The human family tree has significant gaps. In the past millions of years, a wide variety of species of primitive and pre-humans populated the earth. The Sahelanthropus probably made the start almost seven million years ago: He was presumably the first pre-human to walk on two legs. What happened next is a matter of debate; around two million years ago, however, it was probably particularly confusing, at that time several genera of pre- and early humans existed side by side: Australopithecus, Paranthropus and individual species of Homo. But who was related to whom and in what way?
Anyone who doubts whether they are related to someone today, resorts to DNA analysis if necessary. But in the case of the earliest putative ancestors of mankind, this type of genetic genealogy fails, the DNA is missing. Because genetic material degrades over time. Anthropologists are instead dependent on comparing the shape of fossils, which are usually only fragmentary.
If the sex is clear, this could help to correctly assign fossils
In recent years, new records have occasionally been announced in the analysis of ancient DNA, recently about a million year old mammoth genome from Siberia deciphered. But the oldest human genetic material, that researchers have been able to decode so far is only around 430,000 years old. That goes back to Neanderthals, Denisovans, and Homo sapiens, but nowhere near the time of Australopithecus.
To make matters worse, the pre-humans of the time lived in Africa, and DNA decomposes comparatively quickly in heat and humidity. The oldest human DNA scientists have recovered from fossils found in Africa is only about 18,000 years old.
Against this background, the euphoria that researchers around Palesa Madupe and Enrico Cappellini from the University of Copenhagen are now spreading is understandable. Instead of looking for old DNA, they looked for old proteins that are sometimes more durable than the genetic molecule. In a study on the preprint server Biorxiv that has not yet been peer-reviewed, they report that they have succeeded in Obtaining protein material from hominin tooth enamel that is around two million years old and draw conclusions about the genetic information. The researchers write that they have made a potentially game-changing breakthrough for paleoanthropology. In fact, they would have at least collected the most ancient information about the genetic make-up of pre-humans.
The team sampled four teeth found in sediments off Swartkrans Cave northwest of Johannesburg in South Africa. They are assigned to four individuals of the human species Paranthropus robustus. With the help of a mass spectrometer, the scientists looked for amino acids, i.e. components of proteins, in tooth enamel and were able to identify hundreds of these in protein fragments. On the one hand, they found evidence that there was great genetic diversity among the members of the Paranthropus genus; it is also possible that one of the individuals belonged to a different genetic group than the others.
On the other hand, they were able to identify the biological sex of the former tooth owner. Because in two teeth they found a protein that only occurs in male teeth: the associated amelogenin Y gene can only be found on the male sex chromosome. Two of the four teeth (including one that was previously considered a female tooth because of its comparatively small size) belonged to male individuals. There was no trace of that protein in the other teeth; they therefore belonged with great probability to female individuals.
The exact relationships between the various genera and species of early humans are therefore still unclear, and since the entire genome cannot be made accessible via proteins, it is also questionable how far the gaps in the human family tree can be closed in this way. Cappellini’s team is already suggesting that research be expanded to include other pre-human species. But even a clear gender determination alone would be helpful. Because if bones or teeth of very different sizes appear, the question always arises: Do they come from different species – or from members of the opposite sex? In the pre-human species Australopithecus afarensis, for example, male specimens were on average more than 30 centimeters larger than their female counterparts. In today’s humans, the difference is only about a third as pronounced. If the sex is clear, this could help to correctly assign fossils in cases of doubt.