X-Woman

In March 2010, a pinky bone from  a young hominin - a member of the group of animals that includes humans, chimpanzees and bonobos (sometimes known as pygmy chimpanzees) - was discovered in Denisova Cave in Alta Krai in southern Siberia.

Carbon dating of artifacts found in the cave, including a bracelet, show that the owner of the pinky bone, who became known as X-woman, probably lived between about 30,000 and 50,000 years ago.

X-woman was probably between 5 and 7 years old when it died.

DNA from the X-woman's mitochondria (structures in cells that are involved with energy, respiration and growth) was compared to the mitochondrial DNA (mtDNA) of 54 modern humans from Russia, the mtDNA of six Neanderthals, and the mtDNA of one chimpanzee and one bonobo.

(The name X-woman comes from the fact that mitochondrial DNA passes only through the female line; we don't know the actual sex of X-woman.)

X-woman's mtDNA was found to be twice as different from that of modern humans as the mtDNA of Neanderthals is from us.

Modern humans, Neanderthals and the species to which X-woman belonged had a common ancestor that lived about one million years ago.

Scientists think that modern humans migrated from Africa about one million years ago - after Homo erectus, an ancestor of modern humans, left Africa and before the ancestors of Neanderthals migrated from Africa.

X-woman's species, Neanderthals and modern humans may have interacted with one another and may even have interbred.

In fact, X-woman may have been a hybrid - with a father who was a modern human or a Neanderthal.

X-woman's mitochondrial DNA tells us nothing about its male ancestry.

Researchers believe that X-woman's species probably hunted wooly rhinos and wooly mammoths and wore heavy clothing to keep warm.

The discovery of X-woman shows that at least four different species of human beings - Homo sapiens (modern humans), Homo neanderthalensis (Neanderthals), Homo floresiensis, and X-woman - have lived in Europe and Asia.

This is the first time that DNA sequencing - rather than the structure of fossils - has been used to describe a hominid. (Hominids include humans, chimpanzees, bonobos, orangutans and gorillas.)