In the recent film ‘Rise of the Planet of the Apes’ the chimpanzee Caesar is the subject of a retrovirus experiment which enormously increases his intelligence. In a series of plot twists, other chimpanzees are infected by the virus and the newly-smart troop finds itself in battle with bigoted and vengeful humans. The stage is set for a sequel!

But the real story of how our chimpanzee cousins and ourselves came to acquire such different levels of intelligence is far more complex and even stranger…

It’s five a.m. on the Washington Beltway and I’m squinting into the sunrise. Later it’ll be searingly hot, but right now it feels good with the top down and the wind tugging at my hair. The Miata glides towards the long loop leading to I-95 North and my destination Boston, still eight hours away. I check the mirror, the road’s deserted – no cop cars – so I press on the gas, ease up to seventy and ride the curve.

The northbound interstate comes into view and astonishingly, it’s empty in both directions. That alone is enough to make me cautious so I ease up slightly then suddenly I spot something very wrong up ahead: I shift down fast and floor the brake – the car fishtails before rocking to a standstill.

And here’s what got me spooked: two endless lines of figures stretch out before me on the freeway shoulders, stationary as statues, each line facing the other across the vacant highway. I engage first gear and creep into the slow lane, halting at the start of the line. Staring back from the shoulder I see the figure of myself, a junior me holding hands with the next in line, my own mother. She, in her turn, is holding hands with a younger version of my grandmother, and so it goes on. No-one says anything and no-one moves.

I glance to my left, to the other side of the highway. There at the head of the line I spot a young female chimpanzee. I lock my eyes with her frozen stare and notice how she too is holding hands with an older female chimp (her mother?). I feel like a visiting dignitary, invited to progress between dutiful guards – each static, reserved and as silent as the grave.

But even the strangest sights pall, especially when nothing seems to be happening. Despite the weirdness I still have to reach Boston so I take stock and cautiously get going: still no traffic on I-95, and still no reaction from the two lines of figures.

I move quite slowly and keep half an eye on my deepening chain of ancestors, flicking past just a few feet away. At just 400 yards I suddenly notice that their skin color is darkening. Abruptly they’re looking a lot like they came from the south of Spain and not the northern Europe of my ancestors (in all that follows, I never see another white face).

I need to make up some time here so I gradually accelerate, still keeping an eye on the endless line of people to my right. Just before five miles I get my next big shock – my forebears stop wearing clothes!

Almost immediately I notice that these dark, naked people don’t look quite so – well, normal; they’re far shorter and skinnier for one thing, with faces like miniature hairless gorillas. I sneak a look at the other side of the highway: the line of apes there still look pretty similar to the chimps I saw at the start but then, I’m not much good at telling apes apart.

At fifty miles there’s yet another development: my naked ape ancestors have suddenly become hairy; they would look quite at home in a primate zoo – which I would never, ever visit, by the way! – I think they’re cruel.

Nothing much changes for quite a while until I pass New York – and then at the 300 mile mark, two hours short of my destination, I see an obstacle in the distance blocking the road. Something has happened to the two lines of figures; they’ve finally converged across the highway and joined up.

I bring my car to a halt and walk to the central reservation to take a look at my primeval grandmother. With one hand she’s connected to my maternal line of descent; with the other she’s the ultimate mother of that chimp I saw back in Washington.

I look at her two daughters: two sisters, one who became the mother of all humanity, the other who became mother to our cousins the chimpanzees. Six million years and just a million individuals connect chimpanzee and me: all those mothers and daughters holding hands, down through the years.

I lean forwards and gently kiss my ancient grandmother, then turn my car around and set off home.

What caused one line of descent to become intelligent and the other to become, well, chimps? The answer is different environments. Humans are those apes that expanded out of the Central African jungles into new niches (the savannas) as a result of fluctuating climate change over the last few million years. When an ecological niche keeps rapidly changing, it’s hard for evolution to optimize the necessary bodily changes. Intelligence plus technology can emulate an optimized body-design on a much faster time-frame (a human plus a machine gun is more lethal than a lion). If a basic level of intelligence already exists (and the African apes were always smart) then that intelligence can be bootstrapped.

Our intelligence is not the result of one genetic mutation. Brains are complex things and hundreds of genetic alterations drove our smartness. The smarter savanna apes survived their tough environment and reproduced, the stupider ones perished without leaving descendants; mutations added new possibilities into the mix. It must have been a long and painful process.

It would take more than a ‘Rise of the Planet of the Apes’ retrovirus to ‘hurry things along’ for today’s chimps, who are already perfectly adapted for their own forested environment … and who, by the way, don’t need our ‘help’ except to not-destroy their habitats.

The vivid imagery of two lines of ancestors, from chimps and humans, converging to our common ‘grandmother’ is due to Richard Dawkins. To follow up what the driver saw, follow the links embedded in the article but here’s a brief summary.

  • Cochran and Harpending argued in ‘The 10,000 year Explosion’ that lighter skins evolved in temperate latitudes due to vitamin D deficiencies following the introduction of agriculture some 10,000 years ago.
  • We know when anatomically modern humans started wearing clothes due to the divergent evolution of head and body lice: it was about 180,000 years ago, 20,000 years after the first emergence of homo sapiens, and coincided with an ice-age.
  • The main proto-human species before our own was homo habilis: shorter, skinner and with a more ape-like face.

The chimpanzee fossil record is very sparse – little is currently known about the evolution of that side of the ape family.