The Way Our Brains Evolved Thousands of Years Ago May Have Led to Bipolar Disorder and Schizophrenia

Changes to the human brain as we evolved may have led to the development of bipolar disorder and schizophrenia, according to a study.

Scientists believe that some mental illnesses could be a side effect of how quickly our brains expanded and developed in the relatively recent evolutionary history of the past few hundred thousand years.

Similarly, certain lower back, knee and foot problems are likely caused by our bodies quickly changing to walk upright.

Past studies have linked the risk of developing bipolar disorder and schizophrenia to a gene which helps to transport calcium—which is important for neural activity—in the brain. But scientists don't yet know if the mutation can trigger these neuropsychiatric diseases, the authors of a study published in the American Journal of Human Genetics wrote.

Evolutionary changes in the brain may have led to bipolar disorder and schizophrenia, researchers believe. Getty Images

The researchers looked for what are known as tandem repeats, which affect the expression of the gene that governs how calcium is transported. Tandem repeats are replicated lengths of DNA found either inside or outside of a gene coding sequence, which are believed to turn gene expression on and off and change how our brains work on an individual level.

"In other words, it [the risk of developing mental illness] may be less about the genes you have, and more about how often they are activated and turned on and off," Dr Derek Tracy, of the Royal College of Psychiatrists, who was not involved in the research, explained to Newsweek.

To test their hypothesis that neurological disease could be caused by recent evolutionary changes in the genes that decide how big our brains are, as well as their connectivity and function, the team studied 181 human cell lines and brain tissue samples donated by deceased people to scientific research.

The researchers found that despite efforts to map the human genome, there are still sequences that have been overlooked, Dr. David Kingsley, professor of developmental biology at Stanford University, told Newsweek.

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"The particular DNA repeat arrays we describe in the paper are large, unique to humans, and frequently vary between individuals.

"In addition, we find that different versions of the sequence have different effects when tested in cultured human cells, suggesting different versions may be the causative DNA changes that influence changes in function and disease risk in humans."

The findings are a good example of a previously hidden structural DNA feature that may play an important role not only in human brain evolution but also in human psychiatric disease, he argued.

Tracy told Newsweek: "These variants have a considerable impact on the activation and expression of the gene. It's a finding that appears to have been in plain sight but not actually seen until now."

But the study now needs replicating in a larger and more diverse sample, he argued. And it remains unclear if the association causes mental illness, or if it is a byproduct.