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Published: 14 June 2024

Scientists hope to gain insights into the evolution of the human brain

The evolution of the human brain is one of the unsolved mysteries of neuroscience. Since fossils cannot provide information in this area, researchers attempt to reconstruct the brain of common ancestors by studying and comparing the brains of humans and non-human primates. Previously, such studies involved experiments on living animals, such as rhesus monkeys. Now, scientists at the Max Planck Institute (MPI) have published a detailed atlas of the brain of our closest living relatives — without killing any animals specifically for this purpose (1).

Previously, in addition to data from other more distantly related primates, only older images of chimpanzee brains were available, but these showed a limited resolution. Newer images using improved technology were not possible because animal testing on chimpanzees is globally condemned, although unfortunately still legally permitted in some countries, including Germany, in exceptional cases. The brain underlying the atlas therefore comes from a 47-year-old chimpanzee who was euthanized due to an untreatable illness (2). This demonstrates that insightful findings can be obtained without killing an animal for research purposes.

The atlas was created using high-resolution magnetic resonance imaging, with the chimpanzee brain scanned for several days. In unprecedented detail, the brain model that was reconstructed from the images shows how different brain areas of the chimpanzee are interconnected. The comparison of the  chimpanzee brain with the human brain aims to draw conclusions about common ancestors who lived approximately 7 million years ago. This investigation seeks to understand how complex brain functions such as language may have evolved.

The scientists announced their intention to not only compare the brains of humans and non-human primates but also to compare the brains of primates who have had different experiences and acquired different abilities. For example, it is imaginable to compare the brain of animals who have learned to use tools with that of their counterparts who do not use tools. This could yield insights into how brain connections change through individual experiences. For this research angle as well, only the brains of deceased animals will be used. The atlas of the chimpanzee brain is publicly available and can therefore be used by other scientists (3).

An atlas of the human brain has also been created using high-resolution imaging techniques (4). Unlike research on non-human primate brains, such human data allows for a better understanding of the human brain and its diseases, which is not feasible with non-human primate brain research due to differences in brain structure and function (5). However, if studies on animal brains are still to be conducted, using deceased animals provides a more ethically acceptable way to obtain the desired information. It is hoped that in the future, other species, whose use in animal experimentation is less regulated compared to great apes, will also be spared from use in brain research.