The absence of AMELY suggests that a sample is female, but it isn’t definitive. That’s both because it’s impossible to rule out some problem with identifying the protein in samples this old, and in part because some rare males (including at least one Neanderthal) carry deletions that eliminate the gene entirely.
Another key aspect is that some of the 425 amino acid locations differ between hominin species, and even individual members of Paranthropus. Thus, they can potentially serve as a diagnostic of the relationships between and within species and help address some of the confusion about how many species of Paranthropus there were and their relationship with other hominins. While it’s difficult to say too much with only four samples, the researchers found some suggestive evidence.
For example, they tested whether you might see the sort of amino acid variation found among these samples if they all belonged to the same species. This was done by randomly choosing four human genomes and examining whether they had a similar level of variation. They concluded that it was “plausible” that you’d see this level of variation among any four individuals that were chosen at random, but the population of modern humans is likely to be larger than that of Paranthropus, so the test wasn’t definitive.
Among the 425 different amino acids were 16 that had species-specific variations among hominins. Somewhat surprisingly, Paranthropus robustus is the most closely related species to our own genus, Homo, based on a tree built from these variations. Again, however, they conclude that there simply isn’t enough data available to feel confident in this conclusion.
But that should really be an “isn’t enough data yet.” We heard about this paper from regular Ars reader Enrico Cappellini, who happens to be its senior author and faculty at the University of Copenhagen’s Globe Institute. And a quick look over his faculty profile indicates that developing the techniques used here is his major research focus, so hopefully we’ll be able to expand the data available on extinct hominin species with time. The challenge, as noted in the paper, is that the technique destroys a small part of the sample, and these samples are one-of-a-kind pieces of the collective history of all of humanity.
Science, 2025. DOI: 10.1126/science.adt9539 (About DOIs).
