Tuesday, April 21, 2009

Sex ratios seem to vary by latitude

This is an interesting tidbit from the New York Times today - although more boys than girls are born all over the world, the ratio seems to be smaller among people living nearer to the equator. And no one is sure why. There are obviously many factors that influence the skewed sex ratio, but latitude is interesting because it's purely natural - it's not a cultural or economic factor like diet, selective abortion, or war.

Strangely, the researcher conducting the study found that "African countries produced the lowest sex ratios — 50.7 percent boys — and European and Asian countries had the highest with 51.4 percent.The effect of latitude persisted across wide variations in lifestyle and socioeconomic status. There were large differences in sex ratio between tropical regions within 23 degrees of the equator and the temperate regions 23 to 50 degrees north or south, but no difference between the temperate regions and the subarctic north of 50 degrees." And apparently, data that might have been changed by abortion or the killing of baby girls was excluded.

The scientists say that it may have something to do with evolution - or that it might have something to do with the quality of sperm at different temperatures. And some scientists pointed out that it's virtually impossible to tease out the effects of poverty and other conditions, so the study may be fatally flawed. But if it's true, it's an interesting puzzle - what do you think?

5 Comments:

At April 21, 2009 at 3:31 PM , Anonymous Anti-racist said...

Are you *sure* we want to start talking about biological differences between different human groups? We all know that race is a social construct, and while a tiny change in sex ratios might not be important in itself, it's just a hop, skip, and a jump to much more racist conclusions.

 
At April 21, 2009 at 7:18 PM , Blogger Christina said...

While biological/physiological differences, big and small, shouldn't matter one bit with regard to rights, respect, human dignity, etc., it's still important to recognize differences that do tend exist from a health/medical perspective. For instance, certain genetic disorders are more common in certain ethnic communities, and the amount of melanin your skin produces has implications for how much sunscreen you need to wear and how much vitamin D you need to consume. It would be a disservice to ignore the fact that people's ancestry leaves them at higher risks for certain diseases, disorders, health problems, etc. You do well to point out that there is a fine line between being aware of a prevalence or tendency for a specific genetically/biologically derived trait within a community and using that prevalence or tendency as a stereotype or in order to make value judgments, but that doesn't mean such things can't or shouldn't be considered rationally and without prejudice. I think, at this point, people are able to tell the difference.

At the same time, I think this study is not particularly open to racist conclusions. The region in question--23 degrees south to 23 degrees north latitude--includes Central America, most of South America, most of Africa, part of India, Southeast Asia, northern Australia, and very many Pacific islands. Considering that people of probably all races, ethnicities, etc., are represented in this set of regions, this seems to be a purely geographic category, not a biological or racial one.

On another note, the NYT article mentions that certain small mammals also produce more males at colder temperatures, and I know that with certain types of reptiles, the temperature at which the eggs are incubated helps determine sex ratios, so this trend seem to apply to more than just humans. This seems like a really interesting biological pattern worth exploring further.

 
At April 21, 2009 at 9:51 PM , Anonymous Anti-racist said...

Sure, this study's results will not make a splash at a KKK rally. But what I'm more concerned about is the long-term implications of studies like this. Every such discovery makes it easier to argue against the fact that "race" is a social construct and has no biological reality. There's no reason to believe, the racists will claim, that evolutionary racial differences stop at these esoteric diseases; ignorant people are already using Tay Sach's disease to argue that Jews are smarter, and that that has a genetic basis (http://www.latimes.com/news/nationworld/nation/la-sci-jewish-iq18-2009apr18,0,2228388.story)

What really concerns me is projects like HapMap, which tries to compile differences in genetic data between "races" just like Hitler's eugenists did. This pseudoscience may well produce "data" that gives racists even more ammunition.

I say we hold the line against this talk of group differences. Treating a few rare diseases is not worth the chance of giving racists ammunition to claim that West Africans are not just malaria resistant, but are genetically taller, or (worse yet) are more aggressive or have lower intelligence than whites.

 
At April 22, 2009 at 12:15 AM , Blogger Christina said...

At the same time, I'm sure the people with those rare (or not-so-rare) diseases would really appreciate being properly diagnosed and treated. Again, though, I don't see that this study is saying anything about race. It's about geographic groups that include people from numerous 'races.' It's not separating people into discrete communities and saying they're stuck there; it would be really interesting, in fact, if a study could track the sex ratios of children born to people who move into the tropics from temperate or sub-arctic zones and vice-versa.

Compiling differences is troubling, as is using genetic traits common to biological communities to draw conclusions and implications that, in fact, have nothing to do with the genetic trait being described. So I see your point. But I still don't see this study having long-term implications as far as providing arguments against the idea of race as a social construct. It'd be pretty hard to say that a study like this proves that races are discrete, when the trend is the same across all races.

On a side note, while race is not scientific fact, biological communities do exist, and are defined by ancestry and kinship, which are pretty indisputable (at least as far as we have knowledge of them). It's important to remember that for a very long time, people on the various continents in various countries had little to no contact with each other; for a very long time, the natives of the Americas didn't interact with Asians or Africans or Europeans; for a long time, Africans and Europeans and Asians didn't interact much, relative to population size, in such a way as to merge gene pools. For a very long time, peoples within each of those very broad communities didn't interact much with each other in such a way; even peoples living in the same geographic place may not have interacted much for long periods of time because of social and cultural differences and prejudices. Of course, all these different peoples are, to an extent, self-constructed--they all created their own societies with their own languages, cultures, etc., and had various degrees of interest in perpetuating their nation or their people or their society. Still, even granting that these groups of people were, to varying degrees, self-constructed, once people start reproducing, there are going to be biological consequences. Having largely separate, isolated gene pools for a long period of time does have implications for genetic inheritance, since you can only inherit the genes of your parents, who could only inherit the genes of their parents, etc.; the isolation of a gene pool entails that certain genes within that pool become ever more prevalent, and a lack of much interaction with other gene pools means that not many new genes are going to crop up. Acknowledging genetic inheritance based on ancestry or biological communities--by which I simply mean a group of people who share a common gene pool, as a result of being descended from the same people however long ago--doesn't entail saying that distinct races exist. There are surely hundreds, if not thousands, of biological communities within each so-called race.

Of course, as movement between countries and communities becomes ever easier, and as the world's population mixes more and more, the gene pool gets much more mixed up, so biological communities will tend to grow and grow and grow. That still doesn't preclude looking at the history of the biological community in order to glean useful and helpful information about health, genetics, etc. People who abuse such information in order to bolster false or shady claims about intelligence, personality traits, behaviors, etc., are abusing science, as anyone well-versed in science knows. The key, I think, it to educate people more so that they don't believe or fall prey to racist baloney, rather than to exclude potentially important avenues of discovery from our purview.

I may, however, be missing something. How do you see this study, specifically, as bolstering a racist viewpoint in the long term?

 
At April 22, 2009 at 9:25 PM , Anonymous Anti-racist said...

Racism asks one big question: Are there significant biological differences between the "races"? Every idealogue who trumpets these supposed differences makes the racist case a little bit easier to make.

 

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