What’s more responsible for the development of the human brain and its associated psychological traits: your genetics, or the environmental conditions in which you were raised? Is intelligence mostly an inherited characteristic, or is it acquired in the early stages of life? A new study published in the Proceedings of the National Academy of Sciences attempts to address these questions by comparing chimpanzee and human brains; it’s found that our own brains have evolved to be more responsive to environmental influences than our primate cousins.
The “nature versus nurture” debate continues apace in the scientific community, and at present there is no clear answer, primarily because it is incredibly difficult to compare the effect of inherited genetic characteristics with developed aspects of the brain over time. There are no “control” groups of humans that have had no parental upbringing whatsoever – if there were, we could look at all of their hereditary traits in isolation, later comparing them to children who have had an upbringing.
In order to shed some light on this question, scientists from George Washington University compared 218 human brains and 206 chimpanzee brains in two ways: organization and overall size. This was achieved by using a magnetic resonance imaging (MRI) scanner, which looks at blood flow within the brain.
The human brains were from identical (or fraternal) twins or at least siblings, whereas the chimpanzee brains came from a variety of members within kinships: mothers, their offspring, half-siblings, and so on. This gave the researchers plenty of variability to look into on both sides. Chimpanzees and humans had a common ancestor around 7 million years ago – short in terms of evolutionary time – which makes these intelligent cousins of ours an excellent comparative aid in studies like this.
Image credit: Humans are able to adapt to new information and learn new skills more readily than chimpanzees can. Sergey Nivens/Shutterstock
Both chimpanzees and humans possess brains that are remarkably “plastic,” readily able to adapt to new stimuli and environmental conditions, and learn new tasks with no prior knowledge of them. This high level of plasticity is thought to be strongly influenced by the development of the brain’s sulci – the folds of the brain – which grow and organize themselves long after birth.
Although the overall brain size did not vary much between family members of both species, the sulci of human brains varied far more between closely related family members than the sulci of chimpanzee brains. This suggests that chimpanzee brains are therefore more limited in terms of their ability to learn new skills or adapt to new situations than humans.
“We found that the anatomy of the chimpanzee brain is more strongly controlled by genes than that of human brains, suggesting that the human brain is extensively shaped by its environment no matter its genetics,” said Aida Gómez-Robles, postdoctoral scientist at the GW Center for the Advanced Study of Human Paleobiology and lead author on the paper, in a statement.
It may have been this increase in plasticity in our evolutionary past that allowed our ancestors to propel themselves ahead with a more adaptable intelligence compared to our primate cousins.