“I am particularly concerned about ways in which contemporary reproductive behavior and biology may be a mismatch with the reproductive lives of our ancestors.” DR. WENDA TREVATHAN, ANCIENT BODIES,MODERN LIVES
A Battle All Her Own
In my classes, semester after semester, I made the statement that while men’s lives have changed greatly since the Paleolithic era, women’s lives have changed exponentially over that same time period. That fact has potentially dire consequences for young women. It has only recently been realized that these drastic lifestyle changes could have dramatic effects on women’s health.
In Ancient Bodies, Modern Lives, Dr. Wenda Trevathan has framed the situation compellingly and logically. She points out that before birth control was invented, women had relatively few menstrual cycles. As pointed out elsewhere in Battles of the Sexes, most of their reproductive lives were occupied with being pregnant or breastfeeding. Many of them may have had only 160 menstrual cycles over their entire lifetimes, compared to up to 450 for present day women in Western societies. She concludes that women’s reproductive physiology may not be optimally adapted to the routine monthly fluctuations of estrogen and progesterone that happen during a typical menstrual cycle. She quotes reproductive biologist Roger Short, who essentially says that since natural selection has worked over the eons of the past to maximize reproductive potential, women are physiologically ill-suited to spend the majority of their reproductive lives in a non-pregnantstate.
A Life Without Tampons
To explain further, the typical life of one of our ancestral women would include having her first period around 16 years old. It would happen this late because her foraging lifestyle would have been so active, and the resulting amounts of food gathered so relatively small, that the body fat build-up required to signal a girl’s body to start ovulating would happen much later than it does today. She would have had about three years of non-ovulatory, and therefore non-fertile, cycles and then would have had her first conception around her 19th birthday. This would have been followed by about three years of on-demand breastfeeding. Because of the on-demand breastfeeding and its effect of being a natural birth control mechanism, she would have had her next child about four years later.Following this pattern, she may have had up to six children with perhaps four of them surviving to reproduce. The final child she may have nursed for four years or more,and this would have taken her into menopause, with the passing of her menstrual cycle barely noticed by her or her husband.
In twenty-first century, Western nations, this scenario is becoming exceedingly rare. Since the early 1800s, there has been a steady decline in the age at which girls experience their first period. Many of them begin menstruating at age 12 or younger. As a result, many start experimenting sexually and may become pregnant as early teenagers before they are even finished growing themselves. Others use birth control to put off pregnancy until their 30s, 40s, or even altogether. Breastfeeding and Cancer Prevention Another difference from ancestral women is that breastfeeding, if undertaken at all, now lasts less than a year. Since breastfeeding is usually not on-demand these days, it does not prevent ovulation from re-starting. Through these methods, many modern women limit their number of children to two or three. This unnatural situation leads to, as noted earlier, modern women experiencing nearly three times as many menstrual cycles as our early ancestors. During every menstrual cycle, because of the exposure to estrogen and progesterone cells in the breast and uterus in crease their turnover rates in preparation for a possible pregnancy. Each time a cell divides, there is the opportunity for a cancerous mutation to take place. Therefore, these higher cell turnover rates create more chances for mutations.
Also,the excessive surges in estrogen impact estrogen-related cancers of the breast, uterus, and ovaries. All of this mismatch with our ancestral environment leads to an estimated rate of breast cancer for modern women that is one hundred times higher than ancestral women or women from present-day foraging populations who don’t practice birth control as we do in Western societies. This represents another battle of the sexes that is a result of our cultural mismatch with our genetically encoded biological inheritance. The impact of that mismatch on Western society’s women’s health and well-being is largely unrecognized and underappreciated. It also, of course, impacts all of those who care about and love those women.