THE shards of stone pictured, which have an average length of about 30mm, or 1.2 inches, may provide an insight into the evolution of the human psyche. They were discovered at Pinnacle Point, on South Africa's southern coast, by Kyle Brown of the University of Cape Town and Curtis Marean of Arizona State University, and they are estimated to be 71,000 years old. Such shards are known as microliths. They are made by heating a suitable lump of rock in a fire, and then bashing it, in order to flake pieces off its surface. They are believed to have been employed mainly as arrow heads - and were so used in Scandinavia as recently as 9,000 years ago. From about 40,000 years ago microliths are common. Before that date, only one set of examples, from about 60,000 years ago, had been found. This fact has been used for support by those who think the human psyche evolved separately from, and more recently than, the physique of Homo sapiens. Both fossil evidence and DNA analysis using molecular clocks (estimates of historical mutation rates) agree that Homo sapiens is 150,000-200,000 years old. It is only in the past 50,000-60,000 years, however, that it has really taken off. Some ascribe that late take-off to chance. Others think the human mind crossed a threshold at that time, and the flourishing of humanity is the consequence. The battleground for this debate is the handful of artefacts that predate 60,000 years ago - which is also the moment when Homo sapiens left Africa and started the rise that has now established the species on every continent. The discovery of these particular microliths, which Dr Brown and Dr Marean report in this week's Nature, shows that people 71,000 years ago were able to conceive of making them, to act on that conception and to use the result. That suggests they had bows and arrows, a sophisticated form of weapon. This finding thus adds weight to the argument of those who believe that members of Homo sapiens alive at that time were not, psychologically, very different from those alive today. That their culture was simpler was because there were fewer of them, and inventions needed time to accumulate, not because they were less clever. The existence of these ancient microliths may also have a bearing on a related argument, over why human psychology is different from that of other species. One manifestation of that difference, in the view of some, is extreme altruism - extreme in the sense that people will occasionally lay down their own lives for the sake of others. Such self-sacrifice is most often seen in war, and a controversial hypothesis proposed by a few evolutionary biologists is that it did indeed evolve in the context of warfare, at the time when the invention of weapons such as bows and arrows first made it possible for one group of humans to annihilate another. In those circumstances, heroic self-sacrifice to preserve a band of relatives might make evolutionary sense, since an individual's genes could still be passed on collaterally, through surviving members of the band. That impulse, the theory goes, is still felt today, even though comrades-in-arms are not always blood relations. Such thoughts are a heavy burden for a handful of stones to bear, but that is often the fate of fossil signs of human activity. Each discovery, though, does bring the truth a little closer.