Annie Murphy Paul wanted her second child to be a boy. She announces this in the first sentence of Chapter 5 of “Origins: How the Nine Months Before Birth Shape the Rest of Our Lives,” where she writes:

I want a boy. Is it all right to say that out loud? I want a boy because I already know about girls. Growing up I had one sister, and 30 female classmates at my all-girls’ school; childhood was a clutter of hair ribbons and Barbie shoes, adolescence a mist of Secret deodorant and Love’s Baby Soft perfume. I knew almost nothing of boys until I gave birth to one, which may be why they captivate me now.

Is it O.K. to say it out loud? We have discussed that heatedly and often on Motherlode, and you can use the comments to continue the conversation. But first, Ms. Paul has a lot more to say about sex and gender, specifically about how different sexes experience the womb differently.

There is something, she writes, to some of those “old wives’ tales.” For instance:

Women who are pregnant with girls may indeed experience more nausea. … Several large investigations have found that women afflicted with severe morning sickness, called hyperemesis gravidarum, in the first trimester are more likely to be carrying a female fetus. Doctors, concluded one study, “can say with confidence to a woman who has hyperemesis gravidarum that she has a 55.7 percent chance of delivering a girl.” The sicker she is, the more likely this is to be true: a 2004 study by epidemiologists at the University of Washington found that women who were extremely ill (hospitalized for three days or more) had odds of having a girl that were 80 percent higher than those of women who did not experience severe nausea. A hormone called human chorionic gonadotropin may be to blame: female fetuses produce more of it than males.

Likewise, she continues, boys can make you eat more:

Obstetricians have long known that boy babies tend to be bigger than girl babies at birth, by an average of 3.5 ounces. But they weren’t sure how this difference came about. A 2003 study tracked the diets of more than 300 women receiving prenatal care at Beth Israel Hospital in Boston. Women who were pregnant with boys consumed about 10 percent more calories than those who were pregnant with girls: more protein, more carbohydrates and more fats, adding up to about 200 extra calories a day. Testosterone secreted by fetal testicles, the researchers speculate, could be sending mothers a signal to eat more. (Another possibility occurs to me: perhaps women who learn they’re carrying male fetuses are already obeying the cultural dictate to feed growing boys.)

Women just might have some sort of “sense” that tells them if they are having a boy or a girl:

… one small but intriguing study found that, “contrary to expectations,” women who rely on dreams and emotions to guess their babies’ sex have a surprisingly good chance of being correct. Among a group of 45 well-educated pregnant women — all of whom had chosen not to learn fetal sex from prenatal tests — 17 said they had a “feeling” about whether their fetus was male or female, and 13 were right. Eight of the women reported having a dream about their fetus’s sex, and every single one of them was on the money. “It is always possible that this was a spurious finding,” acknowledged the authors, from Johns Hopkins University in Maryland. “It is equally likely that there is simply much about the maternal-fetal connection that we do not know.”

So, fetuses of different sexes might just be sending different signals from the inside to the outside. But what about the other direction? Are there external influences that determine the sex of a child in the first place?

Nature usually provides a male-to-female ratio of 105 to 100. Except when it doesn’t. A thick blanket of coal smoke covered London in December 1952, so thick that people “couldn’t see their own feet, or more than a foot in front of their noses,” Ms. Paul writes, and more than 4,000 people died. Nine months later, area hospitals recorded 144 female births compared with 109 male. The ratio was similarly skewed after the East German economic collapse in 1991, the Kobe earthquake in 1995 and the attack on the World Trade Center in 2001. In each case, more girls were born than boys.

What besides national catastrophe has been linked to such natural sex selection? Among the triggers that have been studied are: stress (47 percent of those most distressed on Danish psychological tests had boys, while 52 percent of those who were least distressed did); single parenting (boys are slightly less likely to be born to women who are not living with a man at the time of conception); skipping breakfast (women who ate cereal every morning at time of conception had a greater chance of delivering boys).

Now, let’s say that, like Ms. Paul, a woman wants a child of a certain sex. What to do to influence gender before pregnancy?

There are attempts recorded back to Greek times, Ms. Paul reports: lying on one’s right side, binding the left testicle, or biting the woman’s right ear during sex. There is no evidence that any of these actually worked. Equally unproven is the theory that intercourse three days before ovulation will produce a girl, while waiting until the day of will result in a boy, but that lack of evidence has not kept the book suggesting the method, “How to Choose the Sex of Your Baby,” from selling 1.5 million copies since it was published in 1970.

Ms. Paul, who tried none of these approaches, gave birth to the boy she so badly wanted.

Which leads back to the original question: Is it all right to say that out loud?