One of the most consistently jarring things about having a small child is how many conversations begin like this:

Another parent – often the expensively-educated New York Times-reading mother of at least one boy –will say, with the air of someone who is imparting a profoundly original thought, “You know, I always thought gender was socially constructed, but gosh, it’s just amazing how different boys and girls really are.” Her inevitable conclusion? It’s all in their intractable little natures.

Here’s my internal monologue at these moments:

Um, really? If your little boy enjoys trucks, as well as hitting other kids over the head with same, you can’t imagine any other reasons besides testosterone? And if your little girl wants to wear pink it’s just got to be those pesky double-X chromosomes. Because your friends and relations, your daycare, your playground, your nanny – and most uncomfortably, you – couldn’t possibly be part of anything so distasteful as “society.”

I’m sure your little girl is never told how pretty she is when she dresses like Ariel the Mermaid. Your little boy has never met anyone who would tell him that Dora is just for girls, or looks away uncomfortably when he pretends to breast-feed a baby doll.

Blaming biology for everything, and using it to help us dodge responsibility for changing social relationships, is all the rage.

The child-rearing advice industry doesn’t help. Just yesterday I got an email from BabyCenter.com – which has an estimated 44.8 million page views per month – telling me “How girls and boys brains are different.” BabyCenter goes on to explain that “Most experts now agree that basic biology is the main reason that boys act so ‘boyish’ and girls act so ‘girlish.’” BabyCenter explains in some detail that socialization plays a role, noting the influence of marketing and TV, but clearly sends the message that there’s a scientific consensus that it’s mostly about Mother Nature.

But that’s not so. Neuroscientist Lise Eliot, author of Pink Brain, Blue Brain: How Small Differences Grow into Troublesome Gaps found, after an exhaustive study of the subject, “surprisingly little solid evidence of sex differences in children’s brains.”

Sure, there are some biological differences between boys and girls, but we make them much bigger than they need to be. Instead of trying to challenge that, we cling to determinist pseudo-science that encourages us to roll our eyes, shrug and embrace the status quo. Let’s stop this nineteenth-century madness.