Human evolution: More clues to the story of our past

It’s been a landmark day for learning about our ancestry and human evolution, with the publication of not one but three major studies.

They include new information about some of our most significant fossil finds, and a report on the retrieval of the oldest-ever human genetic data set. Where to start?

In the first paper, in the journal Science Advances, researchers describe taking brain imprints of fossil skulls of the species Australopithecus afarensis (famous for “Lucy” and the “Dikika child’’) that shed new light on the evolution of brain growth and organisation. 

The international team, led by Philipp Gunz and Simon Neubauer from Germany’s Max Planck Institute for Evolutionary Anthropology, scanned the Dikika child using synchrotron microtomography at the European Synchrotron Radiation Facility in Grenoble, France.

The results show that the brain of A. afarensis, which lived more than three million years ago, was organised like that of a chimpanzee but had prolonged brain growth like humans. That means it had a mosaic of ape and human features, a hallmark of evolution.

The study also resolves a longstanding question of whether this species had a prolonged childhood, a period of time unique to humans that allows us to learn and grow.

“As early as three million years ago, children had a long dependence on caregivers,” says senior author Zeray Alemseged, who discovered Dikika in 2000 and now runs the Dikika Research Project in Ethiopia.

“That gave children more time to acquire cognitive and social skills. By understanding that childhood emerged 3.5 million years ago, we are establishing the timing for the advent of this milestone event in human evolution.”

A. afarensis occupies a key position in the hominin family tree, as it is widely accepted to be ancestral to all later hominins, including the human lineage. Lucy and her kind walked upright, had brains that were around 20% larger than those of chimpanzees, and may have used sharp stone tools, Alemseged says.

In the second paper, published in Nature, an international team provides a new suggested age for the skull of a key African hominin found in Zambia nearly a century ago, and in so doing “impacts our understanding of the tempo and mode of modern human origins,” according to lead author Rainer Grün from Australia’s Griffith University.

The Broken Hill (Kabwe 1) skull is one of the best-preserved fossils of the early human species Homo heidelbergensis and was previously thought to be about 500,000 years old – although dating it has been difficult due to its haphazard recovery and the site being completely destroyed by quarrying.

Now radiometric dating carried out by Grün’s team and collaborators, including the Natural History Museum (NHM) in London, puts the skull at a relatively young 274,000 to 324,000 years old.

The findings also suggest, the researchers say, that human evolution in Africa around 300,000 years ago was a much more complex process, with the co-existence of different human lineages.

“Previously, the Broken Hill skull was viewed as part of a gradual and widespread evolutionary sequence in Africa from archaic humans to modern humans,” says NHM’s Chris Stringer. 

“But now it looks like the primitive species Homo naledi survived in southern Africa, H. heidelbergensis was in Central Africa, and early forms of our species existed in regions like Morocco and Ethiopia.”

The third study, also published in Nature, collected and analysed genetic information from an 800,000-year-old fossilised tooth from the hominin Homo antecessor, revealing that this species was closely related to the last common ancestor of Homo sapiens, Neanderthals and Denisovans. 

And this, the authors say, implies that the modern-like facial features seen in this species have deep roots in the ancestry of the genus Homo. 

This has been suggested before, but it has been a difficult issue to resolve because of the fragmentary nature of the fossil record and the failure to recover ancient DNA from Early and Middle Pleistocene hominins in Eurasia.

In the new work, a team led by Frido Welker and Enrico Cappellini from the University of Copenhagen obtained sets of proteins from the dental enamel of molars of H. antecessor from Atapuerca, Spain, and Homo erectus from Dmanisi, Georgia.

Phylogenetic analysis in collaboration with National Research Center on Human Evolution in Burgos, Spain, allowed them to propose that H. antecessor is a closely-related sister lineage to subsequent Middle and Late Pleistocene hominins such as modern humans. 

They suggest that the shape of the Neanderthal cranium represents a derived, rather than primitive, form.

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