before relating this week's encounter, I need to slip you some skinny on the human brain. 

Mine weighs about 1.5 kilograms. Yours might be a little more, because I'm guessing you didn't superglue your index finger to your thumb yesterday.

"Be careful," Susan tells me, as I'm dripping liquid UHU onto a plastic doofer I've shaped to fit into a rough-edged hole inside the drum of her washing-machine that's tearing her clothes every time she does a washing. "Superglue can be dangerous."

"Give me some credit," I say. "Do you know how long I've been using tools? Have you any idea how much skill has seeped into these fingers? Can you imagine the depths of knowledge ... Oops."

"What have you done," she says, with that long-suffering drop in intonation I often hear at the end of women's sentences when they talk to me.

I raise my left hand, which looks like I'm doing a shadow-puppet goose.

"Do not," she says. "Move a muscle. I'll google what to do next."

But I reckon time is short. So surreptitiously I start to pull finger and thumb apart, testing the relative breaking strengths of the new superglue bond and my old outer layer of skin. Sensitive to small clues others might miss, my finely-honed engineer's brain tells me the former is weaker, so I exert a greater force.

"'Do NOT try to pull finger and thumb apart,'" Susan reads from her computer

"Aaagh!" I squeal.

"Pillock," she says.

So Carol's theory, which she explains to me in the garden at little Sally's second birthday party, is that the brains of seabirds are evolving so fast they will soon be the dominant species on Earth.

"They've moved inland to live off humans," she says. "So they're getting more protein than ever before. That's what gave human brains a big boost, back in our days on the African Savannah. 

"You remember them?" she adds, unnecessarily.

"And here's the thing," she continues, indicating two yellow-eyed herring gulls perched on the back fence, coveting their neighbour's birthday cake. "When those buggers rule the world, it's going to be Hell. You know why? They're Nazis."

This seems over the top to me. Did gulls annex the Sudetenland? Hardly. Did they invade Poland when I wasn't looking? I don't think so. "They are just birds trying to earn a crust," I tell her.

"No they're not," she says. "They're evil. They'll be goose-stepping around in jackboots any day now. They'll enslave all humans and conduct fiendish experiments on us."

"No they won't," I tell her and I'm pretty sure I'm right. See, here's the thing about young Carol. She is prone to hyperbole for humorous effect. But study the content of her conversation, no matter how far-fetched, and there's usually some interesting truth in it. 

So when I got home I looked this one up. And it turns out there's science behind what she was saying.

Now I'm not telling you seagulls are going to drop bombs on London. Nor that we will have to fight them on the beaches. Far less that there's a little corporal seagull with a black moustache somewhere, writing a manifesto for world domination.

The science is about how humans got big brains. It's called the expensive tissue hypothesis and it goes back to a 1995 scientific paper by Aiello and WheelerFor the full story you'll need to go to our smart sister site, Three Minute Learning. 

The basic idea is that big brains need lots of energy. But humans burn only about the same as other apes of similar body weight. How can that be?

We do it by saving energy on another expensive organ, said Aiello and Wheeler - our guts. Long intestines are needed to digest vegetation. Short ones do meat. Human guts are shorter than those of other apes. So our ancestors' brains were able to grow as a direct result of eating more meat which let them have shorter guts.

This paper was bad news for vegetarians. The carnivores now had a scientific stick to beat us with. "Meat made us smart" crowed the Mail and Sun, contradicting the evidence on every page. 

But here's the thing about science. Like a man on hot coals it never stands still. In 2011 a bunch of Zurich scientists made Swiss cheese of the smart meat story, by punching big holes in it. 

If the expensive tissue hypothesis were true, animals with bigger brains should have smaller intestines, said Ana Navarrete and her colleagues. So they studied the organs of 100 mammal species and found no trace of that correlation. 

But this left a fact without an explanation. Humans and apes of the same weight burn the same amount of energy. But human brains need more energy than ape brains. Where was it coming from?  

Energy efficiency from walking on two legs was part of the answer, said Navarrete. The other is that humans carry more fat than the rest of the apes. Compare lean body weight rather than total and we humans are burning more energy than other apes.

So not only was the expensive tissue hypothesis disproved. There was no need for it in the first place. 

So nice try Carol and bad luck seagulls. But I'm wondering if evolution is all it's cracked up to be.

When did you last see a gorilla superglue its index finger to its thumb?

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