What Kind Of Selection Shapes Human Birth Weight?

Human birth weight exemplifies stabilizing selection in biology, a phenomenon that has been observed for centuries. This natural process ensures the survival of newborns by favoring a moderate birth weight range, typically around 7 pounds. This optimal weight range strikes a balance between two extremes: underweight babies who historically had a higher risk of not surviving and overly large babies who could lead to life-threatening complications during pregnancy. Therefore, stabilizing selection operates to maintain the prevalence of babies with a birth weight close to this median value, safeguarding their chances of survival and overall well-being. This concept has been a fundamental aspect of reproductive biology for centuries and continues to be relevant in modern medical practice. [Date: March 10, 2021]

Stabilizing selection in birth weight refers to a natural evolutionary process in which the average or mean birth weight of a population is favored. In the context of humans, babies born with exceptionally low or high birth weights face elevated mortality rates. Consequently, the selective pressure favors babies with birth weights close to the population’s average, as these infants are more likely to survive and thrive. This phenomenon underscores the importance of maintaining a balanced birth weight range within a population for the overall health and survival of newborns.