In a study that followed more than 400 women just as they were starting to try to get pregnant, the researchers found that women with the highest levels of the stress indicator alpha-amylase in their saliva were 29% less likely to get pregnant than women with the lowest levels.I'll check my audacity enough to admit that I'm not certain I understand either, but I'll hazard a seemingly obvious though politically incorrect guess: Reproductive fitness.
They also found that women with the highest levels of alpha-amylase were more than twice as likely to meet the clinical definition of infertility--meaning they did not get pregnant even after a full year of trying.
Alpha-amylase is associated with our fight or flight response, but it can still be chronic, said Lynch.
"When you think 'fight or flight' you think acute response, but what most people don't know is that if you are chronically stressed, your body will learn to keep that system hyperactive," she said. "It has learned you are under attack constantly."
The researchers still do not understand exactly why stress affects a woman's ability to become pregnant, but this study did rule out some possibilities. For example, they found women with high levels of alpha-amylase had the same amount of sex as some of their less-stressed counterparts. "It's not that stressed out women have less intercourse," she said.
There are countless stress triggers in contemporary western society that don't have obvious parallels with pre-industrial human history, but the biological consequences of excessive stress haven't changed much. If a woman is hand-to-mouth and even that existence is precarious, it's probably not an optimal time for her to stretch her meager resources--biological, psychological, material, and otherwise--by additionally becoming responsible for her own delicate genetic future at the current moment.
Female reproductive investment is substantially larger than male reproductive investment is. And not just in terms of time and energy spent, but also in terms of opportunity cost--in becoming pregnant, women give up nearly a year of their reproductive lives, while men give up fifteen minutes of theirs, which are decades longer to being with. Waiting for the sources of the stress to dissipate is, genetically, often the better bet for women. Let me go out on a limb here, since I'm not able to verify this empirically, and presume that stress--or a lack thereof--has more influence on female fertility than it does on male fertility (though it seems plausible that it also has the potential to effect the latter).
Political correctness makes us collectively dumber. A corollary to that is the assertion that factoring human biodiversity into our thought processes makes us more insightful.