

Mitochondria like this one

have lots of DNA.

The first step in identifying a new species that has gone extinct is to find its fossilized remains. In 2008, scientists found a finger bone in a layer of a cave in Siberia that dated back 48,000-30,000 years ago. In the past, scientists would have needed to find many more bones to establish the relationship of this bone to modern humans. They would use these many bones to piece together a skeleton and compare it to other skeletons. With new DNA technologies, this may no longer necessary. As long as scientists find the bones in the right spot that is.DNA is sturdy but not indestructible. To have a decent shot at being able to read ancient DNA using today's technologies, the bones or teeth need to be have been somewhere dry and cold. This is why scientists haven't been able to get any DNA from all of the more famous African fossils. The DNA is too decayed to read. Luckily the finger bone was in a cold dry place. The scientists ground up a bit of the bone and isolated some of its DNA. They decided to first look at its mitochondrial DNA (mtDNA) because it is so much more plentiful than nuclear DNA. Mitochondrial DNA is a cool relic from the evolutionary past. Instead of just two copies per cell like nuclear DNA, cells can have thousands of copies of mtDNA. This makes it much easier to look at in decayed samples. Even just a few years ago scientists would have had to be content with looking at small bits of this DNA. Nowadays they can look at all of the mtDNA in a cell which is exactly what these researchers did. Once scientists have figured out what the DNA looks like, the next step is to compare it to as many closely related species as possible. If the DNA closely matched any of these, then the bone probably didn't come from a new species. In this case, they compared it to 54 modern humans, 6 Neanderthals, 1 ancient human, 1 bonobo and 1 chimpanzee. But the DNA didn't match any of these. The mtDNA from the discovered finger bone differed from human DNA at around 400 different spots. Human mtDNA differs from Neanderthals at around 200 different spots and from chimpanzees at around 1400 different spots. The mtDNA isolated from the finger bone clearly came from a different species. Of course, mtDNA represents only a tiny fraction of any living thing's total DNA. To really nail down that they have identified a new species, the scientists need to look at the nuclear DNA from this bone sample. Which is what they are doing right now. This is the first time scientists have found a human ancestor using just DNA. If this result holds up, it means that scientists can now figure out human ancestors with only the smallest of bone fragments. As more ancient DNA is studied, scientists will be better able to piece together the more recent evolutionary history of mankind. How many related species lived together at the same time? In the same place? Where did they come from? How did they get there? A whole new door is opening to our human evolutionary past. These results are a first peek. Just wait until the door is thrown wide open.