Does your job choose your baby’s sex?
Apparently, parents who are in stereotypically “masculine” professions such as physics, accounting or engineering are more likely to have a baby boy than those in nursing or other more “feminine” jobs.
This is interesting enough that I went back to the original article [ I doubt that link will work in general. The reference is: Kanazawa and Vandermassan, Journal of Theoretical Biology, 233(4) pp589-599 (2005)] They were exploring a proposed explanation for autism - that there exists “the “male brain,” which is particularly designed for “systemizing,” and the “female brain,” which is especially suited for “empathizing.” The systemizing brain, as you’d expect, is all to do with understanding the underlying laws of a system, whether that’s mathematics or how to play darts. The empathizing brain, again as you’d expect, is all about understanding emotions and responding appropriately to emotional triggers, understanding what people are thinking. The theory seems to be that men typcially have systemizing brains (”Type S”), while women have empathizing (”Type E”), which gave them specific evolutionary advantages (hunting/tools/etc and making friends within new groups respectively). Basically, it’s just putting the (perhaps justified) stereotypes on a more physiological footing, I think. It’s suggested then that autism may result when someone has an excessively male-type brain, and so excel at certain tasks, but may not have “normal” social skills. This explains many, but not all, of the clinical signs of autism.
Anyway, the upshot of this is that the researchers wanted to look at the correlation between professions (which should in turn correlate, even if weakly, with brain type, particularly, they claim, in the U.S. where people are reasonably free to choose the job best suited to them) and the sex of the children in order to investigate the heriditary connection. They found that parents in engineering, science and mathematics are more likely to have sons, while therapists, school teachers and nurses are more likely to have daughters. The odss seem about 130 boys to 100 girls for male professions, and visa versa for the females. Furthermore, having more sons results in having fewer daughters, with all other variables controlled for, and visa versa. So that really seems to suggest that if you’ve had one son, your chances are actually higher of having more, and the Malcom in the Middle family of four boys perhaps isn’t as unlikely as it seems! They suggest that as males typically have systemizer brains, they’ll tend to have male children, and similarly for females - so as a couple, they battle it out for brain type dominance! Two mathematicians are more likely to give birth to a boy, while two nurses are more likely to have a girl. A physicist with a therapist, or two more “average” professions will have a 50/50 chance, as you’d typically expect.
They’re very cautious about interpreting the cause of their results, and what conclusions could be drawn. One suggestion is that the level of hormones (e.g., tetosterone) in both parents plays a role in determining the sex of the baby. I don’t really understand this myself - I’m not sure if they’ve established a link between hormones and “brain type”. But there really does seem to be something there - their results are quite convincing, at least to a non-specialist like myself.
Of course, the media has promptly taken things one step further and suggested that “Couples desperate to produce a son could boost their chances if one or both of them switches to a “masculine” profession such as engineering or accountancy”. Perhaps this is true - but that might be reading more into the report than is good for it.
Whatever Says:
Er, some basic gradeschool science shows that the the female partner contributes nothing to determining the sex of the child. Remember the male sperm, with either an X or a Y chromosome?
Anonymous Says:
However, an Evolutionary Biologist could easily argue that some traits in the female could predispose her to marry someone of a similar brain type (ie - engineers spend more time around other engineers and scientists, which may make type E people more likely to marry a type E). Furthermore, her genes will clearly contribute to the brain type of her offspring so the system does not break down just because the female does not chromosomally determine the sex.
lulu Says:
There is some evidence (although I’m not sure if it works in humans) that the female/egg has some ability to do ’sperm selection’ although its unclear what is being selected for.
gradeschool science Says:
Gradeschool science isn’t sufficient, whatever; vaginal acidity helps determine the proportion of the weaker Y sperm that survives. So both partners influence the gender of offspring.
Anonymous Says:
Unfortunately, to the best of my knowledge, no one has ever proved that one type of sperm or the other is “weaker” or that acidity has any effect. There are theories along those lines, but they tend to be (at best) unproven.
Joel Says:
That’s one thing I find really interesting about all this - how could there be selection? It might be an interesting side result that there really is some sort of sperm selection going on during fertilisation.
electrical engineer Says:
Interesting… I’m an Electrical Engineer - 3 girls, two boys….
Your babies' daddy Says:
So who’s the father?
