Published on:

Genes generate new mysteries about prehistory

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

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.

By Matt Ridley | Tagged:  rational-optimist  the-times