Saturday, August 29, 2009

What'll it be? Sons or Daughters?

I wonder whether these two would have sons or daughters? Picture via here.

I was reading the October issue of Psychology Today yesterday and came across an article entitled A Chip off the Best Block by Satoshi Kanazawa, Ph.D. It was an interesting read, with the author arguing that the sex of babies is partly determined by factors in the parents' life-- factors such as their beauty, brains, wealth, and sexual promiscuity.

I won't get into it too much, but this theory rests largely on the Trivers-Willard Hypothesis which predicts that wealthy parents have more sons while poor parents have more daughters. As evolutionary biologists, two scientists (Robert Trivers and Dan Willard) argued that it makes more sense for wealthy parents to have sons as sons can reproduce more than daughters, and as they have more money, they can better support their offspring. The son of poor parents is less likely to find mates as his poverty is a discouragement, whereas their daughters, if beautiful, can still marry "up" in the food chain (so to speak).

Here is where it gets interesting though. Using that basis, Kanazawa has expanded the hypothesis to include other factors that help in determining whether a couple has daughters or sons. Here are some of the factors Kanazawa suggests:
  • "Male" brains beget sons while "female" brains beget daughters. Male brains are good at figuring things out, and examples of people who possess strong male brains are engineers, mathematicians, and scientists. Female brains are good at empathizing, and examples of people with female brain are nurses, social workers, and schoolteachers.
  • Tall and big parents have more sons (since size is more a benefit for men than women), while short and small parents have more daughters.
  • Violent parents tend to have more sons (since historically violence was a main means of survival for men).
  • Physically attractive parents are more likely to have more daughters than sons since, according to Kanazawa, physical attractiveness is more beneficial to women in long-term and short-term mating.
  • Sexually promiscuous parents have more sons than daughters which is a trait more beneficial to sons as they can drastically increase their number of offspring by being promiscuous whereas daughters will only produce one child a year.

So, if you have higher social status, greater wealth, a strong "male" brain, larger body size, a tendency toward violence, or a tendency toward sexual promiscuity, then you're more likely to have a son. If, on the other hand, you have lower social status, lesser wealth, a strong "female" brain, smaller body size, and are physically attractive, then perhaps you should be stocking up on the color pink.

Thought that was interesting and had to pass it on...



Ad Tys said...

seems feasible he has a point

Leif said...

I can't comment on his other work, but I found a paper by a statistician and a sociologist that gives some warnings about Kanazawa's "beauty" paper:

"the classical 95% interval for the effect of parental attractiveness on the probability of a female birth is [-3.9% to 13.3%]. To put it another way, effects as low as -3.9 or as high as +13.3 percentage points are roughly consistent with the data. Given that we could begin with an expectation that effects were in the range +/-1%, we have essentially learned nothing from this study."

"The point of these examples is not to single out particular pieces of research for criticism. They are illustrations of a more general problem: that the structure of scientific publication and media attention seem to produce a bias toward overstating the magnitude and certainty of effects found in small studies. Journalists are naturally attracted to startling results and can downplay qualifications or uncertainties."

"Moreover, the estimated effect grew during the reporting."

In summary, caveat lector when it comes to popular articles about research on small samples.

elventryst said...

Leif and Ad, thanks for commenting! I had my own doubts as well, but I'm a sucker for anything that could make an interesting blog post (I'm such a slave to my blog, and after having taken a hiatus all summer long, I am eager to get it back up and running).

cyrus said...

That entire article is illogical! Moral character, behavior, or physiology cannot be demonstrated to be the determining factor in the gender of offspring.