It’s been around 150 years since the grey squirrel was released onto the farms and country estates of England’s landed gentry.
Considered at the time to be ‘exotic’, the Victorians had little understanding of how this American import would devastate the native red squirrel population. The grey quickly outcompeted its British rival in almost all respects. And, worse still, they carried a pox-virus which was harmless to themselves, but lethal to the red.
The endangered European Red Squirrel
Bigger, stronger, able to store more fat, prolific breeders and the carriers of a deadly disease, the grey squirrel seemed set to drive its weaker cousin to extinction. That is, until the resurgence of an ancient predator.
Around the time that the British aristocracy began releasing grey squirrels onto their estates, their gamekeepers were busying themselves massacring the one wild animal that could keep the squirrel’s population in check: the pine marten. This cat-sized relative of the weasel was hunted to near extinction in order to protect the shooting land and sporting estates of the rich. Now, after decades of persecution, the pine martin is largely restricted to Scotland and the border counties of Northern England.
However, the species was given full legal protection in 1988, and its population has been slowly recovering ever since. And here’s the thing: ecologists have noticed that wherever the pine marten’s population increases, so does the red squirrel’s. Strange, eh? considering the pine marten was once the red squirrel’s chief predator…
So, what’s going on?
The beautiful European Pine Marten
The answer is quite simple: the red squirrel remembers the pine marten. Despite the two species being separated for more than a century, the red squirrel remembers the scent of a pine marten, its hunting technique, their waking hours… the two species evolved together, and information about the pine marten is encoded into the red squirrel’s DNA.
Fortunately for the red, the grey squirrel hasn’t got a clue what a pine marten is, and subsequently often ends up as lunch. And so, even though the pine marten is still a key predator of the red squirrel and will hunt them if able, the damage they do to the grey squirrel population far outweighs these losses, and the red is recovering.
'Long live the pine marten', we say.
This concept of ‘genetic memory’ is also at the heart of a long-running discussion on the development of an iconic stone-age tool: the Acheulean hand axe.
The Acheulean (dating from around 1.7 million - 160,000 years ago) is known as an archaeological industry, that is, a period of time notable for the production of a specific type of artefact – in this case, the hand axe.
Fashioned by our ancestors, Homo erectus, the Acheulean hand axe was big and bifacial (i.e. worked on both sides). Often teardrop or ovate in shape, they are an iconic tool of the Palaeolithic, and instantly recognisable. They are also the most geographically widespread and long-lasting artefact of any period, being in constant production across three continents for roughly 100,000 generations, or 1.5 million years.
An Acheulean Hand Axe, now available in the Timeless Galleries
And here lies the conundrum: why was the Acheulean hand-axe so long-lasting in design (or ‘conservative in character’ as a paleoanthropologist might put it)? Why did the design not change over that massive timespan?
The answer appears to be that the hand axe was a product of culture, rather than technological innovation. In other words, primitive man learned how to make these (quite advanced) stone tools over a very long period of time by a process of continuous imitation– i.e., thoughtless copying.
Of course, the tool’s design and complexity would slowly evolve over the millennia as mistakes in the copying resulted in advantageous modifications (this can be seen in the way hand axes became smaller, thinner, and less elongated over time).
Much like biological evolution by natural selection – the more effective axe designs won through.
This cultural copying of axe-knapping technique explains why the fundamental design lasted for over a hundred thousand generations. There was little, or no, thought involved – just senseless imitation, perhaps aided by basic tuition. Plus, the continuous copying of hand axes for over a million years would also explain why there was a degree of regional variation in their shape. Acheulean hand axes found in England differ slightly to those found in North Africa, as do those found in India. Local errors in copying produced local variations in design.
And so that’s that. Acheulean hand axes were the world’s first meme. A culturally derived copy of a copy, blindly passed on by non-intellectual means.
Or were they?
Back in 1948, the American archaeologist, Hallam L. Movius, drew a line on a map that cut through Ireland and central England. From there it jumped the channel and bisected the Netherlands, Germany, Poland, the Ukraine. It passed through the Caspian states and into India, finally ending somewhere in Bangladesh. Everywhere south of this line, you might find Acheulean hand axes. Everywhere above it, you wouldn’t.
Other archaeologists eventually called it The Movius Line.
The Movius Line and the Eurasian Ice Sheet
Why were Acheulean tools missing north of this line? Perhaps it can be partly explained by the weather – much of northern Europe and Asia were uninhabitable during this period. People did not migrate there. However, this doesn’t explain the lack of Acheulean tools in East/South-East Asia which remained relatively ice-free.
As it turns out, the reason we find no Acheulean hand axes in South-East and East Asia is that the ancient people migrating out of Africa to these places passed through lithological bottlenecks. I.e., they migrated through areas which simply did not have the right type of stone to make axes. And as the production of axes was a cultural thing rather than a cerebral thing, they eventually forgot how to make them.
So why, in 2010, were Acheulean hand axes found in Fengshudao, China, 1500 km north of the Movius Line? How on earth did they get there?
It would have taken many generations of migration to reach Fengshudao. The people that made this journey would have had to pass on the secrets of axe production without actually making any axes for hundreds, perhaps thousands, of years. Or, they would have had to be in continuous contact with people that were making axes over a thousand miles away. Both of these scenarios are highly unlikely.
The answer may be that, much like the red squirrel’s inbuilt ability to detect and avoid the pine martin, axe-making was genetic. Homo Erectus didn’t understand how to make an axe, he was built to make them. It was in his genes, just as it is in a bird’s genes to know how to make a nest or sing a song.
Of course, copying and practice would still play a part (juvenile thrushes will sing softly to themselves until they’ve got it right), but the fundamental design and building of an Acheulean hand axe was probably an innate skill, buried deep in primitive man’s genome.
It has been suggested that high‐quality stone was rare in the eastern part of the range of H. erectus, but forest fires periodically uncovered suitable raw material in river basins. Whenever this happened, so the hypothesis goes, the hominins occupying the area produced bifacial axes. For Homo erectus, thousands of years may elapse, but whenever the rocks show up, the axe-making ability returns.
This would also explain the Acheulean hand axe’s incredible uniformity and longevity. Genetic evolution takes a very long time – millions of years – and, therefore, so did the evolution of the hand axe.
Of course, the genetic transmission hypothesis is just one of many, and the truth is probably a combination of several - but it is arresting to think that buried deep within our own genetic make-up, long switched off and junked, are the coded instructions on how to make an Acheulean hand axe.