This Slate article about American Asians and gender selection is interesting as a counterpoint to the "technology will solve everything" meme that permeates our culture.
Now comes further evidence of this effect. Two days ago, economists Douglas Almond and Lena Edlund published an article in Proceedings of the National Academy of Sciences examining the ratio of male to female births in "U.S.-born children of Chinese, Korean, and Asian Indian parents." Among whites, the boy-girl ratio was essentially constant, regardless of the number of kids in a family or how many of them were girls. In the Asian-American sample, the boy-girl ratio started out at the same norm: 1.05 to 1. But among families whose first child was a girl, the boy-girl ratio among second kids went up to 1.17 to 1. And if the first two kids were girls, the boy-girl ratio among third kids went up to 1.5 to 1. This 50 percent increase in male probability is directly contrary to the trend among whites, who tend to produce a child of the same sex as the previous child.*There's no plausible innocent explanation for this enormous and directionally abnormal shift in probability. The authors conclude that the numbers are "evidence of sex selection, most likely at the prenatal stage."
So some Asians in America -- or Americans of Asian descent -- are almost certainly using abortion to ensure that they get a boy. This process is enabled by technology: not only does technology make it possible, but advancing technology makes gender determination and selective abortions more private, which bypasses any opprobrium such an abortion might otherwise provoke.
I've written before that gender selection poses a philosophical problem for libertarians and an existential problem for the primarily Asian cultures that practice it. It's hard for me to see how technology will "solve" this quandary absent a culturally dominant moral worldview.
Peripherally, the sentence I starred above doesn't sound right to me. According to this article about an article about the National Longitudinal Study of Youth, the gender of later children is only very slightly affected by the genders of earlier children, if at all. Did the author of this Slate article, William Saletan, pull the starred statistic out of thin air, or is there other research on this topic I haven't been able to find with Google? Sounds like an old wives' tale to me.
Natural family planning data says that the time of sex relative to the female fertile cycle makes a difference in sex ratio's of children born - Males predominate early, females later. Perhaps your statistics show a difference in sexual style as more children are born?
tolonaro: Can you cite scientific evidence? I think that's just an old wives' tale.
evidently there is less agreement than I thought on the subject. There seems to be agreement that male/female sperm are different enough chemically that conditions could favor one or the other. I think there is enough evidence to require more investigation -- in your analysis as well.
Here is an example of a comment on the subject: first is the link then the particular comment which seems to summarize the discussion well.
http://parents.berkeley.edu/advice/pregnancy/conceptiongender.html
In reading the other postings to your question, I would like to add a slightly different perspective for the ''non-50:50'' crowd. I was reading a debate recently over whether one can use timing of intercourse with respect to ovulation to help select the gender of a baby. You've probably read about the more traditional ''X-chromosome sperm live longer, Y-chromosome sperm swim faster.'' A fertility specialist (sorry, I can't remember who) claims that the traditional idea about early intercourse increases the probability of a girl and intercourse right at ovulation increases the probability of a boy is not correct; from his work, he believes this timing is actually backwards. In either case, however, he goes into details about how the woman's cervix is positioned and what position intercourse is performed in, what the woman's particular biochemistry is (i.e., how acidic or basic her cervical fluid is) and how long sperm can survive in it can have an effect on the determining the gender of the baby conceived. There are also likely some differences in men's sperm and survivability, too. Thus, it sounds like there might be some room for when couples like to have sex with relation to ovulation, what position they have it in, and how long sperm tends to survive in vivo to send the odds of having a boy or a girl in one direction or another beyond a simple 50:50 ratio for a particular couple. These preferences and chemistries could be entirely unconscious, and could result in a couple being more likely to have a baby of a particular gender. Apparently, a number of health care workers agree, based on the other postings about a 70 to 80% chance of having a baby of the same gender of two older siblings. However, based on one other posting, it does sound like there is not unanimous agreement on the potential to slant the odds away from a simple 50:50 among doctors and nurses. anon