This week's report of the discovery of another "missing link", an ape- like animal that lived in Ethiopia 2.5 million years ago, adds to the realisation that human evolution was a remarkably fitful, accidental and above all, recent development. The more we know, the less simple it seems. Far from its being a single line of descent, with a few evolutionary dead- ends branching off it, it seems that for hundreds of thousands of years an astonishing number of different species and subspecies of ape-like and then human-like animals adapted, migrated and died out. Although it is clear that modern humans came out of Africa, this was not, it seems, a single process of migration, but an endless series of waves of related species overlapping and competing with each other. Supremacy was established all over the globe by the current model in a blink of Time's eye, the past 100,000 years.
And, far from a steady progression from eating berries in trees to building pyramids, it turns out that these species evolved in a series of relatively sudden steps. Walking on two legs was one, the tripling of brain size was another, the development of language a third. In many ways, the big increase in the size of hominid brains is the most puzzling of these changes. Recently, a number of theories based on new evidence have been put forward to try to explain it. The find in Ethiopia suggests that the use of tools to cut meat could have been the key breakthrough, allowing mostly vegetarian apes to enjoy a high-fat diet of meat and bone-marrow.
Earlier this month, however, a contradictory theory was floated, which is that it was the invention of cooking which boosted the calorie intake of human ancestors by allowing them to eat root vegetables. So there you have it. The success of the human species was made possible by a bunch of renegade vegetarian carnivores hell-bent on exploiting technology to kill and carve. Or by a domesticated tribe of Delia Smiths, keeping their drone-like menfolk in check by stuffing them full of carbohydrates in between their occasional, rather desultory, hunter-gathering missions. This has kept the readers of the less serious press entertained with pictures of the young Raquel Welch in a pelt and much speculation about the sexual attractiveness of Neanderthal women.
But an important point is that the theory of evolution is now entirely accepted. The relevance of new discoveries is not that they help to win an argument against the creationists - that was won long ago. Instead they contribute to a widening popular conversation about the origins of humanity, itself part of increasing the public understanding of science, which is one of the causes to which this newspaper has been committed since its advent.
The twin obsessions of popular science - the search for "the missing link" of human evolution and the hunt for intelligent life elsewhere in the universe - are essentially two aspects of the same phenomenon. The defining characteristic of the modern rational sensibility is the realisation of the insignificance of humanity in both space and time. In space, we may not be alone, but we might as well be, despite this month's report of another star with a "solar system" of planets like ours. And humans occupy an insignificant amount of time; recent advances in the understanding of human evolution emphasise just how short-lived and precarious the "success" of Homo sapiens sapiens has been.
Where does that get us? This kind of pure curiosity is never going to give us better non-stick frying-pans, the by-product of applied curiosity in the form of the Apollo space programme. But the more we understand how it was curiosity itself which selected humans for their unique ability to overrun the world, the better equipped we may be to deal with the unstable and dangerous consequences of our "success". The ease with which so many species died out underlines our fragile hold on the world. It is our capacity for thought, language, for making moral choices, for adapting to changing environments, that has made us what we are today. Finding out more about the missing links of evolution will not make people happier or richer, or bring about world peace. But it makes you think.