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Hybridisation and the science of becoming human

Image: Professor Rebecca Ackermann in Human Evolution Research Institute (HERI) laboratory (credit: Kerryn Warren; Cape Town).
Image: Dr Lauren Schroeder in bone room at State University of New York System (SUNY) Buffalo (credit: Douglas Levere; Buffalo, NY).
Image: Dr Kerryn Warren as Underground Astronaut excavating Homo naledi (credit: Kerryn Warren; Gauteng, Rising Star Cave)

Source: Science Matter, National Research Foundation (NRF) publication (www.nrf.ac.za )

What do you get when you cross a Homo sapiens with a Homo neanderthalensis? This might sound like the beginning of a palaeontology joke, but it asks a pertinent question where the punchline is “us”.

Professor in the Department of Archaeology at the University of Cape Town (UCT) and Director of UCT’s Human Evolution Research Institute (HERI), Professor Rebecca Ackermann, has made a series of in-depth studies of hybridisation and how it has served as a vital creative force in the emergence of modern humans. Her research goes back nearly two decades, beginning with a study of the bones of baboons that showed certain anomalies in the bone structures which indicated that they were, in fact, hybrids.

She documented her findings and used them as an analogue for understanding human evolution. With the help of her PhD students, Dr Lauren Schroeder and Dr Kerryn Warren, and other colleagues, Professor Ackermann’s research has expanded beyond measuring the skulls of baboons, to the skeletons of other hybrid animals including gorillas, macaques, wildebeest, canids (e.g. wolves and dogs), and even mice. This research is showing that small anomalies such as extra or misaligned teeth are common in hybrids, as are large size and significant shape differences relative to non-hybridised species and these same patterns can be seen in fossil human ancestors. “It is well known that hybridisation has played an important role in the evolution of many animals and that this can result in novel organisms, new populations and even new species, many of which turn out to be better adapted to new or changing environments. We now know this is the case for humans, too,” said Professor Ackermann,

The Benefits of Hybridisation

Much of Professor Ackermann’s research occurred years before hybridisation in human evolution was confirmed through genetics, making it provocative and highly controversial. However, in recent years, her work has been proven correct, and along with other scientists, she is showing that hybridisation played a more prominent role in the evolution of Homo sapiens than initially thought and has provided fuel for the evolution of a more diverse human species. For example, to date researchers have shown that the genes of ancient human groups such as Neanderthals and Denisovans persist in living people and have contributed to the diversity of human skin variation and immunity, among other things. This suggests that interbreeding was sometimes beneficial, providing important novelty to the hybrids that helped them adapt in new contexts.

Professor Ackermann also suggests that the patterns of migration and contact that resulted in hybridisation between species would have influenced the development of modern cultures in a kind of parallel genetic/cultural evolution. As occurs with genes, cultural contact and exchange would result in the introduction of variation, innovation and novelty (such as new tool types, building methods, etc.).

“The idea that one single ancestral group recently became human then killed off or otherwise replaced everyone else on the planet isn’t true. Humans arose through a complex process of migration, interaction and exchange over hundreds of thousands of years or more. Our ancestors have never been easily parcelled into discrete groups, then or now, an important lesson in today’s divisive times. Rather, our lineage is best represented by a braided stream, with input from many different groups creating the flourishing and adaptable humans of today in all our glorious diversity. Had hybridisation not occurred, it is unlikely that we would have been as successful as a global species,” she adds.