Hybridisation and the science of becoming human

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 in reality, it asks a pertinent question where the punchline is “us”.

Rebecca Ackermann, a professor in the Department of Archaeology at UCT and director of UCT’s Human Evolution Research Institute (HERI), has made a series of in-depth studies of hybridisation and how it has served as an essential 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 their structures indicating that the animals were, in fact, hybrids.
 

Much of Ackermann’s research occurred years before hybridisation in human evolution was confirmed through genetics, making it provocative and highly controversial.

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, Ackermann’s research has expanded beyond measuring the skulls of baboons, to the skeletons of other hybrid animals, including gorillas, macaques, wildebeest, canids (such as 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,” says Professor Ackermann. “We now know this is the case for humans, too.”  

Her research goes back nearly two decades, beginning with a study of the bones of baboons that showed certain anomalies in their structures indicating that the animals were, in fact, hybrids.

The benefits of hybridisation

Much of 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. Along with other scientists, she is showing that hybridisation played a more prominent role in the evolution of Homo sapiens than originally 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.

We are who we are thanks to coming together

Ackermann and her colleagues also suggest 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 and cultural evolution. As occurs with genes, cultural contact and exchange would result in the introduction of variation, innovation and novelty (such as new types of tool, building methods, etc).

Ackermann adds, “The idea that one single ancestral group recently became human then killed off or otherwise replaced everyone else on the planet simply isn’t true.
 

Along with other scientists, she is showing that hybridisation played a more prominent role in the evolution of Homo sapiens than originally thought and has provided fuel for the evolution of a more diverse human species.

“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.”