Some of the same genetic changes that make the human brain unique have also made humans more neurodiverso. A new study suggests that autism may be at the origin of what has made humans solely intelligent.
The investigation, in the September edition of Molecular Biology and Evolutionfound that the genes responsible for the human intellect increase the likelihood of presenting autistic or schizophrenic traits.
As it is rare to find the behavioral traits of autism or schizophrenia in nonhuman primates, the investigation team suspected that there could be a genetic reason for these conditions to seem to be unique to humans.
As detailed to, the team compared RNA of more than one million cells in three brain regions of six mammalian species: mice, saguis, rhesus monkeys, gorillas, chimpanzees and humans.
The team found that, in general, the most common types of brain cells remained relatively unchanged even among species.
However, there was a great exception: the most abundant type of neocortical neurons – IntraThelencephalic excitatory neurons of the 2/3 layer — changed much faster in humans than in other primates over evolutionary time.
The same pattern has been confirmed in multiple databases and using cerebral organoids made from chimpanzee and human cells.
A neocortical part of the brain is involved in higher order, including Cognition, reasoning and language. The rapid transformation of specialized neurons in this region includes changes in genes associated with autism and schizophrenia.
It is still unclear why these genes have helped our human ancestors survive, but since some of the genes have been associated with a delay in brain development, scientists suspect that they changes may have helped to increase our ability to language and complex thinking.
That is, even if these characteristics have clear advantages, also increase the probability of certain neurodes -development conditions.
“Our conclusions provide the stronger evidence until the date supporting the longtime hypothesis that the natural selection of specific characteristics of humans increased the probability of certain disturbances”The team wrote in the article.
“The exceptionally high prevalence of autism in humans can be a direct result of natural selection to less expression of a set of genes that has given an adaptive advantage to our ancestors, while making an abundant class of neurons more sensitive to disturbance,” he added.
As Science Alert says, if your suspicions are correct, this means that the humans would not exist as they are without the existence of autism.
