Heredity contributes to about 83 percent of the risk of autism in children with the disorder, a new study suggests.I have my own theory on the cause and/or prevalence of autism. The human brain has undergone relatively rapid expansion since we diverged from our great ape ancestor that also gave rise to the Chimpanzee some 5 million years ago. Evolution isn't exactly a flawless process, as witness our own appendixes and wisdom teeth. Growing a larger brain required a lot of changes, and sometimes the different genes that needed to be changed clashed, and produced problems with the developing brains, leading to autism or other brain dysfunctions.
The estimate, from a re-analysis of a previous study, adds a new wrinkle to the ongoing debate over how much autism is inherited from parents. Essentially, the findings suggest that rare genetic traits combine in parents and explain about eight in 10 cases of the neurodevelopmental disorder in children.
However, study author Sven Sandin cautioned that "our results do not give any information about specific genes or other direct causes. It only informs us that genes are important."
Sandin, an assistant professor of psychiatry at the Icahn School of Medicine at Mount Sinai in New York City, noted that the findings also don't reflect anything about the reported increases in autism rates in recent years. The higher rates must have something to do with increased awareness or environmental factors, "and our study cannot shed any light on this," he said.
I'll offer the possibility of a more controversial factor as well. Many human groups evolved in relative isolation of each other, allowing local adaptions that we call races or even ethnicities, They're not exactly real, but their not exactly fantasy either. They represent means of clusters of population traits, and may not be reflected in individuals from that group. Anywho, certain brain adaptions were selected from in such regional groups, and in some cases, the adaptions of different groups were only partially compatible between far flung groups.
With humans moving around more and breeding across racial groups, such incompatible combinations would be struck more often. Who among us knows where our ancestors were 14,000 years ago, a blink of an eye in evolutionary time?
In the long run, evolution would sort it out, by selecting against the incompatible combinations, and strengthening the species, but in the short term, the result is more heartache from autistic children.