Science discovers new ignorance about the past

My recent Times column on new discoveries in the history of our species:

It is somehow appropriate that the 850,000-year-old footprints found on a beach in Norfolk last May, and announced last week, have since been washed away. Why? Because the ephemeral nature of that extraordinary discovery underlines the ever-changing nature of scientific knowledge. Science is not a catalogue of known facts; it is the discovery of new forms of ignorance.

For those who thought they knew the history of the human species, the past few years have been especially humbling. There has been a torrent of surprising discoveries that has washed away an awful lot of what we thought we knew, leaving behind both much more knowledge and many more questions.

I do wish people would teach children this about science: that it is the richest source of new mysteries. To paraphrase George V, bugger Boyle’s Law: tell the kids about how we keep finding things we do not understand. That way they might find silly forms of superstition and mysticism less enticing.

The Happisburgh footprints are hundreds of thousands of years older than any other evidence of “human beings” living outside Africa. They show that some kind of hominid, possibly the species known as Homo antecessor, was capable of living in a very cold place (Britain was then colder than it is now) long before the cold-adapted Neanderthals had even emerged. Who were these “people”? Why were five of them walking across a tidal mudflat? Did they wear clothes and light fires? New mystery.

And this is just the latest new mystery to emerge from human prehistory. A few days ago scientists from the University of Utah announced that they had found that the Khoisan people of southern Africa — the click-speaking foragers and pastoralists who seem to be the most genetically distant people from all the rest of us — have a bunch of genes in them that came from Eurasians via East Africans, who got them about 3,000 years ago. So which European or Arabian people were messing around in East Africa in 1000BC? New mystery.

Among the genes that those Eurasians took to Africa were a few Neanderthal DNA sequences. Until only three years ago it was considered established fact that Neanderthals died out. Now it’s clear that they didn’t entirely do so, because they mated with the modern non-Africans from whom we are all descended, and did so just enough to leave 2 per cent or so of Neanderthal DNA in most of us. Where and when did that mating happen? New mystery.

And since that 2 per cent is a different 2 per cent in each of us, it is now apparent that about 40 per cent of the Neanderthal genome survived inside modern Eurasians. Sequences that shape skin and hair seem well represented, implying that we perhaps needed Neanderthal genes to cope with the cold. But sequences from the Neanderthal X chromosome are largely missing. Does this imply that male hybrids were mostly sterile, as sometimes happens when sufficiently different mammal species can still just produce fertile offspring but of only one sex (in horse-donkey hybrids, for example, female hinnies are occasionally fertile, but male mules never)? New mystery.

None of the Neanderthal versions of the portion of chromosome 7 that includes FOXP2, the gene vital for spoken language, seems to have survived. Was this because our ancestors found this particular version of the genetic machinery inadequate for fluent speech and (as it were) dropped it, by natural selection? If so, how come the Neanderthal version of FOXP2 itself is so similar to ours and so different from the chimpanzee’s, implying that they did at least have some form of language? New mystery.

Then what about the bizarre discovery in the past six years of the genome of a third species of early man, Denisovans, contemporary with Neanderthals and our (African) principal ancestors? A female of this species left her genes in an unusually thick finger bone in a Siberian cave and, we now know, her species contributed a pinch of DNA to Melanesians and Australians. Who were these people? What did they look like? New mystery.

Go back 11 years and try to explain the discovery that a tiny little hominid with distinct anatomy could have lived on the island of Flores in Indonesia for hundreds of thousands of years until only 13,000 years ago. Who were they and how did they get there across a stretch of sea? New mystery.

Then track back into Africa 120,000 years ago, during a warm, damp spell of climate, and try to put your finger on what it was that made at least one group of Africans so darned good at thriving that they soon displaced all others in the whole of Africa and eventually spilled out into the rest of the world, embarking on a headlong and accelerating voyage of technological discovery that brought them farming, cities, space travel and Twitter. What was it about these people that enabled this to happen then? Language, mind or (my favourite theory) the collective wisdom and idea-sharing that comes with widespread exchange? But whatever the explanation, it only poses more questions: why then, why there? New mystery.

And why does everybody descended from these people — black, white or brown — have such a comparatively inbred genome, far more genetically uniform than that of the chimpanzee? If we went through a genetic bottleneck in the past 60,000 years, when our ancestors apparently numbered only a few thousand people (almost certainly alongside a much larger population that left no descendants), what caused it and where were “we” at the time? On the shore of the Red Sea, eating shellfish perhaps? New mystery.

About the only safe conclusion about human prehistory — as revealed in genes, stone tools and bones — is that some gigantic new surprises are in store for us. And that is the beauty of science: the more you find out, the more you realise what you did not know. The story of human prehistory is not special in this regard. You can tell the same tale of expanding new mysteries in cosmology, neuroscience, the history of climate, the workings of the immune system. On the voyage of science we are perpetually sighting great continents of ignorance that we did not even know were there.