Modern humans evolved in Africa around 200,000 years ago. As you may have noticed, we've travelled a fair bit since then. Our flag has been planted on all seven continents. As we spread we encountered more varied environments than our African ancestors had to deal with. Cold climates would have been a particular problem, as much of the world became enveloped in an ice age during our spread.
We know that these climactic challenges drove our species to evolve. But how necessary were those adaptations for migration? Perhaps our ancestors could have survived just fine without them, and they're simply a case of fine-tuning. Or maybe the environments were so harsh that we were trapped until evolution caught up.
New research points to the latter.
Adaptations for the cold
As humans spread out of Africa populations began to evolve and adapt to their new environments. High altitude groups began to get better at dealing with the lack of oxygen, whilst those in cold climates had to deal with all that nonsense.
Due to this, modern Europeans are now better at dealing with colder climates than their African counterparts (although have given up some of their heat tolerance to do so). For example, when someone gets cold their metabolism increases to keep them warm. European, Innuits, and other cold-adapted populations are able to increase their metabolism by twice as much as tropical-adapted groups.
It's also worth noting that these adaptations weren't an example of people being perfectly moulded to the environment. Their circumstances changed as time went on - often because of our behaviour. The result is that these regional adaptations are an ongoing process, often prioritising different attributes at different times. There's no superior human developing, just a bunch of groups trying to best deal with whatever weird circumstances they find themselves in for a few thousand years.
For example, when the ice age overtook Europe people there began to get shorter. This reduced their surface area and helped them conserve heat. But as the climate began to improve a few thousand years later this trend slowed down and reversed. And the list goes on.
Plasticity in the face of danger
Of course, evolution isn't the only way humans can respond to changing conditions. Our body can also adapt over the course of our lifetime. Women who wear miniskirts during winter will actually develop slightly different fatty deposits by the end of the season to compensate for the extra skin on show.
Could these flexible, plastic traits be enough to compensate for the cold environments our ancestors found themselves in? Perhaps it was enough to keep them ticking along until evolution could catch up and optimise things.
A review of research on the subject finds that results are mixed. When people are repeatedly exposed to cold environments their metabolic compensation doesn't get any better. In fact, they seem to start doing worse in the cold. In one study, the time subjects could stay in the cold dropped from over 2 hours to under 90 minutes when they were exposed to the cold every day.
On the other hand, people didn't seem to mind the cold as much on the later days; even if they weren't as physically capable of surviving in it. Additionally, the increased metabolism seemed to kick in a bit faster each time; even if the results weren't as impressive in the long run.
Problems before solutions
Based on all this it does look like the cold was a serious obstacle to our ancestors leaving Africa. Or at least, a relativelty serious one. The results are slightly mixed after all. And that's not the only problem with this idea. As the authors of the review note, most of these studies are conducted on a very small scale involving a few dozen people. Women are under-represented in them also.
There's also the fairly big elephant in the room. Clothes. And all that other cool technology we have. No doubt that could also compensate for the cold, meaning we wouldn't need to evolve so much to deal with it. In fact, perhaps the reason we aren't as good at acclimatising to the cold is because our ancestors never had to. They wouldn't stand outside until they were shivering at the optimal rate. They'd just put on a coat.
But then again, this is also a fairly speculative idea; as common-sense as it may sound. In short, this is an area of study that needs a lot more study. But the implications of all this are still cool. Pun definitely intended.
Pun definitely intended.
References
Daanen, H.A. and Van Marken Lichtenbelt, W.D., 2016. Human whole body cold adaptation. Temperature, 3(1), pp.104-118.
