A definitive cause for autism spectrum disorders (ASD) has remained elusive, although the best picture so far seems to be one of a mix of genetic and environmental factors. This suggests that any genes involved with the condition by necessity are being passed on from generation to generation. A new study now suggests that these genes are being positively selected for.
The study, published in PLOS Genetics[open,DOI:10.1371/journal.pgen.1006618][DX], looked at the prevalence of alleles, or gene variants, commonly associated with an increased risk of ASD. The researchers discovered that these variants were found in much larger numbers than would be expected by chance, and they suggest that this may be because they are also linked to other genes implicated in cognitive ability.
The authors write that this positive selection between the genes thought to contribute to autism and those that might promote intelligence may explain why autism is such a prevalent condition, especially when it seems like it would have been selected against during human evolution.
(Score: 2, Insightful) by Anonymous Coward on Tuesday March 07 2017, @02:05PM
The researchers are saying that genes associated with autism were positively selected for. In other words, these genes are somehow beneficial for survival and reproduction, otherwise there would be mostly negative selection pressure. This is in direct contrast to your "reproductive dead end" hypothesis. Apparently whatever positive selection effect these genes have is stronger than the negative selection effects of autism disorders.
Now why would genes that tend to cause or increase chances for autism be beneficial to survival? The theory here goes that these genes have other effects beside the possibility for autism disorders, namely promoting intelligence. It could be the case that autism spectrum disorders are simply a side-effect/cost of higher cognitive function. In other words, the prevalence of autism in individuals could be strongly related to our intelligence as a species.
Also note that autism is a spectrum, not a binary condition. There are many people high on the spectrum, who have difficulties socializing or other issues, but who otherwise live perfectly normal lives and will never have an ASD diagnosis. It only becomes a problem (and is diagnosed as a disorder) when the autism traits are so extreme that they impede an individual's everyday life or functioning in society. I believe right now we are only seeing the tip of the iceberg, the extreme cases, but we are slowly starting to see more of it as we gain understanding of this spectrum.