Our species' success stems from our awesome technology. From fire to farming, we've been inventing cool stuff since at least 3.3 million years ago. Although this technology provides many benefits, some can also be quite detrimental: It can keep us awake.
Although this might seem like a fairly trivial complaint, lack of quality sleep can be a big problem for humans. And whilst we might blame modern technology for keeping us up (I'm typing this from a laptop that lives on my lap until past midnight), it isn't necessarily a modern problem either.
Fire, in particular, could cause some sleep issues. With its artificial light, noise, and need for attention it might have been a big disturbance for our ancestors. And they were using it for almost 2 million years.
The dark side of fire
The invention of fire is often viewed as a big moment in human evolution. And it certainly was (although it wasn't really one moment, taking almost a million years to fully develop). With fire you can scare off predators, make new tools, cook food, and extend the day artificially. All of this would have made that Homo erectus who did master fire the coolest person around (pun totally intended).
Despite all these benefits, it's strangely absent in the archaeological record of our ancestors. Homo erectus was also the first species of immigrants, leaving their African home and conquering most of the Old World. In such a situation you would think fire would be super useful. All its benefits would be especially important as you spread into a strange new world with a harsher environment than you're used to.
And yet fire is conspicuously absent from all the early out of Africa sites. Despite Western Europe being first being occupied around 1.2 million years ago, we don't see hearths on the continent until closer to 400,000 years ago. That's nearly a million years hominins spent in a strange land without a key part of their toolkit.
Given this suspicious absence, some have speculated that fire might not be as great as it cracked up to be. This would explain why it was "abandoned". After all, it can be hot, dangerous, and take a lot of effort to maintain. All of these downsides to fire have some merit to them. And now researchers have hypothesised there might be another.
What if fire just keeps you awake?
Stay woke
There are many ways to test this new hypothesis. Like just getting a bunch of people to try and sleep next to a fire. Or if your lab health and safety is too strict, just get a flickering light and some fire sound effects.
Of course, carrying out lab based studies hardly reflects the real world our hominin relatives would have been living in. And the Westerners typically involved in such experiments aren't exactly the most normal example of humanity.
So the researchers set out to study hunter-gatherers who routinely live with fire as part of their everyday life. That's not to say that they live like Homo erectus and the first Europeans, rather sleeping with a tape recorder in a lab isn't like that. It's also a fairly unusual situation (even for weird Westerners) which could confuse the results. Knowing you're part of an experiment on might keep you awake, after all. Especially if it's linked to evolution, the evilest of the sciences.
The question they asked was fairly simple. Fire can keep you warm and keep temperature fluctuations to a minimum, which should help you sleep. But it's also bright and noisy, which might keep you awake. So on balance, do the hunter-gatherers examined sleep better with or without a fire?
Well, I shan't keep you in suspense any longer. The answer was "neither". Fire was found to neither help them sleep, or keep them awake. So we're back to square one on understanding why the first migrants to Europe shunned fire.
What else keeps hunter-gatherers awake?
Of course, fire isn't the only way these hunter-gatherers try and control their local environment. The researchers wanted to study other ways the hunter-gatherers stayed warm at night. Did they help any better than fire?
It turns out that yes they did. In particular, the hunter-gatherers built grass huts. These provided decent thermal insulation, keeping the temperature from fluctuating outside of human comfort zones. In fact, given the 28 degrees ambient temperature these huts kept the hunter-gatherers at almost optimal conditions.
This raises another question about those first Europeans. Were they using huts instead of fire? But again, the evidence for early huts is absent. Either they hadn't invented them or just abandoned them altogether, despite the fact that they seem to be a great sleep aid. Maybe Homo erectus was just really good at knapping (again, pun intended).
Either way, there is a curious coincidence here. Terra Amata is an archaeological site near Nice. It's got some evidence of a hearth so, at 400,000 years old, joins the spears as one of the first indicators of fire in Europe. It also contains ( although this evidence is debated) a series of stones placed like the foundation to a hut.
Whoever was living there was sleeping like a boss.
References
Rodríguez-Gómez, G., Mateos, A., Martín-González, J.A., Blasco, R., Rosell, J. and Rodríguez, J., 2014. Discontinuity of human presence at Atapuerca during the early Middle Pleistocene: a matter of ecological competition?. PloS one, 9(7), p.e101938.
Samson, D.R., Crittenden, A.N., Mabulla, I.A. and Mabulla, A.Z., 2017. The evolution of human sleep: Technological and cultural innovation associated with sleep-wake regulation among Hadza hunter-gatherers. Journal of Human Evolution, 113, pp.91-102.
