The other humans, and how they relate to you #2: the Denisovans and Hobbits

2. The Denisovans:

Other than their remains were found in a cave in southern Siberia and contributed to the genes of modern-day Melanesians, there isn't much known about the mysterious Denisovans. We don't even have much in the way of remains--the above tooth, plus a broken finger bone; and that's it. However, the DNA inside the remains was still in very good shape and could be examined by scientists. While the remains were originally thought to come from Neanderthals, analysis showed that the DNA was far too divergent to belong to that species of humans; in fact, the Denisovans show nearly as much divergence in time as exists between modern humans and Neanderthals! That is to say, both of these groups were descended from a population that left Africa around one million years ago and split into two groups. The ancestors of the Denisovans went east, and the ancestors of the Neanderthals went west, and while they may have met in the middle overall there was little interaction between the two groups. The Denisovans were, then, a third species, one that was neither modern human nor Neanderthal, but something unique.

Could Denisovans once have ranged all over Asia, in the fashion that Neanderthals did over Europe and the Middle East? Given the existence of admixture with Melanesians, it's certainly possible. What did they look like? Given that we've only got a finger bone and a tooth, its impossible to say, although presumably they didn't range any further outside the human form than the Neanderthals did. Maybe Google Image Search knows what they looked like--I got this picture when I searched for "Denisova":

Great googly-moogly! No wonder modern humans bred with them!

3. The Hobbits:

Homo floresiensis, aka "Hobbits" are the most exotic of the fossil human species, and incidentally the most recent--some of their remains are no more than 13,000 years old, meaning they lived contemporaneously with modern humans for 11,000 years longer than did the Neanderthals (at minimum).

Physically H.floresiensis is the most divergent of any known human species. For starters, they're tiny: about one meter tall, an example of an evolutionary phenomenon known as "island dwarfing." Basically, when animals are isolated on island environments (and in the case of the Hobbits this was the island of Flores in eastern Indonesia) they tend to get smaller than their ancestors back on the mother continent.

Of the three human species that shared the planet with Homo sapiens, H. floresiensis is the most likely to be considered a "species" in the traditional view of the term. The Hobbits were, for instance, very likely to be reproductively isolated from moderns, both due to their size and the peculiar features of their brain development. Hobbits had brains one-quarter the size of modern brains, and yet they appear to have been as intelligent as any other early human, capable of making stone tools and engaging in cooperative hunting. Apparently their tiny-but-smart nature was accomplished by shrinking certain areas of the brain while leaving or enlarging others. Given the very intricate nature of brain development in modern human fetuses, it's hard to imagine human-hobbit interbreeding having any sort of happy ending, but who knows? It's not as if we have any evidence for or against. As for the Hobbits' DNA, we know nothing about it--DNA could not be extracted from their remains.

Although the most recent Hobbit remains are 13,000 years old, we don't know when the species became extinct. According to modern Flores natives, there were still little hairy folk around when the Portuguese arrived on the island (16th century). A few optimistic folk speculate that H.floresiensis isn't extinct even now, but lurking deep in the Indonesian jungles in the form of the Orang Pendek (Indonesian for "Short Man"), a hairy little humanlike creature from the folklore of Java (think of the Orang Pendek as Bigfoot's "Mini-Me," if you will).

Okay, sapiens--time to meet the rest of the family

In my previous post on Solomon Island blonds, I brought up the unexpected relationship between New Guineans/Solomon Islanders and a fossil group of humans, the Denisovans. The evidence of Denisovans in the family tree of Oceania was the second such proof of modern human-fossil human mixing during prehistoric times, with the first study showing admixture between Neanderthals and pretty much everybody who isn't sub-Saharan African. Since Oceanians are definitely not sub-Saharan Africans, that means they've got both Denisovan AND Neanderthal ancestors, with the bulk of their genes being from a group that left Africa 50-60,000 years or so ago.

So, you might be asking, this is all well and good, but what the hell does it mean, exactly? First off...what's the difference between a fossil and a modern human?

Whew...ye gods, how do I brew this down into a few sentences? "Modern humans"--meaning people who look more or less like the sort of people you see wandering around now--originated in Eastern Africa 200,000 years or so ago. At the time of these earliest "modern humans" there were older populations of humans who'd left Africa a million or so years ago to inhabit Europe, the Middle East, and Asia. Since there was no little or no mixing between Africans and the people in Europe, Asia, etc. over the intervening 800,000+ years, the people on these continents had developed greater physical differences than Africans, Europeans, Asians, etc. possess now. These physical differences were sufficient enough that these regional human variations are usually considered to be not just different races, but different species altogether. Just as there are different species of parrots or dogs (domestic dogs, coyotes, wolves, etc.), two hundred thousand years ago there were several different species of humans.

Between the mid-1980s and last year, the majority of scientists considered these various human species unlikely to have successfully interbred. The modern humans who lived in East Africa finally decided to get off their caveman arses around 50-60,000 years ago and go check out the rest of the planet, and when they did they were so superior to the older human forms that they simply wiped them completely out.

This hypothesis, called "Out of Africa" received a bit of a serious blow in early 2010, however, when it was shown by scientists at the Max Planck Institute in Leipzig, Germany and UC Santa Cruz that modern human DNA could be shown to have Neanderthal ancestry. The older idea of us moderns tromping out of Africa and hunting down the hapless, stupid, and hairy Neanderthals was out. Our ancestors had made love, not war, and the evidence could still be shown in Europeans, Chinese, and Papuans.

The picture of human prehistory got even messier in December 2010, when researchers sequenced the DNA from a fossil finger bone and a tooth. They were able to show that the owners of the finger and tooth were not Neanderthals, as they expected, but a second group of humans that had been isolated from the Neanderthals for 500,000 years or more. Since the relics came from a came in southern Siberia known as Denisova Cave, these people have come to be known as the Denisova Hominids--and their DNA was still apparent among the living people of Oceania.

So, got all that?

Next up, we'll get to actually meet the fossil humans whose neighbourhoods our thoughtless, boorish ancestors blundered into all those years ago.

More on unexpected human phenotypes

The children below are from the Solomon Islands in the South Pacific. They aren't mixed; despite their dark complexions children are very often born with blond hair:

Normally as the children age, though, their hair darkens, turning a dark brown or black. In some cases, such as this woman, it remains a sort of dark reddish-brown:

As far as I know, the genetics of this hasn't been investigated, but this phenomenon is also seen among the Aboriginals of nearby Australia, where blond children and teenagers have been noted, especially among the desert tribes, for a long time.

Incidentally, the people of New Guinea and the Solomon Islands (or at least Bougainville Island, which is close to the Solomon Islands) were recently found to possess some truly exotic ancestry--they still retain genes that appear to be from a newly-discovered prehistoric species of humans called the Denisovans. Since the only known fossil remains of the Denisovans have been found in Siberia, that either suggests the ancestors of the New Guineans/Bougainvilliers took the scenic route when they left Africa (and weren't adverse to getting they freak on with the nearest cavemen), that the Denisovans were much more widespread throughout than just Siberia, or the ancestors of the Islanders absorbed some group that had already bred with the Denisovans.