First Reader: Higher Hormone Levels…What’s Next?

Chapter 8 written by Tessa M. Pollard and Nigel Unwin describes the effect of westernization on a woman’s reproductive function. In Western populations (populations that are developed and industrialized), higher levels of hormones such as estradiol and progesterone can be found in a female’s body compared to non-Western populations. With these higher levels of ovarian hormones comes an increased risk for breast cancer, as well as a higher level of insulin resistance. Ovarian function has been found to affect insulin resistance. This is in addition to the prominent presence that obesity has of influencing insulin. Obesity is linked to Type II diabetes.

            Back to looking at how reproduction is affected: elevated hormone levels seem to be a negative consequence of westernization. If this leads to impairment of reproduction and ovarian function, why have high hormone levels not been selected against evolutionarily? Perhaps less-developed countries are better off with lower levels. Women in non-Western populations are not affected in their quality of life in this way as are Western women. Not only are these functions influenced, but hyperinsulinemia can also result, leading to elevated risks for certain types of cancer. I would assume that natural selection would lower hormone levels over time if all of the above is in fact the case, although the opposite appears to be true. Why is this not the case?