More Females Born Near Equator
Every year there are more males born than females. However, new evidence shows that the ratio becomes much closer in populations that live near the equator. The findings holds true even when the data from some Asian and African countries are excluded. In these rare cases the data cannot be considered truly representative of the birth rate as the intentional abortion of female children is known to occur there. The study, conducted at the University of Georgia, evaluated dozens of indicators to determine the socioeconomic status of each of the 202 countries. There seemed to be no real correlation between socioeconomic status and female birth rates, but there was a correlation between latitude and birth rates. Countries with national capitals closer to the equator showed a smaller gap in the birth ratio of boys and girls. The difference was greatest when going from the tropics (within the 23 degrees of the equator) to the temperate regions ( within 50 degrees from the equator). The largest percent of females born occurs in Africa with 49.3% and the lowest occur in Asian and Europe with 48.6%. No one is really sure why this happens, but there are some possible reasons. There may be some correlation between temperature and birth rate or maybe sunlight affects the rate. There may be a genetic tool within humans that causes more female offspring to be produced during long, warm days just like in hamsters and mice. However, there is no explanation that seems to have hit the nail on the head yet. Why do you think less males and more females are born near the equator?
Update
There have been many comments about the fact that these percentages vary by too small of a degree, but we must remember the vast scale that these numbers represent. While the differences are only about .5%, there are over six billion people on earth, which makes that half a percent a lot more significant. The fact that both humans and mice give birth to more females during long, warm days may be an indication of a genetic trigger that is shared by all mammals. I think this was a really fascinating study that should be followed by more studies on other creatures to see if this really is a common trait among all mammals.
-Calin Darabus
Group B
posted by PWH @ 10:47 PM
9 comments
9 Comments:
I'm interested in the temperature/sunlight theory. Ostensibly the theory is that temperatures and sunlight discrepancies trigger changes in genes and gene products to alter behavior in humans. But when we think about it, females will give birth after a lengthy 9 months, and unlike other mammals, we have no breeding season and will have kids any time of the year. Given the 9 month gestation, mothers will be exposed to 3 out of the four seasons, each of which range sizably in terms of temperature and sunlight exposure, meaning there should be no real correlation between the two and birth ratios.
I would bet the answer lies in population evolution and some random advantage to populations with more males.
[Nathan Beck, Group A]
This is interesting. I definitely want to know more about this. The percentage difference between the most females born and the least amount seems so small. Even though it is so small, I guess it must have lots significance to it.
Shonneau L.
This is really interesting! I wonder what tests they have done to conclude that in hamsters and mice, they have more female offspring when the temperature is higher. Also, are there any real ways to try and control whether you have a boy or a girl? Is this only found in humans near the equator? I totally agree with Nate on his idea too. Do the seasons have any impact on the females being born?
-Alyson Paige
Interesting article. May possibly add to the explanations of the overpopulation occurring in Africa and the declining population in Europe. Increase in female population may cause general population increase meanwhile an increase in male population would not.
-Julio Rodriguez
That is a crazy correlation. Actually, turtles (i think specifically sea turtles, but it might not be only specific to them)have temperature dependent eggs. when they are buried under the sand the ones towards the top of the surface are girls and the eggs more on the bottom are colder and will be boys. Perhaps it's the same with humans! How bizarre.
- Maura Mulvey
Hey Calin,
I think your blog is very interesting and it got me wondering why more females are born near the equator in comparison to males. I wonder if this only applies to humans or does it apply to animals as well?
You mentioned that in some countries, female abortions are done intentionally. I really find that disgusting and immoral.
Saad Choudhry
I agree with some people that the gap between the two percentages is pretty small, is it really certain that this difference is significant enough to make this correlation?
Nicholas Skvir, group C
It's pretty cool that is phenomena exists. It seems like maybe it could be a long lost remnant of when amniotes first diverged from other species in the tree of life. There are other species which use temperature as a decider of sex and it only seems logical that the same situation could still occur subtlety, or whether an ancient gene still lingers in our population evading selection.
-Conor Stenerson
The sunlight theory might make sense. I'd have to no more about it to really be sold on the idea. Is there any other species (besides us) that experience more females near the equator?
Crystal Cabral
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