Modern human brain organization emerged only recently

January 25, 2018, Max Planck Society
Brain shape evolution in Homo sapiens: brain shape of one of the earliest known members of our species, the 300,000 year-old cranium Jebel Irhoud 1 (left). Brain shape, and possibly brain function, evolved gradually. Brain morphology has reached the globularity typical for present day humans suprisingly recently (right). Credit: MPI EVA/ S. Neubauer, Ph. Gunz (License: CC-BY-SA 4.0)

Researchers from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, reveal how and when the typical globular brain shape of modern humans evolved. Their analyses based on changes in endocranial size and shape in Homo sapiens fossils show that brain organization, and possibly brain function, evolved gradually within our species and unexpectedly reached modern conditions only recently.

The evolutionary history of our own species can be traced back to fossils from Jebel Irhoud (Morocco) dated to about 300,000 years ago. Last year's analysis of these fossils by researchers from the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology in Leipzig was highlighted as one of the top science stories of 2017 by a diverse range of print and online media. Together with crania from Florisbad (South Africa, 260,000 years old), and Omo Kibish (Ethiopia) dated to 195,000 years ago, the Jebel Irhoud fossils document an early evolutionary phase of Homo sapiens on the African continent. Their face and teeth look modern, however their elongated braincase appears more archaic as in older human species and in Neandertals. In contrast, it is a globular braincase, which characterizes the skull of present-day modern humans together with small and gracile faces.

In a new paper published in Science Advances, members of the same research team now reveal additional surprising findings about evolution in Homo sapiens. The paleoanthropologists Simon Neubauer, Jean-Jacques Hublin and Philipp Gunz used micro computed tomography scans to create virtual imprints of the internal bony braincase, so called endocasts that approximate brain size and shape. They used state-of-art statistics to analyze endocasts of various fossils and present-day humans.

Evolution of the parietal lobe and the cerebellum

Neubauer and colleagues document a gradual change within Homo sapiens, from an elongated endocranial shape towards a more globular one. Two features of this process stand out: parietal and cerebellar bulging. Parietal brain areas are involved in orientation, attention, perception of stimuli, sensorimotor transformations underlying planning, visuospatial integration, imagery, self-awareness, working and long-term memory, numerical processing, and tool use. The cerebellum is not only associated with motor-related functions like the coordination of movements and balance, but also with spatial processing, working memory, language, social cognition, and affective processing.

The Homo sapiens fossils were found to have increasingly more modern endocranial shapes in accordance with their geological age. Only fossils younger than 35,000 years show the same globular shape as present-day humans, suggesting that modern brain organization evolved some time between 100,000 and 35,000 years ago. Importantly, these shape changes evolved independently of brain size—with endocranial volumes of around 1,400 milliliters, even the oldest Homo sapiens fossils from Jebel Irhoud fell within present-day variation of brain size. "The brain is arguably the most important organ for the abilities that make us human," says Neubauer. But modern human brain shape was not established at the origin of our species together with other key features of craniodental morphology. Neubauer adds: "We already knew that brain shape must have evolved within our own species, but we were surprised to discover just how recent these changes to brain organization were."

Evolutionary changes in early brain development

In present-day humans, the characteristic globular shape of the braincase develops within a few months around the time of birth. Philipp Gunz explains, "The evolution of endocranial shape within Homo sapiens suggests evolutionary changes of – a critical period for neural wiring and cognitive development." The researchers therefore argue that evolutionary changes to early brain development were key to the evolution of human cognition. Jean-Jacques Hublin, co-author and director of the Department of Human Evolution at the Max Planck Institute in Leipzig, says: "The gradual evolution of modern human brain seems to parallel the gradual emergence of behavioral modernity as seen from the archeological record."

The new findings are in agreement with recent genetic studies that show changes in genes related to brain development in our lineage since the population split between Homo sapiens and Neandertals. They add to the accumulating archeological and paleoanthropological evidence demonstrating that Homo sapiens is an evolving species with deep African roots and long-lasting gradual changes in behavioral modernity, , and potentially brain function.

Explore further: Scientists discover the oldest Homo sapiens fossils at Jebel Irhoud, Morocco

More information: Simon Neubauer et al. The evolution of modern human brain shape, Science Advances (2018). DOI: 10.1126/sciadv.aao5961

Jean-Jacques Hublin et al. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens, Nature (2017). DOI: 10.1038/nature22336

Daniel Richter et al. The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age, Nature (2017). DOI: 10.1038/nature22335

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marc verhaegen
5 / 5 (2) Jan 27, 2018
Interesting article, but it confuses skull form & brain organization: it does not show that "modern human brain organization emerged only recently", only that our modern skull form is "recent". Assuming that what is described as "parietal bulging" implies that we have better "orientation, attention, perception of stimuli, sensorimotor transformations underlying planning, visuospatial integration, imagery, self-awareness, working and long-term memory, numerical processing, and tool use" than Neanderthals is a modern example of phrenology. In my opinoin there are much better explanations of why sapiens' brain form differs from that of earlier Homo, google e.g. "Ape and Human Evolution made easy 2018 Verhaegen".
moranity
not rated yet Jan 28, 2018
This would mean that the first wave of Homo sapiens out of Africa (which made up the migrations that populated New Guinni and Australia, around 60 thousand years ago), occurred before this modernisation of brain structure occurred in Africa, so the present similarity in brain structure must be convergent evolution. In fact a lot of migrations occurred before the 35 thousand year mark, Europe had been populated during 50-35 thousand year period, homo sapiens breeding with neaderthals and all that.
So i suppose the first question would be:
Do we all presently show this globular brain structure? If so then it is likely that this change was inevitable in some way as it occurred in exactly the same way in isolated populations.
rrwillsj
1 / 5 (2) Jan 28, 2018
mv, your puzzlement is understandable. I too was concerned that someone was reviving the crankery of Phrenology! Just poorly chosen phrasing for this article.

m, I think it is important to recognize how little reliable data is available. Now, I hold to the position that there was a lot more travel with inter-mixing between population groups. DNA (at the present stage of technology) provides some evidence but not yet conclusive proof for my opinion.

I think there was a lot more travel between paleo peoples than realized so far. Traveling
mainly by dugout or rafts along river systems and coastlines.

The frustration to this hypothesis is that it is very difficult to prove. As most evidence such as campsites boats, remains of humans and game and other signs are easily destroyed and dispersed by flash floods, rising sea levels, grinding ice-sheets, biological decay and other natural phenomena.
marc verhaegen
not rated yet Feb 03, 2018
rrwillsj, I'm not puzzled. The platycephaly seen in archaic skulls (H.erectus, neandertals etc.) is no evidence that they had different brains: their flattened brain-skull was an adaptation to their lifestyle, as seen in other platycephalic mammals, google e.g. "unproven assumptions so-called aquatic ape hypothesis" for an explanation of the loss of platycephaly in H.sapiens & the appearance of a globular skull.

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