Two-million-year-old teeth (four sets, in fact) tell new stories in a newly posted preprint paper that strips them of enamel and analyzes what the proteins have to say. This "proteomic" approach, which relied on the more rugged protein molecules instead of fragile DNA, revealed their relationship to the wider family tree of early humans.
Taken from a sediment-filled cave in South Africa, the fossilized teeth once formed the dentition of an ancient hominin, Paranthropus robustus.
This species was diminutive by modern standards, measuring about three and a half feet tall, but it was relatively sturdy in build and weighed about 100 pounds. While P. robustus doesn’t appear to have used stone tools, the species did use bones to dig into termite mounds and its large teeth to chew on nuts and other tough foods.
Four Million Years of Missing Data
Scientists aiming to organize a family tree for early humans have their work cut out for them. Ancient DNA (aDNA) is notoriously fragile and easily destroyed by groundwater and high temperatures. The oldest ever aDNA recovered from Africa was only about 18,000 years old. Which isn't that ancient considering more sophisticated technologies and cultures began to develop about 100,000 years ago.
In 2010, researchers announced that they had sequenced a 400,000-year-old Neanderthal genome from a specimen found in Spain, the oldest example of hominin aDNA to date. But this was a rare feat and only a small part of the tree. Bipedalism first arose some 4 million years ago, and the important human predecessor Homo erectus evolved about 2 million years ago.
Ancient Human Tooth Enamel
For the study, the team extracted proteins from the early humans’ tooth enamel and analyzed them using a mass spectrometer, compiling a large database of information. They zeroed in on one protein sequence in particular that has a male and a female form, which allowed them to sort the specimens into two males and two females. As the paper notes, this technique may help to prevent confusion in the future as researchers distinguish between different species and sexes.
The large team used the wealth of proteomic data to categorize P. robustus as an outgroup to the clade that includes Homo sapiens, Neanderthals and Denisovans. These groups interbred, and modern-day humans still carry genetic material from the latter two species.
The Family Tree
As an effort to make sense of the early human family tree, the paper says it “can be considered a potentially transformative breakthrough for palaeoanthropology.”
Additional studies should focus on extracting a wider selection of proteins from places other than tooth enamel, the researchers say, and scientists ought to investigate other early Pleistocene species such as Australopithecus africanus and H. erectus.
“Nobody really knows yet how useful this will be,” said Beatrice Demarchi, a biomolecular archaeologist at the University of Turin, in an interview with Nature. Another expert, a paleogeneticist, told the journal that for now, analyzing bones is probably more reliable than analyzing proteins when it comes to clarifying family trees.
In 2020, researchers used proteins taken from Homo antecessor tooth enamel to show that while the potential “missing link” species wasn’t a direct antecedent to H. sapiens, it was related as a sister species.