Human Variability, Evolution and the Autism Spectrum

So much interesting research is going on here in Philadelphia. Here's a study that was just published yesterday suggesting some visible brain differences show up in autistic people as young as six months. I'm collecting a file on human variation and evolution, hoping to write a series of columns that take an evolutionary view of such conditions as autism, ADHD, dyslexia and shyness. Why are we humans so different from one another? Are some of these differences holdovers from earlier eras, when different types of behavior proved advantageous? When people didn't spent their childhoods forced to sit in chairs and absorb lectures? Or are some of these conditions byproducts of the sheer complexity of the human brain?  

Variation drives evolution, and if our environment changed, some of the people who are labelled with various conditions and disorders might thrive better than those deemed "normal." Does human variation help explain why humans have become such a successful species?  

The new study was summarized in a blog post for abcnews. One thing that struck me about this post was the statement that parents  haven't done something wrong to cause autism in their children. Historians of medicine have reminded me that before the vaccine scare, there was something called the "refrigerator mother" hypothesis. Doctors blamed mothers for being too cold to their children. While the vaccine scare is a problem, the refrigerator mother idea caused pain and suffering for families as well. Here's a piece of the story from the abcnews health blogs: 

The study, which tracked MRI images of 92 infants from 6 to 24 months, found that infants who went on to develop autism may have had brain abnormalities visible on MRI at 6 months of age, before the development of clinical symptoms.

The infants studied were already considered at high risk for the condition because their siblings were diagnosed with autism.

Researchers tracked brain changes in infants at 6 months-, 1 year-, and 2 years old. Then, they formally tested for autism using the standard diagnostic test at 2 years old, the typical age when autism is diagnosed.  

Twenty-eight infants whose MRI results showed slower brain connections went on to be diagnosed with an autism spectrum disorder.

Previous studies have looked at brain changes in babies as young as 1 year old, but researchers said the new study is the first to track changes in infants as young as 6 months old.

According to Dr. Nancy Minshew, director of the NICHD Collaborative Program of Excellence in Autism at the University of Pittsburgh, who was not involved in the study, the current findings suggest that a child might have autism long before he or she begins to show outward signs.

“Parents and primary care physician determination of onset of autism or ASD in the second or third year of life is not an accurate assessment of onset,” said Minshew. “This adds to the evidence that autism develops on its own, so to speak, and not because parents did something or did not do something to cause autism.”

Tracking changes could lead to earlier autism screening and intervention, which may lead to improved developmental outcomes, the authors wrote.