The fact that it takes quite some effort to acquire a driver’s license and yet there’s no test required to become a parent has long amazed me. “These things should come with a manual,” I’ve heard several friends moan as they struggle to give their newborn a bath or to figure out how to put a diaper on their baby when the front and back look identical.

When I had my third child, I thought I was finally past that point. I approached the birth itself with well earned trepidation. But as for feeling ready to handle the nitty-gritty of feeding, sleeping, bathing, and dressing my newborn, as well as handling the tantrums and potty training to come, I felt confident that I had seen it all. After my two boys, I was prepared to handle whatever came my way.

But what came my way was a girl.

While the first year or two of feeding and sleeping was familiar enough, I am now desperate for the fantasy manual that can explain to me the power of Barbie, the importance of nail polish, and exactly how it is possible to wear only one color, day after day: pink. I am sure that parents who have two girls or even one, and then a boy, feel the same sort of disorientation.

I have to smile when I think about the feminists in the 1960s and 1970s who valiantly tried to prove that baby boys and baby girls are born identical, only to be ruined by the influence of sexist parents and our sexist society.

It’s not that I haven’t read the studies that show just how differently people treat babies when they think they are playing with a girl or boy. Or the ample studies backing the idea that social construction – not biology – plays the more significant role in creating sexual differences.

But if you speak to parents, the real scientists in the trenches, the overwhelming anecdotal evidence suggests that in the case of sexual differences, nature is more powerful than nurture.

“I don’t care what any study shows,” insisted a friend of mine. “My household serves as evidence beyond any reasonable doubt that the biological difference between boys and girls might just be bigger than that found between humans and chimpanzees.”

Patricia Hausman, a behavioral scientist specializing in the nature and origins of human sex differences, agrees. In an article on the Independent Women’s Forum’s Web site she is quoted as saying that “many argue that changes in the social environment could eliminate sex differences in interests. To me, this perspective mistakenly assumes that the ‘social environment’ is something that Big People force on Little People. I think it is often the other way around.”

She continues: “The Little People send signals to the Big People about what they do and do not like, and the Big People respond accordingly. Parents who buy more dolls for a daughter are probably not forcing them on her. More likely, they are reacting to observations that she did not find a toy truck particularly captivating, but lavished attention on her first doll.”

From my own experience, I resoundingly agree. While it took my boys a few days to get the hang of toilet training, it took Kira about an hour. She took one look at those Barbie underpants and never wore another diaper again. The only problem was that I had also bought packs of princess underpants that included Sleeping Beauty, Cinderella, and Snow White.

These days, it can take Kira up to 10 minutes to choose her underpants. At first, this stereotypical exertion of feminine willpower was so cute I wanted to die. Now, as Kira holds Cinderella in one hand and Barbie in the other, I just want to die.

“I’m not exactly sure why people are so uncomfortable with the notion that boys and girls are biologically different,” said a friend of mine. “To me, and I have one of each, it’s easy to accept that notion and then recognize that since we can’t change the biology, we have a greater responsibility to change our parenting styles and societal influences.”

But there is a big difference between trying to raise sensitive boys and assertive girls. Educators and psychologists have begun to sound warning bells about the dangers of educating our boys and girls as if they were identical. They point to the dangers associated with resocializing little boys to be more like girls. “Boyness” is under attack, according to these experts, who say that the normal assertive, rough-and-tumble play of boys is increasingly viewed as a pathology that must be treated and eliminated.

I couldn’t help but think about this last week, when I took my gang to the Bronx Zoo. For more than half an hour, we sat, fascinated, watching six gorillas in the Congo Forest. There were two adult females, a 1-year-old female, and three young males, ages 2, 3, and 4. My two boys laughed hysterically as the young male gorillas wrestled each other, rolled in the hay, and actively jumped around. My 6-year-old turned to me and astutely commented, “Look, it’s just like me and Josh.”

The young female sat quietly, and even occasionally placed her hands over her ears. And while my daughter is hardly timid, I have yet to see her initiate or even partake in a frisky wrestling match with her brothers.

I’m not exactly sure what kind of social construction goes on at the zoo. But as far as I could tell, it was hard not to see the similarities between those of us on either side of the glass. Those gorillas aren’t called our cousins for nothing.