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A large international team of anthropologists, evolutionary theorists, biologists, and historians has identified gender and genetic variability via sequencing of enamel proteins from four Paranthropus robustus teeth within the species. In their study, in the journal Science, the group analyzed proteins preserved in the fossilized tooth enamel of ancient hominins.

Paranthropus robustus was a species of australopithecine that lived in parts of South Africa approximately 1 to 3 million years ago, putting them in the Middle Pleistocene. Unfortunately, hominins from this period are not well understood because DNA does not survive well in fossils. Thus, it is not clear if species like P. robustus form their own group. Some experts contend they belong with Australopithecus africanus.

In this new effort, the research team sought to learn more about P. robustus by studying the enamel protein found on the fossilized tooth remains of four individual members of the group, which were recovered from Swartkrans cave in South Africa.

Prior research has shown that such proteins persist much better than DNA, especially in hot, dry climates such as those found in South Africa. The oldest useful DNA goes back only 18,000 years. The four individuals under study were previously dated to approximately 1.8 to 2.2 million years ago, making them some of the earliest-known members of the group to be studied.

The research team found that the fossils represented two males and two females. They also found molecular level differences between the individuals, some of which were sex-based. This find, the researchers note, challenges theories that suggest early hominins can be sexed by size. They also found what they describe as a genetically distinct individual, which suggests that it may have been from another group or demonstrated a high degree of variation in P. robustus.

The analysis hints at a high degree of genetic diversity among P. robustus, suggesting they likely existed as distinct groups. It also suggests that mating among and between the groups was likely common.

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