The World Before Us

The World Before Us by Tom Higham

Deep time captivates me. The idea of learning about human prehistory spanning a period of 40,000 years from 70,000 years ago to 35,000 years ago is like contemplating the infinity of space. Written history goes back around 3,500 years. When we first started writing things down, we already had a history that went back ten times that length.

Deep time is deep.

It is also a Dark Age. There is no written record that can let us know what we were doing during this period. We get some clues that push back our scant knowledge as we find megaliths at Gobeckli Tepe erected something like 10,000 years ago. Past that and it is almost total darkness.

But there is candle flicker in the deep past as Tom Higham explains. The candle is the advance in DNA science that have been pioneered over the last twenty years. Because of this science, we have been able to identify a contributor to the human species from a tiny piece of a forefinger and a few other bone fragments. The DNA analysis from those tiny pieces have allowed scientists to identify the Denisovans, whose genetic legacy is found throughout Asia and into deep Melanasia.

I had not realized how set apart Denisovans were from Neanderthals:

While Neanderthals differ from modern humans at an average of 202 base positions along the 16,500 base pairs of the mitochondrial genome, the sample from Denisova cave differed at 385 positions, almost twice as many.

Higham, Tom. The World Before Us: The New Science Behind Our Human Origins (p. 74). Yale University Press. Kindle Edition.

Nonetheless, one of the fragments discovered came from a girl whose parents had included both a Neanderthal and a Denisovan. One would imagine that the odds of this are astronomical.

Recent discoveries are upsetting the linear progression we used to think existed. Higham notes:

At Mandrin, then, it looks as though we have something completely new. Instead of Neanderthals being replaced by modern humans in Europe around 41–43,000 years ago, it seems that moderns entered significantly earlier. They did not persist, however, and were themselves replaced by Neanderthals. It was only around 7–8,000 years later that modern humans once again repopulated the area, this time in greater numbers and at many more sites.

This is the first time we have found an interstratification like this in Europe: first we have Neanderthals, then modern humans, then Neanderthals again, then modern humans. This is obviously extremely significant, but how can we explain what happened at Mandrin? How could humans have entered Neanderthal territory so much earlier than we considered possible? I have two thoughts on this. The first concerns the population of Neanderthals in Europe 50,000 years ago. We have evidence that they were under some degree of stress in terms of their genetic diversity, which was low (I will discuss more of this in Chapter 15). A study of mitochondrial DNA in thirteen Neanderthals showed that they appeared to have gone through a bottleneck and a population contraction.9 We can imagine Neanderthal groups perhaps isolated from one another around 50,000 years ago, and present in lower numbers than before. Perhaps this was the moment when modern humans made this initial incursion. But why did moderns not remain in Europe? Why did Neanderthals replace them later on?

Higham, Tom. The World Before Us: The New Science Behind Our Human Origins (p. 138). Yale University Press. Kindle Edition.

The success of our kind was not a foregone conclusion.

I picked up a lot of cutting edge information, but the problem in my opinion is that Higham spends a lot of time in the technical weeds. He is one of the foremost researchers on the issue of dating artifacts in deep time. He was involved in a lot of the discoveries he discusses. This might be interesting for some people, but as a casual reader, I am less interested in the mechanics of dating. Frankly, I skimmed all of that information to find the juicier parts.

If you like deep discussions of technical problems, then this is your book. If you are interested in nothing but the “gosh-wow!” stuff, then you might not want to invest in this book.