Success by denaturation

You find yourself on a mountain slope, overlooking a wide green valley. The sun is beating down, but is not all that hot yet; after all, it’s still only mid-morning. You can smell the wet dirt from last night’s rainfall and the air is dense with the noise of insects. In the distance, big herds of wildebeest and zebra are slowly moving across the plain, eagerly feeding off the fresh green grass. A small group of elephants are drinking by the shallow river, two of the smaller calves are playing in the water, spraying muddy water from their trunks into the air. White-backed vultures are circling high above, riding the thermals, looking for carrion. This is Ethiopia. Or rather, it will be – in another 1.7 million years.

“Of course I look smug: I just invented fire!”

Turning east, you can make out a thin pillar of smoke rising from the mountain slope. Moving closer, you realise it’s smoke from a campfire; there are humans around. Soon you can hear them, and carefully looking through some dense shrubs you can see them too: a family group of some 15-20 people, collected around the fire getting ready to have breakfast. They talk and laugh, and the children are running around, chasing each other with small twigs in their hands. It’s all very idyllic and familiar, but these aren’t modern humans. They don’t even belong to our species. What you’re looking at are the evolutionary grandparents of modern humans – this is Homo ergaster.

The campfire in the middle of the clearing is more than just a fire. It’s more than the latest advance in technology. It’s more than a heat source or a means of protection. It’s more than a tool for hardening wooden spearheads and curing animal skin. It’s more fundamental than that. Fire is intrinsically linked with the evolution of humans; it’s the reason we’ve evolved to the modern form, abandoning the ‘chimpanzee-on-two-legs’-look that we’ve favoured for millions of years. Fire made us human. It shaped our evolution and kick-started the rapid increase in brain size.

Fire, fire

What is so special about fire, then? Sure, it’s a convenient tool and useful in many different ways, but claiming it to be the origin of man is a bit preposterous, isn’t it? Well, no, actually, it’s a plain scientific observation. Fire allowed us to do something no other human species – or indeed any other primate – had been able to do: cook our food.

“Didn’t anyone bring any marshmallows? Goddammit!”

Life is a constant struggle. Perhaps not so much today, but 1.7 million years ago it certainly was. And for our great-great-great-uncle Homo habilis – the chimpanzee-on-two-legs I mentioned above – this was particularly true. They were small creatures, only standing 1.3 m (4′ 3″) tall, and they had none of the advanced tool-making to help them like Home ergaster had. They really weren’t much more than bipedal apes.

Homo habilis inhabited the same grassy plains in Africa as Homo ergaster. In fact, they co-inhabited, and would no doubt have met on numerous occasions. But even though they were from the same era of human evolution they couldn’t have been more different. Homo habilis had a very flat nose and a protruding jawbone. Big jaw muscles flanked its face, allowing it to chew on tough roots and nuts. By comparison, Homo ergaster could easily have passed for a modern human if dressed in the right clothes. Sure, they still had pronounced eyebrow arches and a sloping forehead but the body was more or less indistinguishable from ours – tall and muscular and made for running.

“What do you mean ‘chimpanzee-on-two-legs’?”

So what had happened? What had transformed the tiny bipedal chimp to an Olympian athlete? Food. Cooked food. And not even a change in diet; Homo ergaster was eating more or less the same things Homo habilis was: roots, nuts, fruits and the occasional small animal. The difference was that ergaster was cooking its food whilst habilis was eating it raw. And what a difference it made. By heating up the vegetables and meat, fibres were softened and broken up and proteins were denatured. This not only made nutrients more readily available, but it also made the food easier to chew. As a result, it allowed ergaster to devolve those big jaws and jaw muscles, and the additional easy-access nutrients created spare time from foraging; time that could be put to use experimenting with tool-making and developing cultural behaviours. The combination of all this lead to ergaster growing its brains, starting with a 50% increase (compared with habilis) and ending up even bigger some 500,000 years later.

Good food, big brain

That big brain came to good use. The environment was becoming more and more volatile and changeable, with long droughts replaced with lush forests and lakes. The climate was turning unpredictable and only the most adaptive of creatures could keep up.

The increased brain also allowed Homo ergaster to evolve a complex spoken language, which helped them communicate effectively and allowed them to live in bigger social groups, cooperating and helping each other.

Advanced tool-making as a side-effect of increased brain-size.

It also made us the most deadly assassins ever to have walked the earth. No animal, big or small, was safe, and we had soon developed methods and weapons that allowed us to hunt prey so effectively that we could count on a regular diet of meat.

The energy-rich diet also allowed us to grow tall, reaching 1.9 m (almost 6′ 3″). In addition, it would help in maintaining an even bigger and even more expensive brain, starting an evolution of brain size growth that only ended with the Neanderthals reaching the absolute maximum* possible. Anything bigger, and it would be impossible for a human female to give birth to the baby.

And finally, the new cooked diet made it possible for us to venture out of Africa, exploring Asia and Europe. This gave rise to a whole new species of humans which, if longevity is to be the criteria, was the most successful of them all: Homo erectus. Meanwhile, back in Africa, ergaster turned into Homo heidelbergensis, emigrated again to Asia (evolving into Denisovans) and to Europe, turning into Neanderthals. Later still, heidelbergensis became Homo sapiens, emigrated from Africa (again), colonising Europe (again) and Asia (again) and eventually – for the first time ever – reaching the New World. We had finally colonised the whole world**.

Spreading like the plague…

‘Natural’? Don’t talk to me about ‘natural’!

It’s amazing to think that all this, all that is human, is a result of the simple use of fire to cook our food. If we hadn’t discovered fire, we would still be the same bipedal apes that was Homo habilis. Or rather, we’d have gone extinct. Homo habilis didn’t make it. They just weren’t flexible enough, inventive enough or curious enough.

So don’t come and talk to me about ‘natural’ and how good everything natural is. Homo habilis were natural and now they’re dead. By contrast, Homo ergaster used technology to change what they ate and to alter themselves physically – both their bodies and their brains. This was far from natural, but it allowed them to evolve and adapt. And their descendants are still here today, populating the planet – one of which is currently writing this blog post. Being natural is for fossils; embracing technology is the future. And it’s still as true today as it was 1.7 million years ago.

 

* Neanderthals had the biggest brain any human species ever had, with females having an average brain capacity of 1,300 cc and males 1,600 cc. Compare this with our own average brain capacity of 1,100 cc for women and 1,350 cc for men.

** Except Antarctica, which we only started to colonise some hundred years ago.