Study reveals numerous comparisons existing between ancient and modern human genomes

When modern humans diverged from neanderthals about 500 kya, ancient DNA (aDNA) from fossil remains continued to give light on how neuropsychiatric problems common in contemporary human populations may have started. In a paper published in Neuropsychopharmacology, Michael Gregory and Karen Berman from the National Institutes of Health combine numerous comparisons between contemporary and prehistoric human genomes to demonstrate how evolutionary remnants influence the risk of developing psychiatric disorders, according to the Indian Express.

It has been well-known for a while that the genomes of Homo sapiens and Neanderthals share a link. In fact, studies conducted in the past ten years have discovered—not very surprisingly—that the genetic material from Neanderthals still present in modern people is not only a relic lying dormant. Fifty thousand years ago, Neanderthals and Anatomically Modern Humans (AMH) interbred, resulting in genetic variations that are still largely functional and still affect the colour of our hair and skin. Depending on the communities studied, the Neanderthal influence on current human DNA can reach 62–64%. In addition, genetic variations from our Neanderthal forebears have aided in our adaptation to temperatures outside of Africa.

Physical traits like the forms of our skulls are frequently indicative of these evolutionary leftovers from our predecessors. The organ that the skull houses is no different. In a recent study, Michael Gregory and his team used MRI images of people who had a significant genetic carryover from Neanderthals to identify changes in how their brains were wired. For example, Gregory et albrain .'s mapping study on the intraparietal sulcus (IPS), a part of the brain involved in processing visual stimuli, hand-eye coordination, and numerical memory, discovered that people with higher Neanderthal genetic content had better functional connectivity with visual processing regions. However, they showed a significant decrease in IPS connection with social cognition-related areas.

Unexpectedly, links have also been discovered between brain illnesses. There is a great deal of overlap between the parts of our brains that we inherited from Neanderthals and the parts that are in charge of illnesses like schizophrenia, supporting the idea that illnesses like schizophrenia only developed after the development of "higher order cognitive capacities." Furthermore, stem cells' development was found to be markedly slowed down in a lab experiment when ancient human genetic variations were introduced. Gregory and colleagues' earlier research had demonstrated that people with "less Neanderthal-derived genetic variation" have a higher risk of developing acute schizophrenia. At the same time, those people who had a higher percentage of genetic material from Neanderthals displayed "less severe psychotic symptoms."

Gregory et al. add to their research by linking Neanderthal introgression to dopamine production, which is created in particular "dopaminergic" regions of the brain and induces the feeling of motivation towards/away from something. The study discovered that dopamine synthesis decreased as Neanderthal admixture increased. The discovery is important since there is a clear connection between increased dopamine production and the likelihood of developing schizophrenia. Since the 1950s, when chlorpromazine, a dopamine suppressor, was able to provide symptomatic relief in patients with schizophrenia, this connection has been widely acknowledged in the medical world. To this day, the dopamine-schizophrenia hypothesis has persisted despite going through several versions.

Gregory and Berman argue that, even though research into ancient DNA is still in its early stages, advances in sequencing, repositories and new potential discoveries of ancient genetic material hold enormous promise for providing us with a glimpse into the evolutionary processes that give rise to serious psychiatric conditions.