How far back in time could you go to adopt a baby? That’s the question that comes from Eric today. He’s curious as to how far our modern brain stretches back. Remember, if you’re curious about something you can get in touch through the website.
I understand that Homo sapiens have been anatomically the same as we are today for about 180,000 years. I also understand that the first time any Homo sapiens ventured outside of Africa was about 60,000 years ago. My question is, how far back in time could we go and bring a newborn from that time and raise them in present day and they could be mentally and intellectually the same as we are now?
This question hints at an interesting debate in human evolution that has been going on for some time. Are we the sum of our parts?
As Eric correctly points out, the human species is around 200,000 years old. 195,000 years if you want to be precise. Since then our species hasn’t really changed in any substantial way, beyond minor regional adaptations. In particular, the brain appears to have remained the same. It hasn’t changed in size or shape for those 195,000 years.
Thus, some argued that since we had a modern brain all that time, we must have been as smart as modern people for that long. There’s no notable physical changes that would point to a change in intelligence. As such, Eric could go looking for his adopted child at any point Homo sapiens existed and get a perfectly smart baby.
A super modern brain
However, some contend that there’s more to the human brain than just its size and shape. Neuronal structure, development, organisation, etc. are all important in making a modern brain as well. And we can’t really tell how long they’ve been in the modern structure. Fossil evidence just doesn’t have that high a resolution.
So they speculate that the modern brain may have emerged later than the 195,000 year mark. In particular, they narrow it down to around 50,000 years. This is when the bulk of the out of Africa movement happened. With it a whole new suite of technologies began to appear too. All of this dramatic change, they claim, indicates that something critical happened in our brain. Some sort of mutation shifted our brain structure, making it possible for us to start doing all this cool stuff.
Thus if Eric was to go looking for a foster kid >50,000 years ago it wouldn’t turn out like a modern human. Even though externally they might look the part.
At least, Eric would have trouble if you believe their interpretation. And whilst it was once fairly popular it has fallen out of favour in recent years. This is because all of the evidence that there was this “cognitive revolution” that might indicate a mutation has fallen apart.
One of the crucial pieces of evidence was so-called “behavioural modernity”. This was the suite of traits only seen after humans left Africa, indicating that something may have happened around this time in our brain. Except it turns out that there’s evidence of behavioural modernity gradually evolving along with our species. Things like fancy tools, fishing, art, and more are all seen before the modern brain is supposed to have evolved.
This gradual change is more consistent with cultural evolution than some sort of sudden mutation. As such, most now accept that the underlying brain has been essentially modern the whole time. And so Eric could pick his baby from any point in modern human pre-history and it would be “normal”.
His biological parents might just be a bit behind the times.
d’Errico, F., Henshilwood, C., Lawson, G., Vanhaeren, M., Tillier, A.M., Soressi, M., Bresson, F., Maureille, B., Nowell, A., Lakarra, J. and Backwell, L., 2003. Archaeological evidence for the emergence of language, symbolism, and music–an alternative multidisciplinary perspective. Journal of World Prehistory, 17(1), pp.1-70.
Henshilwood, C.S., D’errico, F., Marean, C.W., Milo, R.G. and Yates, R., 2001. An early bone tool industry from the Middle Stone Age at Blombos Cave, South Africa: implications for the origins of modern human behaviour, symbolism and language. Journal of Human Evolution, 41(6), pp.631-678.
Henshilwood, C.S. and Marean, C.W., 2003. The origin of modern human behavior. Current anthropology, 44(5), pp.627-651.