Chuckle Says:
LOL - that got a laugh out of me! Congratulations with the big family, by the way… Five children. So what does your wife do?
My parents were both teachers, and they got 3 daughters and 1 son. My brother went into economics (mathematics), my sister in veterinarian medicine (science/empathy), my other sister in business (HR management), and I am a technical translator (language/engineering). Go figure.
Brewer Says:
Before we start explaining what the underlying cause of the phenomenon is: has anyone checked on HOW MANY subjects the experiment was conducted? If this was only the 130+100=230 people I doubt that the research has any statistical value, as very often happens with this kind of research. Please accept my apologies if you can show me (without paying 30 bucks to see the article) that statistical requirements are met: hypothesis, uncertainty introduced by way of measurement, how this uncertainty is derived (we are dealing with people with different lives) et cetera.
bubba, the real bubba Says:
“I’m not sure if they’ve established a link between hormones and “brain type”.
Check out all the literature on digit ratio 2D:4D and personality traits…
Joel Says:
Good point! Although, while that’s an indicator of the amount of tetosterone you’ve been exposed to, does it really correlate to brain type?
bubba, the real bubba Says:
It’s statistally significant, and N looks to be about 738) see below.
…and BTW even if it were 130+100 it would be right on the borderline…
data: 100 and 230
number of successes = 100, number of trials = 230, p-value = 0.05561
alternative hypothesis: true probability of success is not equal to 0.5
95 percent confidence interval:
0.3697542 0.5015140
sample estimates:
probability of success
0.4347826
———————————————————————-
The effects of respondents’ brain types on the sex of their offspring (Generations t and t+1)
Dependent variable
Number of sons Number of daughters
Main predictors
Systemizing occupation .3498** .1357
(.1326) (.1341)
Empathizing occupation .2684 .3981**
(.1405) (.1411)
Trivers–Willard controls
Education −.0375** −.0571****
(.0142) (.0142)
Income −.0187* .0063
(.0073) (.0074)
Risk factors
Age .0325**** .0278****
(.0031) (.0032)
Age at first marriage −.0519**** −.0415****
(.0082) (.0083)
Race (1=black) .2979** .4998****
(.1150) (.1149)
Currently married (1=yes) .1688* .1363
(.0735) (.0741)
Number of sons/daughters −.1029** −.1044**
(.0366) (.0371)
Constant 1.4699 1.3036
(.2633) (.2665)
R2 .1952 .1620
n 738 738
Note: Main entries are unstandardized regression coefficients.
Numbers in parentheses are standard errors.
*p
JT Says:
Anybody think maybe this is reversed? Maybe it is not that people in “masculine” jobs are more likely to have sons, but that people more likely to have sons often end up in more “masculine” jobs and vice-versa. It is hard for me to believe that changing jobs would change the propensity of having a particular gender child. But the opposite I could definitely see. Whatever sum of mechanisms governs the propensity for gender of child is likely to have an affect on “brain” gender and thus lead to a higher propensity for a “masculine” or “feminine” career.
Joel Says:
I totally agree - I think the media missed the boat on this one, and that it seems unlikely that changing jobs would suddenly start producing more sons. The only possibile way I can see that occuring is that if you switched from nursing to mathematics, and started thinking in a “different” way, then you generate more hormones/etc which then influence the sex of your child. But I don’t think that’s justified anywhere.
jbssm Says:
Well … what a an obvious misuse of statistics.
You see, last time I’ve checked humans beings have 2 parents.
Now, there are the cases in favor in witch both or just one of the parents do have a profession in accordance with the gender of their child.
But only one case against (both parents have a profession that is not in accordance with the gender of the child).
Seems obvious why this numbers appeared, they have got nothing strange with them.
ajo Says:
It is also possible that the female body might change the chances that the Y sperm get to fuse with egg.
Truck and Barter Says:
Employment is Destiny?
Those of you toiling in a more “masculine” profession and are expecting, it looks like you might be more likely to be saying “Atta boy!” Blokey jobs encourage baby boys, study says The conclusion comes from a survey of 3,000 people from various pro…
Hairsplitter Says:
So rather than testosterone levels perhaps systemizing brains are genetically corelated with stronger or acidity-restistant Y sperms in males and lower vaginal acidity in females, and conversely E type brains correlated to weaker Y sperms and higher acidity?
