Women tend to have smaller babies when men are scarce

Women tend to give birth to underweight or premature babies in places where women outnumber men; putting these babies at greater risk for heart disease, hypertension, and diabetes. This was the conclusion of a study conducted by University of Michigan School of Public Health researchers led by assistant professor Daniel Kruger and which was published in the American Journal of Human Biology. According to a Time magazine report, Kruger and his team compared the birth records of over 450 counties in 2000 from the U.S. Centers for Disease Control and Prevention against the 2000 Decennial Census data. They found a direct association between high rates of low birth weight or underweight births in counties where men were relatively scarce. Kruger believes that trend supports the “life history trade-offs” principle in evolutionary biology.  According to this theory, each major event in our lives come at certain costs (like growth, sexual maturity, or reproduction) and each of us only has a “finite amount of effort” or resources to “pay” for the costs of these life events. So to make the most out of our finite resources, we shortchange some events that happen during unfavorable circumstances in order to allocate more resources to other events that occur during more favorable circumstances. The best analogy for this would be how we sometimes scrimp on our day to day expenses (save our limited resources) so we can splurge once we go on vacation. Kruger believes this subconscious system of regulating birth outcomes is a result of thousands of years of evolution.  In the case of places where men are scarce, the mothers’ unconsciously make trade-offs based on their current life conditions: lack of supportive partner and the difficulties of raising a child alone. — DVM, GMA News