Science | biology
The finding of a recent study is a first step in understanding how these differences influenced our evolutionary success.
They say that differences make us unique, and this is one of those cases. A study conducted by researchers at the Max Planck Institute for Molecular Cell Biology and Genetics (MPI-CBG), in Dresden, in collaboration with the Max Planck Institute for Evolutionary Anthropology in Leipzig, both in Germany, states that the development of the human brain Modern animals have fewer errors at the cellular level than Neanderthals, which could have been an advantage for our evolutionary success. This is the first study to point to a difference in the behavior of brain cells that generate neurons between these two species.
Looking back, since the ancestors of modern humans diverged from Neanderthals and Denisovans (their Asian relatives) 800,000 years ago, nearly 100 of our amino acids (the building blocks of proteins in cells and in tissues) have changed. Six of those changes have occurred in three proteins that are important for the separation and distribution of chromosomes (structures that carry genetic information) during cell division, the process by which an initial cell divides to form two daughter cells.
To analyze the significance of such changes, the scientists inserted the six amino acids characteristic of modern humans into the brains of mice, since these animals are identical to Neanderthals in these six amino acid positions. "What we saw is that three of those modern human amino acids in the KIF18a and KNL1 proteins cause the last of the phases in which the chromosomes prepare for cell division (called metaphase) to last longer, and this results in fewer errors when chromosomes are distributed from neural stem cells to daughter cells, as occurs in modern humans", explains Felipe Mora Bermúdez, lead author of the study.
Then they tried the opposite experiment, introducing Neanderthal amino acids into human brain organoids, structures similar to our organs, but in miniature, that can be grown in the laboratory. “In this case, the metaphase got shorter and we found more errors in chromosome distribution,” he says.
Left side: microscopic image of the chromosomes (in cyan) of a modern human neural stem cell from the neocortex during cell division. Right side: same type of image, but of a cell where three amino acids in the two proteins, KIF18A and KNL1, have been changed from modern human to Neanderthal variants. These 'Neanderthalized' cells show twice as many chromosome separation errors (red arrow). /
This shows that amino acids characteristic of modern humans are responsible for the fewest errors in the distribution of chromosomes observed in our species, compared to Neanderthals. Therefore, it is "highly likely that this improved us as a species, since making fewer chromosomal errors is generally a good thing," says Wieland Huttner, director and research group leader at MPI-CBG, who co-supervised the study.
Intelligence, memory and learning
Still, what biological significance these changes might have had for us is still unclear. Mora-Bermúdez goes a little deeper: «As far as we know, genetic mutations occur randomly and, depending on the effect they have in a certain environment, they can be neutral (they do not generate any effect, which occurs in most cases). ), negative or, rarely, advantageous. If they are advantageous, they are passed on to offspring until all individuals of the same species share them, as happened in this case with modern humans. It's called natural selection and it's part of what allows species to evolve. It is difficult to give definitive testimony as to how these changes at the cellular level may have helped us. We need more studies to confirm its effects on our daily lives and behavior."
The main hypothesis used by scientists is that the changes at the cellular level that have prevented these errors have had consequences at the behavioral level, for example, in terms of improving intelligence, memory or learning, and not so much in prevention. of neurological diseases and disorders, although they do not exclude any possibility. In fact, Mora Bermúdez does not rule out that this knowledge could be used to develop drugs that reduce the chances of cells making mistakes in the context of certain pathologies, although it is "thinking very far into the future". For his part, Huttner points out that "going from better understanding a biological mechanism to turning it into treatments is very complex."
In the next part of the research, which is already underway, they are collaborating with an institute in the Czech Republic specialized in behavioral analysis in mice to confirm whether these changes in the amino acids of modern humans have really had any effect on our behavior . "Despite the fact that the mouse brain is smaller than ours, it also has many similarities and can be very informative, which allows us, in a way, to trace and recreate what evolution did," Mora Bermúdez states.