Sex Ratios ...
This from Linda...thoughts?
In class today, we talked about the male and female differences in birth, and I found an interesting paper on the topic. It talks about a relationship between partnership-status and resultant offspring sex. The writer of the paper found a ratio which correlates to what we were speculating would be the percentage: when the mother had a spouse/partner, there was 51.5% male births. However, the percentage was 49.9% male births mothers who weren't living with a spouse or partner at conception. Anyways, while this paper doesn't exactly explain the genetics involved, it provides some support for the idea of conditions impacting the success of male vs. female babies.
Comments
Are those numbers really significant? Saying that 49.9% of babies born to mothers who are not living with a spouse or partner are boys doesn't seem that significant to me. Is this really different from the 50.1% of girls who are born to mothers not living with a spouse or partner?
Posted by: Anonymous | May 14, 2006 04:39 PM
I just realized that the link doesn't take you to the original page. If you type in "sex ratio partnership-status" into the search bar, it will come up with the abstract, then on the left module just hit "open entire document".
As for the percentages, I can see how perhaps it may not seem significant but the paper discusses that after analyzing with logistic-regression models, they found that partnership status was the only factor that was statistically significant. The paper also said that children whose parents were together were 5.4% more likely to be male, which, while I'm not sure how it reconciles with the percentages above, is indicative of an increased likelihood of male births to partnered parents.
Posted by: Linda Tan | May 15, 2006 12:35 AM
Check out this page, found by professor Keen.
http://www.cia.gov/cia/publications/factbook/fields/2018.html
Stats here show the number of males per 1 female. Note that males outnumber females in every country, most notably in Armenia, but the ratio there does an about face after age 15. Check out the bio on Armenia and see if you can come up with an evolutionary explanation.
Posted by: Whiting | May 15, 2006 04:58 PM
This is really interesting, the bios on these countries. But I think an evolutionary explanation would be that boys perhaps are more vulnerable than girls, and to counter this the birth rate is higher. Not as a question of value, but perhaps boys are more susceptible to childhood diseases, or maybe in our evolutionary past, infanticide (this is all speculation) than girls are. That would explain the steady decline in the sex ratio as the age of the population increases. The ratio for the total population is .9 males per 1 female, which, when compared with the 1.17 males/female at birth, shows that the males die off first.
Posted by: Linda Tan | May 18, 2006 03:50 PM
Perhaps the change in the ratio around age 15 has something to do with risk-taking? If males are more prone to violence, homicide, etc., then it might be possible that, overall, males will die earlier due to stress or just being shot.
Or, it might be possible that the change in the ratio has something to do with war. Males tend to enter actual combat more than females do, and this may play into a decrease in the male populations.
Posted by: Eugina Huang | May 18, 2006 11:10 PM