Human Limits

Earlier this week a piece in the New York Times reviewed some ideas about how “genes” might influence political thinking and explain why people vote the way they do.  Like many studies the observations underpinning the assertions about genes and politics rely on comparisons of traits between identical and fraternal twins or perhaps other closely related family members. Since identical twins are genetically identical, the fact that their political attitudes are more similar than fraternal twins is use as evidence that at least some elements of political belief systems are hard wired by genes.

 

There a number of obvious holes in this argument that parallel those raised in a previous post about genetics of talent.  The two most obvious are the shifty definitions of what is a gene and also the inability of people to find discrete snippets of DNA that account for most human characteristics.  A great recent example of this problem is from a paper looking at the ability of a large number (more than 60) snippets of DNA to help accurately predict the risk of diabetes.  This study found that it is hard to find specific DNA signatures that tell you much about who gets diabetes.  We know diabetes is highly heritable, and it is pretty easy to diagnose who is or is not diabetic based on simple clinical tests.  However knowledge about DNA does not help much if at all.  If we can’t use DNA to predict who is at risk of diabetes, how can we expect to find DNA based explanations for things as complicated as who is at risk for being conservative or liberal?

 

The Environment Matters

Like diabetes a lot of people will tell you that high blood pressure is heritable.  However, take a look at the graph below from a study of the Kuna people from Panama.  This study shows that depending on where the Kuna live, there are vast differences in the rates of high blood pressure as people age.  So, a genetically homogeneous group of people who live in traditional ways on an Island have essentially no high blood pressure, those who live in a tight community (Kuna Nega) in Panama City have a rate of ~30% in those over 60, and the Kuna living all over Panama City have a rate of 40% in those over 60.  In the groups living in Panama City there are also more young people with high blood pressure.  If you plugged the blood pressure values from people like the Kuna into data analysis programs that estimate heritability and thus the “genetic risk” of various things, you will get wildly different answers depending on the sub population you study.

 

 

Whenever Anyone Says “It’s Genetic”…..

The take home message in all of this is that whenever you hear that some complex human trait “is genetic”, remember a few things:

1)    The definition of a gene has shifted and many of the ideas about heritability date from the pre DNA definition of what exactly a gene is.

2)    For things that are pretty easy to measure like height, weight, blood pressure and diabetes it has been hard to get clear cut DNA signatures that explain much.

3)    The environment, behavior and culture matter. A whole lot of thinking about how much of what is heritable depends on the environment and not differences in DNA.

 

So take assertions about what is genetic with a grain of salt.

 

 

This entry was posted on Friday, July 11th, 2014 at 4:58 am and is filed under Current Events. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.