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How different are our brains from our primate ancestors? This is the question researchers in Germany attempted to answer in a new study published in the Journal of Science Advances. The study looked at brain asymmetry in humans and great apes as seen from endocasts, casts of the inner bony brain case that approximate the size and shape of the brain. Brain asymmetry is imperative to cognition and brain function in humans and has been linked to language and the use of tools.

“Looking at chimpanzees, gorillas and orangutans, we wanted to elaborate on brain asymmetry in humans that has been claimed to be unique to humans in pattern and magnitude previously,” study author Dr. Simon Neubauer told us.

Dr. Neubauer is from the Max-Planck-Institute for Evolutionary Anthropology at the Department of Human Evolution in Leipzig, Germany.

“We expected to find the previously described asymmetry pattern in humans but not in apes,” Dr. Neubauer told us, “and a higher magnitude of asymmetry in humans as compared to apes.”

Brain asymmetry is correlated to hemispheric specialization (functional lateralization) in humans that is related to human-specific cognitive and behavioral capabilities like language and handedness.

“Therefore, it is interesting to find out about these features in our closest living relatives, the apes,” Dr. Neubauer told us, “for better interpretation of the evolution of brain asymmetry and lateralization in the hominin lineage.”

Researchers used endocasts because samples of actual brains of apes, specially of gorillas and orang-utans, are barely available for research

“Based on this data, we could investigate the outer surface morphology of the brain,” Dr. Neubauer told us. “For quantification, we used three-dimensional coordinates of nearly thousand measurement points instead of more traditional distance or volumetric measurements. We were therefore able to capture not only the mean asymmetry pattern but also the variation in this asymmetry pattern, a feature that turned out to be important, as well as its magnitude.”

Dr. Neubauer and his team found that humans, chimpanzees, gorillas and orangutans all shared a very similar pattern of asymmetry including a more backwards projecting left occipital lobe, a more forwards projecting right frontal lobe, a more projecting right cerebellar lobe and a more projecting right temporal pole.

“This is the pattern that has been described to be uniquely human previously,” Dr. Neubauer told us. “However, we found that humans were least consistent and showed more variation around this mean pattern which can be interpreted as increased functional and developmental modularization of the human brain. In other words, human uniqueness of brain asymmetry does not lie in its pattern but the increased variation around this pattern. In terms of magnitude, we furthermore found that humans were not more asymmetric than the other species as expected. Rather, chimpanzees were a bit less asymmetric on average than humans, gorillas and orangutans.”

Dr. Neubauer and his team were surprised that chimpanzees, gorillas and orangutans showed the same asymmetry pattern like humans as this pattern was thought to be uniquely human and linked to hemispheric specialization of brain function in humans.

“As it turned out, this is an ancestral pattern that has evolved far earlier and humans seem to have built upon it to establish hemispheric specialization related to typical human behaviors like language or population-wide right-handedness,” Dr. Neubauer told us.

Dr. Neubauer said we have to be careful in interpreting the endocasts of our ancestors.

“With our new knowledge, we cannot say anymore that an endocast of an extinct fossil hominin showing the shared asymmetry pattern is indicative of brain lateralization related to typical human behaviors,” Dr. Neubauer told us. “We should also have another detailed look at brains of great apes, as far as available, to find out more about brain asymmetry in a broader comparative framework.”