Social Class and Life Expectancy
It is well known that people in the lower social classes on average die earlier than those in higher social classes. Obviously this could be due to factors of nature, nurture, or any combination thereof.
A new study by a reputable twin research unit in England casts some light on this. As reported by the BBC here, the study included some female MZ pairs who had married into different social classes. The results showed a significant difference in a physical indicator of ageing (telomere length), with those twins who married lower-class husbands ageing faster. As the twins have the same genes (quibbles about somatic mutations aside) this must be an environmental effect. The authors speculatively attribute it to the stress of lower social class life. Or maybe it is just the stress of marrying low class husbands??
An important caveat: the sample size is small, and another study is said not to have found significant effects.
I’m not sure, but there may be an inverse correlation between IQ and life span.
But since “stress” is unmeasured, how would one falsify the proposition?
A neglected issue in twin studies is that identical twins often differ in birthweight and thus also on childhood IQ (which is due to differential access to nutrition in the uterus depending on their positions).
These childhood differences may partly determine how much you study and who you marry. Therefore the assignment to partners is not random, and the health outcomes may even wholly be due to childhood differences.
So, I’d believe the result if they control for the twins’ birthweight. If not, I’m not convinced.
Economist: I think your problem is not with the result but with the interpretation. On your interpretation the difference is still environmental.
Mortimer says:
I’m not sure, but there may be an inverse correlation between IQ and life span.
See Gottfredson. The correlation is positive.
bioIgnoramus: Blood levels of the hormone cortisol are a proxy for “stress”. Not that it helps, since inborn differences almost certainly have major effects on cortisol levels.
Stress will always be an easy explanaton and a difficult independent variable.
Hans Selye invented the term stress when he discovered that he he could cause the same syndrome of symptoms from a wide variety of treatments. His rats died from stomach lesions if they had been put in the cold or worked too hard or put in a pyschologically frustrating learning situation. Same result – multiple causes. He invoked the mechanical engineering term “stress”. Got him a Nobel prize and gave everyone else a facile explanation for almost anything.
I am currently working on this problem by building a time machine. I’ll go back and kill Selye and thereby improve the language. Of course first I need to get rid of Einstein and thereby clear up this “it’s all relative” talk.
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Oops, what I meant to say was:
Stress will always be an easy explanation and a difficult independent variable.
Yeah. It seems that some of us have been given a leg up, in the form of two good alleles in the 5HTTPLR area, or some such.
(Cut-n-paste coding causes so many problems!)
Thanks, DN. And thanks too to Economist: how cheering to learn that there are circumstances where it is a good thing to be heavy.
The correlation is positive.
That’s what I meant – positive, not inverse.
“Of course first I need to get rid of Einstein and thereby clear up this “it’s all relative” talk.”
At which point your time machine disappears and you get yanked back into the present. Or you perhaps disappear altogether because your father or grandfather died in the invasion of Japan.
Anyway, if we can’t even nail down what stress is or what is or is not “stressful”, we can’t really say whether or not stress accelerates aging. And if we want to fix aging, we need to find the mechanism by which various things accelerate or decelerate it. Telling people to “avoid stress” is less than helpful.
“bioIgnoramus: Blood levels of the hormone cortisol are a proxy for “stress”. Not that it helps, since inborn differences almost certainly have major effects on cortisol levels.”
And on stress, at least as we commonly understand it. Thus cortisol levels may still be a good proxy for comparison between individuals.