If you could only have one child, would you prefer it to be a boy or a girl? Honestly? Here it is: 40 percent of Americans prefer to have a son and only 26 percent a daughter. This is the result of the Gallup poll of 1947 and -- hold your breath -- of 2011. The Gallup researchers have asked Americans a variation of this same question ten times since 1941, with little variance in the result. Oh, boy! Do prejudices ever change? Let's take a closer look: In 2011, 49% of men want a boy, women essentially have no preference. So, it's a guys' thing, is it? Shockingly, it's also an age thing: Americans who are younger than 30 say they would prefer a boy to a girl by a 54% to 27% margin. That boy-preference gap declines to 12 points among those 30 to 49, to 5 points among those 50 to 64, and finally to only 2 points among those 65 and older.

The anti-girl bias is in fashion -- not only in America, but around the globe. It is unclear how far Americans are willing to go to act on their gender preference, but new technologies such as artificial insemination and in vitro fertilization make it as easy as stock picking for hopeful parents to choose their favorite sex. Thus far, most attention has been focused on Asia, where, by the sheer population numbers, these kinds of decisions have a devastating effect in tilting the global gender balance. Last year, the Economist reported a "war on girls," counting 100 million missing baby girls worldwide. Recently, the Philadelphia Inquirer pointed out that the demographic shift will have major consequences in the decades ahead.

I think we need to ask a broader question and understand the reasons: What's behind it? Why, sisters, why?

Let's take a look at Asia, where the girl bias is most obvious, and most deadly. As its latest 2011 census reveals, India counts 914 girls younger than six years for every 1,000 boys. If nobody interfered, only a few more boys than girls would be born. If I do the math right, this means that in India alone, 500,000 girls are not allowed to live -- every year. The numbers in China, with its strict implementation of the one-child-family, are even worse.

These are staggering figures, and a rather recent development. In India, it is the flipside of an emerging India with a new middle class, a higher literacy rate, better health care. Until the sixties, the girl ratio in India was almost even. Now millions have new access to modern diagnostics, and this blessing can come with a curse. Middle-class parents get to know the gender of their baby through prenatal ultrasound, and they have a choice -- do they want to abort their baby girl and try for a boy instead? Economists thought that gendercide would decrease as the wealth in Asian nations increases, but the recent Indian census and other studies reveal the opposite: more and more parents opt for a boy. The truth is: it is not getting better for girls, it is getting worse.

"The problem is much greater than economics, education and lifestyle," says Glenn Fawcett, Field Executive Director of the nonprofit Lotus Outreach, who has worked in some of Asia's poorest regions for almost two decades. India has long banned gendercide, but law and family pressure are two different categories. Often, the pregnant women are pressured by their families to abort if they expect a girl -- especially if it is a first born. And even if they don't abort -- girls are less likely to be taken to a doctor when they get sick or get a good meal when food is scarce. Thus the girls' mortality is far greater than the boys'. In some cases, they are literally left to starve and die.

Glenn Fawcett suggests in Indian society the risk and burden of raising a girl is greater, no matter what caste or economic class. There is the dowry problem, but also a general view of seeing girls as less valuable, more of a liability than an asset. It is the boy who is expected to stay home, take care of his parents when they are elderly, bring home a good wife, and run the family trade. Girls, however, leave the house to take care of their husband's family, and if they elope or get pregnant before their marriage is arranged, the whole family's reputation is irreparably ruined.

While traditional customs and values are hard to shift, it is comparatively easy to suggest creative solutions in Asia. Lotus Outreach tries to change perception from the ground up: its programs specifically target girls' education. Every Indian girl who earns her own dowry is tipping the table. Every woman who gets a secondary education and thus a good job is the pride of her family. Every daughter who is able to support her family is a living proof that the girl bias is outdated. It can be done: South Korea, once boasting a girl ratio as bad as China's, has profoundly transformed itself and is heading towards equality now.

Yet, as the Gallup poll shows, the rift goes much deeper, beyond India's dowry customs and China's one-child policy. We just don't value girls as much, whether in Asia or America. Traditional perceptions in Asia might be hard to shift and easy to condemn, but with no dowry system and equal education access in America, why do American parents prefer boys, too?

Do parents feel more confident a son will care for them when they are old and bedridden? Wrong turn. As Nancy Folbre showed in the New York Times, daughters are more likely to be there for them. Are American parents afraid their daughter will get pregnant early? We don't know. Is it because American women are still likely to earn less than their male counterparts? You got a point there, but this is yet another argument for equal wages, not fewer girls. It is a puzzle, and a baffling one. We have more questions than answers. So, let me ask you, Americans: Why do you prefer boys? Or, what's so special about having a baby with a penis?