The shape of the skull and brain is one of the features of the modern human being Homo sapiens sapiens compared to other human species. An international team of scientists, led by the Max Planck Institute for Evolutionary Anthropology (Germany) has carried out a study on human cranial morphology focused on our closest extinct relatives, the Neanderthals , to better understand the biological bases of the endocranial form. of modern humans. According to Amanda Tilot, from the Max Planck Institute for Psycholinguistics and co-author of the work published in Current Biology , they considered “trying to identify possible genes and biological characteristics related to the spherical shape of the brain ” and discovered small variations in the endocranial shape that surely respond to changes in the volume and connectivity of certain brain areas, according to Philipp Gunz, a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology and another of the study’s authors.
The research experts started from the idea that modern humans with European ancestry possess rare fragments of Neanderthal DNA in their genomes as a result of the crossing between the two species. After analyzing the cranial shape, they identified stretches of Neanderthal DNA in a large sample of modern humans, which they combined with magnetic resonance imaging and genetic information from about 4,500 people. With all these data, the scientists were able to detect the differences in endocranial shape between Neanderthal fossils and modern human skulls . This contrast allowed them to evaluate the shape of the head in thousands of brain MRIs of living people.
On the other hand, the sequenced genomes of ancient Neanderthal DNA also allowed them to identify fragments of Neanderthal DNA in modern humans on chromosomes 1 and 18 , related to a less round cranial shape . These fragments contained two genes already linked to brain development: UBR4, involved in the generation of neurons; and PHLPP1, related to the development of myelin isolation – a substance that protects the axons of certain nerve cells and accelerates the transmission of the nerve impulse. “We know from other studies that total disruption of UBR4 or PHLPP1 can have important consequences for brain development,” explains Simon Fisher, geneticist at the Max Planck Institute for Psycholinguistics.
In their work, the experts found that, in carriers of the relevant Neanderthal fragment, the UBR4 gene is slightly reduced in the putamen, the structure located in the center of the brain that, together with the caudate nucleus, forms the striatum, and that it is part of a network of brain structures called the basal ganglia .
In the case of carriers of the Neanderthal fragment PHLPP1, “gene expression is slightly higher in the cerebellum, which will likely have a damping effect on myelination of the cerebellum,” according to Fisher. Both regions of the cerebrum – the putamen and the cerebellum – are, according to scientists, key to movement. “These regions receive direct information from the motor cortex and participate in the preparation, learning and sensorimotor coordination of movements,” emphasizes Gunz, who adds that the basal ganglia also contribute to various cognitive functions in memory, attention, planning, learning skills and the evolution of speech and language. All of these nanderthal variants result in small changes in gene activity and make the brain shape of certain people less spherical. The researchers conclude that the consequences of transporting these rare Neanderthal fragments are subtle and only detectable in a very large sample.
