A Handy Guide to Ancestry and Relationship DNA Tests
Click here to order our latest book, A Handy Guide to Ancestry and Relationship DNA Tests
Humans Were Not Alone
Scientists Use DNA to Discover a New Human-Related Species
In a first, scientists have identified what may be a new species closely related to humans by using only the DNA from an old bone. If this holds up, it opens the way for a new way to study human evolutionary history.
The results of this study suggest that the world of tens of thousands of years ago had more than just two human-like species. And that there may have been many more migrations out of Africa than previously thought.
A More Crowded World
The only member of the genus Homo running around today are humans. But it wasn't always like this.
In the past, many different Homo species roamed the Earth (Homo erectus, Homo heidelbergensis, Homo neanderthalensis, etc.). As time went on, species started dying out until pretty much only humans and Neanderthals were left. And then the Neanderthals went the way of the Dodo leaving only humans.
The findings of a new study done on a 40,000 year old finger bone call this story into question. Scientists looked at the DNA in this bone and found that it didn't match either Neanderthals or humans. This suggests that this bone was from the finger of an unknown member of the genus Homo.
These results point to a world that may have been less human-centric than scientists previously believed. Apparently humans, Neanderthals and this species were all wandering around Siberia at about the same time. In other words, 40,000 years ago, all three species were alive in roughly the same place at the same time. Add to this the "hobbits" of Indonesia and we have four different Homo species on Earth at the same time.
Of course this all assumes that this DNA is indeed from a distinct new species. More work will need to be done to really establish this fact. If these results do hold up, the next step will be to figure out where this new species came from.
Preliminary results suggest that this species split from a common ancestor with humans about a million years ago. This is before humans and Neanderthals split but after humans and Homo erectus split. This also suggests that there may have been more migrations out of Africa than previously believed.
Humans first evolved in Africa. Evidence points to three major migrations that took human ancestors out of Africa. The first was about 2 million years ago when a group of Homo erectus left. The next was about 500,000 years ago when the ancestors of humans and Neanderthals, Homo heidelbergensis, left. The final migration was around 50,000-100,000 years ago when groups of modern humans left Africa.
The new species must have left sometime around one million years ago. In other words, there may have been a previously unknown migration out of Africa between those of Homo erectus and Homo heidelbergensis.
As scientists begin to look at the DNA of more and more ancient bone fragments, they may find even more new species and evidence for more migrations. Combining this DNA work with more traditional paleontology will give scientists an even more complete look at the evolutionary history of the human race.
Out of Africa hypothesis.
Humans may have shared the Earth with more than Neanderthals like this.
Discovering a New Extinct Species
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.
Mitochondria like this one have lots of DNA.
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.
Discussion about sequencing ancient DNA.
This project was supported by the Department of Genetics, Stanford School of Medicine. Its content is solely the responsibility of the authors and does not necessarily represent the official views of Stanford University or the Department of Genetics.