Jet set mice:
Not long ago I mentioned the idea a friend had offered that some of the decline in fertility among modern rich countries may be that we bathe so much we wash away our sexy body odors. (Yuck. All right. I know. There is a yuck factor to marrying cousins, even distant ones. Life is yucky. Live with it.) Here is another.
Electric lights have made an enormous amount of difference in how much time we stay away, particularly how late we stay up. It might not be directly related but a recent study (Jet Lag Disrupts Pregnancies in Mice SCIENCE vol. 336 no. 6085 June 1, 1012 page 1083) on mice is interesting. They accustomed the mice to artificial light and then shifted their days forward by six hours every five to six days. They got up six hours earlier and turned in six hours earlier every shift of the time. The result was that successful pregnancies dropped from 90% to 22%. It only took four time shifts.
When time was shifted the other direction the pregnancies did a lot better. I think general wisdom is that it is easier to travel west than east. Staying up a little late and lying in bed a little late are easier than going to bed early and getting up early.
My recollection is that even a shift from daylight to standard time and back increases the death rate in humans, particularly older people. So ones circadian clock is nothing to be taken lightly.
Not many of us jet off to Europe for parties very often and even fewer then continue east following the parties all the way around the globe. But a lot of us do shift work. I can tell you from my own experience that totally chaotic wake and sleep cycles make you miserable. When I was living through the worst of that I swear my toenails began to suffer. Instead of nails they became yellow spongy clumps.
So is artificial light plus gripping drama on television altering our pregnancy outcomes? I doubt there is a lot of that. We’d know. There might be a little. It might be contributing to the rich world demographic decline I suppose.
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