The three human subspecies known to have hybridised to produce the present human population of the planet, Neanderthals, Homo sapiens and Denisovans, last had a common ancestor more than half a million years ago. Until now it has been assumed that the only branch of her descendants to think symbolically was us, Homo sapiens. In fact, until the development of sequencing techniques sensitive enough to work on ancient DNA, it was thought that the other two species had died out entirely, rather than leaving portions of their genome in European and Melanesian populations respectively. But the discovery, reported last week, of palaeolithic art at four sites in Spain that dates from the time when the peninsula was occupied only by Neanderthals, shows that they worked with symbols of stone and paint.

We have no idea what these markings mean. That is in the nature of symbolism, and indeed of language: the meaning of a sound, or a marking on the wall, is given by the community that uses it; it can’t be read by outsiders. We already know that Neanderthals were anatomically equipped for speech; their use of painted symbols suggests that they could make audible symbols and not just visible ones.

One of the effects of the discovery reported last week has been to push one of the standard tropes of science fiction 40,000 years into our past. That was when Homo sapiens met Homo neanderthalensis, another symbolically intelligent species, and our ancestors realised that they were not alone in the universe. We can deduce that these encounters must have been reasonably peaceable, because Europeans and all other populations outside Africa carry some Neanderthal DNA.

Pushing the emergence of language so far back is exciting enough. But the implications are dizzying. If Neanderthals and Homo sapiens developed the capacity for symbolic thought and language independently, the ground for it must have been very well prepared more than half a million years ago, when the ancestors of the Neanderthals first left Africa. If they did not develop it independently, then those ancestors, Homo erectus, must have had a capacity for symbolic thought far earlier than most scientists would think likely.

Animal studies have shown that almost all of the capacities that we once considered uniquely human are shared with animals. Some birds are capable of choosing and using wooden tools, chimpanzees use stone ones, and even sheep recognise one another as individuals. Many creatures communicate with sounds, as well as with smells and expressions. But only humans have symbolic language, so far as we know. Only humans form concepts and combine them as if they were physical tools before using them to shape the world. Now it seems that to be human in this sense is an older and stranger thing than anyone had earlier dared to dream.