Schizophrenia/Autism Gendered? Really?

Benedict Carey, science reporter for The New York Times has an article that lots of largely dissatisfied people are linking to, about a, um, novel hypothesis that autism and schizophrenia might result from gendered expression of a single gene.

Here are the two most commonly quoted paragraphs

Their idea is, in broad outline, straightforward. Dr. Crespi and Dr. Badcock propose that an evolutionary tug of war between genes from the father’s sperm and the mother’s egg can, in effect, tip brain development in one of two ways. A strong bias toward the father pushes a developing brain along the autistic spectrum, toward a fascination with objects, patterns, mechanical systems, at the expense of social development. A bias toward the mother moves the growing brain along what the researchers call the psychotic spectrum, toward hypersensitivity to mood, their own and others’. This, according to the theory, increases a child’s risk of developing schizophrenia later on, as well as mood problems like bipolar disorder and depression.

In short: autism and schizophrenia represent opposite ends of a spectrum that includes most, if not all, psychiatric and developmental brain disorders. The theory has no use for psychiatry’s many separate categories for disorders, and it would give genetic findings an entirely new dimension.

Read all about it here.

I think it's reasonably well-established that selection-based dynamics between male and female copies of genes can determine the development, size, or even behavior of offspring. Carey cites two probable cases in humans, one affecting infant size (when the mother's version of a gene is recessive her pre-birth babies can be much bigger and smaller if her gene is dominant; another candidate might lead to an offspring being higher or lower maintenance.) Thing is that while those effects are determined by the *sex* of the dominant gene they aren't *gendered:* the effects are pretty much the same whether the offspring is male or female.

What Crespi and Badcock are proposing, however, is that the outcomes are gendered. And more to the point, gendered in ways that are specific to contemporary human behavior. I'm really skeptical about that.

Again, leaving aside practical questions like, oh, I don't know, maybe that autism and schizophrenia can both show up in one person, which kind of cocks up a gendered-expression hypothesis, there are others that are... well, they're practical too.

For instance if a well-managed "autism gene" produced more "manly" male offspring, and if "manliness" made male offspring more reproductively successful** then supporting those traits would be in the reproductive interest of *both* the mother and father. So what would be the point of their genes competing? Same for female offspring and well-balanced "schizophrenia" genes.

For instance, going a step further, why assume it's the *male* version of the gene that would produce more "manliness?" Or the mother's copy of the gene that bolstered "femininity?" Again is there any reason to believe that a mother wouldn't be at least as well-off with more "manly" son? Or that a father's daughter would have better reproductive success if she was more "feminine?" I'm not saying those *are* beneficial, just that even if they were it's not clear why one parent would benefit more than the other, or why male fathers would necessarily code for male characteristics. (Remember also, in humans sex is determined by the male's X or Y chromosome, not the females XX chromosomes. Even more reason to doubt why the father's genes, in particular, would discriminate more than the mother's would when it comes to gendered behavior.)

And then there's the problem of determining how dynamics among copies of the same gene, which necessarily have to be on chromosomes that are *shared by both parents,* could affect outcomes expressed by activity on the non-shared male or female chromosomes.

Oh, and finally is it *really* the case that socialization is unnecessary in boys? Really? No use at all in, oh, say, the ability to read the emotional state of a stereotypical adversary in order to determine whether to attack, negotiate, flee, or even recruit and lead? Really? And given that maternal groups forage up to 90% of the calories and construct more than half the infrastructure in the hunter-gatherer groups that were the dominant social organization for most of human evolution is the handwork and attention to objects that's often so exaggerated in people with autism really of no benefit to female offspring?

And finally? Genes that would differentially affect something like the robustness of a child (or, since I think research has been done on those lines too, on peas) of vegetable seeds have had a *very* long time to work themselves out. Something like schizophrenia/autism, though, that would tend to benefit mainly the stereotypically-assumed, *gendered* behavior of recently-evolved humans though? That's a *very* sophisticated development and (since, remember, *both* parents ought to benefit) an extremely subtle one. That doesn't seem like a whole lot of time for what would surely require a whole lot of evolution since humans branched off from common ancestors, or, for that matter, since primates branched off from... whatever we branched off from.

Anyway, all this is by way of saying while I think there's some merit to the idea of looking for behavioral and developmental patterns that are affected by dynamics between male and female copies of genes there's another paragraph in the Times Article that ought to be quoted more often...

“The reality, and I think both of the authors would agree, is that many of the details of their theory are going to be wrong; and it is, at this point, just a theory,” said Dr. Matthew Belmonte, a neuroscientist at Cornell University. “But the idea is plausible. And it gives researchers a great opportunity for hypothesis generation, which I think can shake up the field in good ways.”

In other words, it's an interesting area to try exploring, especially behavior or development that's affected by gene dynamics but provides benefits or harms regardless of the sex of the offspring. But the researchers are probably barking up the wrong tree about their theory that schizophrenia/autism has a gender component... and possibly barking up the wrong *forest* if they think such gendered expressions are common at all.

[** Remember, for evolution to work it's not enough for *you* to have lots of offspring. If *they* don't also have offspring then evolutionarily speaking your genes aren't successful. --fl]