Of our now-extinct cousins, the Neanderthals are by far the best-known. It was believed that they were dim-witted brutes – and, as it happens, our direct ancestors. It turns out that neither was the case. True, the Neanderthals’ societies were probably smaller and simpler than those of Homo sapiens, but they buried their dead, were skilled tool-makers and hunters, and are thought to have used language. Similarly, over the past few decades, they have gone from being regarded as our direct ancestors to a side-branch that we may have helped drive to extinction.

What we have also now discovered – and this came as a real surprise to many scientists – is that humans and Neanderthals actually interbred. Reconstructions of the Neanderthal genome were recently made by a team led by Svante Pääbo, who is based in Germany. The genome was compared with those of living people from various regions. The comparisons suggest that the ancestors of people outside of Africa must have mingled with the Neanderthals some 50,000 years ago; as a consequence, the majority of modern humans are a tiny bit Neanderthal. So, while they disappeared about 30,000 years ago, their DNA did not.

The Neanderthals occupied the western parts of Eurasia until modern humans took over, but when the team which put together their genome turned its attention to the east, it came up with another surprise. Fossils found in the Denisova Cave in Siberia turned out to date from about 50,000 years ago. One finger bone had exceptionally well-preserved DNA, allowing its genome to be reconstructed and compared with those of Neanderthals and various modern humans.

This bone, it turned out, belonged to another group entirely, closer to Neanderthals than modern humans: the Denisovans. Today, there is only one group of people alive who show traces of their DNA – the aboriginal peoples of Australasia, whose ancestors must have interbred with Denisovans living in south-east Asia on their way south.

In short, over the past few hundred thousand years (a mere sliver of time in geological terms), there were perhaps half a dozen kinds of human all alive at the same time, occasionally meeting and very occasionally having cross-species sex.

But there was another, much stranger, human-like species alive as recently as a few thousand years ago – a tiny, mysterious creature whose discovery was one of the most sensational of the last decade. East of the large island of Java is scattered a remote, beautiful, tropical archipelago. Until 2004, it was thought that only modern humans had reached these small Indonesian islands. But in that year, two sensational papers were published in Nature announcing that the remains of a new species had been excavated in Liang Bua Cave on the island of Flores.

This extraordinary little creature, named Homo floresiensis (aka the Hobbit), was only about one metre tall and very small-brained. However, there is evidence that the Hobbits were intelligent: Liang Bua Cave contained evidence of tool-making, butchery of animal carcasses, and fire. What was even more remarkable was the fact that Homo floresiensis survived there until about 17,000 years ago.

So who were these Hobbits, and where did they come from? At first, it was assumed that they were castaways, descendants of Homo erectus who had somehow got to Flores, perhaps by boat. Due to the limited resources available on their new island home, the species then started to shrink (a process known as island dwarfing).

The latest studies of the Hobbit bones, however, have led to the radical idea that these tiny people were in fact descended from something even more primitive than Homo erectus – yet another species, whose ancestors emerged from Africa two million years ago or more, and then evolved in isolation in south-east Asia, finally disappearing only within the last 20 millennia.

So given there were all these forms of “human” over the past million years, what happened to the rest of them to leave us unchallenged? Well, we don’t know when Homo erectus disappeared, unless the Hobbit is its direct descendant. And we have no idea what happened to the Denisovans. But in the case of the Neanderthals, their final demise seems to have been the result of a double whammy: climate change, and the arrival of a competitor – us. We most likely out-competed them for food and other resources, making better tools and being helped through the bad times by our larger and more organised societies.

Whether the arrival of Homo sapiens in Flores was also the final straw that finished off the Hobbit is still unknown; it is possible that a massive volcanic eruption was responsible. But in a final twist to the story, it seems that Africa could have been home to yet another species of human within the last 50,000 years, based on signs of possible ancestral DNA in modern African populations, and fossils found in Nigeria and Congo. Could ancient humans, thought to have been extinct hundreds of thousands of years earlier, have survived in central Africa far longer than anyone suspected? There have been some extraordinary discoveries in the past decade, and we can expect even more in the ones to come.