PHOTO: Dave Kettering/Dubuque Telegraph Herald/WPN

Psychologists have long been baffled by an apparent long-term rise in the incidence of autism, a psychological disorder that disables children and devastates their families. Some attribute the trend to changes in diagnostic practices, others to factors in the prenatal environment. But mounting evidence that genes and hormones play a role has given rise to a new theory that could have distressing implications for engineers and their spouses.

Among the children of engineers, autism and related conditions are found twice as often as in the general population, according to British studies, and are unusually common even in the grandchildren of engineers. Anecdotally, hot spots of autism have been reported in major centers of engineering, including Silicon Valley; Austin, Texas; and Boston’s Route 128 technology ring.

Autism is a developmental impairment affecting the ability to communicate and socialize. It is called a spectrum disorder, because it can appear in greatly varying degrees, often showing up early in life. Symptoms include poor language development, lack of empathy, resistance to changes in routine, repetitive behavior, and obsessive interests. At one end of the spectrum are people who retreat into their own world and become profoundly retarded; at the other are those with “high-functioning autism” who, though they lack some degree of intuition about what others are thinking, can often figure things out through logical analysis, a “human-hacking” process not unlike the efforts of Mr. Spock, the half-human, half-Vulcan character in the TV series “Star Trek.”

The incidence of autism has been rising around the world, in part at least because the disorder is now more commonly diagnosed than before, although some experts have also blamed other factors, notably the use of heavy metals in vaccine preparations and, according to a recent Israeli study, even the advanced age of the father. But perhaps the most intriguing theory is based on an interpretation of autism that sees the condition as merely the extreme of a continuum on which all of us reside. In this view, autism is a difference not in kind of thinking, but in degree.

The theory’s author, Simon Baron-Cohen, a psychologist at the University of Cambridge, in England, points to inborn mental proclivities, which are set to different levels in different people. At one pole lies the systemizer, who attends particularly to those aspects of the world that form regular, repeatable, law-governed patterns. At the other lies the empathizer, who focuses on nonrepeating events that can be understood as the actions of agents—other minds comparable to our own.

The systemizer looks at your tie and notices the fivefold symmetry in the pattern; the empathizer instead sees soup stains that indicate your low regard for personal appearance. Engineers, as you may have noticed, are more likely to wear stained ties than, say, their business executive bosses, let alone the salesmen and politicians of this world. In fact, engineers are probably the largest single group having systemizing casts of mind.

And, if Baron-Cohen is right, today’s male engineer is more likely to leave the house wearing a stained tie than his professional forebears, simply because he is more likely to be married to a woman who is herself of the systemizing persuasion. In Baron-Cohen’s interpretation, the flow of women into the universities has sorted them, as it long has sorted men, according to inborn mental proclivities—greatly increasing the chances that two systemizers will meet and marry. Such “assortative mating,” as he calls it, would have served to concentrate the critical genes, increasing the chance that such a couple will give birth to the most extreme systemizers of all: those with autism.

The theory is new, but the idea that mating patterns may have increased the incidence of autism is not. In Silicon Valley, where systemizers of both sexes abound, the notion has been the subject of nervous jokes for years.