октябрь 2016.

Have humans stopped evolving?

1 ответ

The issue is, we’ve taken control of our environment like no species ever has. We can control our temperature, our food, we can even delay whether we get pregnant or not. We live in the Arctic, the deserts, high altitudes. We manage to cope because we can think our way around things. We can adapt to environments that would normally kill any other species.

All this changes the fundamental process by which we evolve, as we are taking away some of the selective pressures that we would traditionally have. But I believe it hasn’t stopped us evolving. However, it’s at a much slower rate than we ever have before.

We are seeing some signs of change but they’re contested quite a lot, as separating evolutionary change from environmental change is really difficult. Everything after your conception is affected by nature. From the moment you are two or three cells big, the environment has an impact.

For example, we’re taller now than two generations ago. There is tentative evidence that says people in the west of Europe are inheritably getting taller than they were even just a few generations ago. That is supplemented by a massively improved diet, better healthcare and stuff like that. So it’s hard to definitively say it’s an evolutionary change.

Another one – our jaws are getting smaller. If you look at skulls from western Europe from pre-Industrial Revolution to now, we’ve gone from these beautiful occluding teeth, where they fit together perfectly at the front, to a maladaptation where most people have an overbite. It’s partly an environmental thing, where our diet is more processed, but there’s possibly a genetic link, an inheritable thing. We can’t definitively say this is 100% us evolving, but we can’t definitively say that it’s purely environmental.

However, something as fundamental as whether or not we needed glasses would have influenced whether we lived or died a million years ago, or even as recently as 200,000 years ago. If we look at our nearest ancestors, Neanderthals, then going further back to Homo Erectus and Australopithecines about 2.5m years ago, they were preyed upon by eagles and other predatory animals all the time. We know they could only live in certain areas. They couldn’t cope with certain climatic conditions, so even in our recent human history there have been huge selective pressures. Something like short-sightedness would probably have led to our downfall. If you can’t see a predator walking towards you, or you can’t see if that tribal clan is friend or foe, you’ll be dead very quickly. Whereas now, we just stick a pair of glasses on – we are taking some of these selective pressures away from what we would traditionally have.

About two million years ago, a fully-grown human ancestor would have been about 1.3 metres tall - that’s about the height of a seven or eight-year-old child. It’s only when we got to Homo Erectus and their predecessors that we’re getting to the 1.7metre mark. It’s really recently, about 1.5million years ago, that we got to an appreciable size, but before that, we weren’t very much bigger than chimps.

We’ve got this lovely evolutionary history that we can see right across the body in our recent ancestors. The big toe – the hallux – in Australopithecines and the earlier hominids was pushed to the side, as in chimps and gorillas. It was a grasping tool. But we don’t need that, so our big toe migrated forward to the position it’s in now with the other toes, which gives us more stability. It results in the arch of your foot – that’s there because the toe migrated. If you look at any other primate, they’re really flat-footed. But being flat-footed was detrimental for a biped who needed to walk long distances, as our ancestors did. Even something as fundamentally small as the position of your big toe had massive repercussions for the rest of our evolutionary trajectory.

These selective pressures aren’t massive now. We’ve got to the point where we are specialist generalists. We’re not like the panda that can only eat one diet, or the polar bear which can only live in very few climates, or even other primates like aye-ayes with their very strange fingers and eyes. We can live anywhere.

We’ve now got the evolutionary tool kit we need. All the equipment is there. Anything evolutionary we do now will be refining and honing it. So I think the evolution we’re going to see will be on a micro scale, with the gut flora, the symbiotic stuff that we have. We’ll probably change the relationship with things we have within us, the parasites and so on. It’s unlikely that it will be something like growing an extra long index finger to tap your phone with.

Ben Garrod presented BBC4’s Secrets Of Bones