Or could high vs low levels of testosterone imply all of the above?
Anthony Staines Says:
Typically, there are a number of major statistical errors.
1) No indication of whether, or how they coped with both parents being included in the survey, that is non-independence in the data. This is a killer mistake.
2) Use of normal theory regression for Poisson/binomial data (counts of children). This is less important, but suggests a failure to think clearly about the question being addressed.
If they fix their analysis this might be worth looking at…
Peter Says:
What really matters is not the size of the overall sample, but the size of the subgroups involved. If only 5% of the 3,000 work in the most “masculine” professions, not an unreasonable assumption if we’re talking about the proportion of mathematicians, enginers, and physicists in the US population at large, then the relevant sample size on which the dependent measure is based is 0.05*3000 = 150. Public opinion polling reports also often suffer from these types of errors. A sample size of 1,000 sounds like a lot, but when you end up comparing the attitudes of, say, 18-24 year-old males to 18-24 year-old females, apparently “big” differences often turn out to be within the margin of sampling error.
Anonymous Says:
there are 2 kinds of people out there, those that think that there are two types of brains, and those that don’t
Chris Says:
I’m a teacher and my wife is a nurse-the child was a boy.
My obersavations of couples and children have actually led me to the opposite conclusion ie the more ‘manly’
the man the greater chance of a female child.
alaskandesign Says:
I don’t think it is saying that your offspring are determined by your occupation.
“to look at the correlation between professions (which should in turn correlate, even if weakly, with brain type, particularly, they claim, in the U.S. where people are reasonably free to choose the job best suited to them) and the sex of the children in order to investigate the heriditary connection”
The reason they are using the occupation is because when given the choice of occupation, Type S will likely choose certain professions while Type E will choose much different types. What is truly being compared is brain type and offspring.
Paul Lemma Says:
Hm,did they just look at the “wussy” male desk jobs, or did they also consider construction, heavy machinery, prison guards, military, and so on?
Joel Says:
Actually, by “male” jobs, they mean jobs that correspond to the type of brain that is (supposedly) more common in men, the analytical “systematic” type brain, which is needed for jobs such as engineering, mathematics, etc. Prison guards, labourers, etc may or may not have that type of brain, and would probably have been classed as “neutral” in their study.
Chuckle Says:
Like any such study, it probably needs to be taken with a grain of salt. Other studies widely publicized in sensationalist newspapers suggest that since males have, on average, a larger skull (and a proportionately bigger brain), they might have more brain power. :-/ If we run away with that conclusion, this of course supports the highly chauvinistic assumptions that women are less apt at decision-making, etc.
Anecdotally, some of the most intelligent people I have ever met were rather small built and had proportionately small skulls… ;-)
What is interesting with this study is that it does publically present social skills (a stereotypically female characteristic) as a type of intelligence (insight). I would agree with that concept, even though people skills are not usually measured by IQ tests, which focus on more measurable aspects of intelligence: analytical skills and memory.
Another interesting hypothesis is the idea that both male and female offsprings of highly analytical people would **tend** to be analytical also, which would support the nature-over-nurture theory. Of course, we know from experience that such slight statistical tendencies have little bearing on people’s lives since there are plenty of examples of scientists coming from regular households, and vice versa. :-) The nurture-over-nature theory also has corroborative evidence (e.g. the life choices and performance levels of adopted children compared to those of their biological parents). This study might also be influenced by sociological factors, like the opportunities available in a particular region at a particular time (local opportunities influence our career choices–even in the US).
As I see it, this type of study is only useful for attempting to explain extreme variations in human beings (usually pathological ones). Even when it tries to explain the origin of autism, this study does not provide any absolute answer, just a hint… If its conclusions are true, it might indicate that genetic variety is good within a couple, as in society–too much of a good thing leading to dysfunction.
Bill Jefferys Says:
This may be simply due to a statistical error. See Andrew Gelman’s blog for details:
http://www.stat.columbia.edu/~cook/movabletype/archives/2006/04/amusing_example.html#comments
Guess it’s all boys for me.
In light of my niece’s birth yesterday, I thought this article was interesting. It gives a summary of this recent paper in the ever-so-boringly-named Journal of Theoretical Biology that describes the statistics of parents with either empathizing occu…