Which of the following is an example of stabilizing selection?

Stabilizing selection is a type of natural selection that favors the average or intermediate phenotypes within a population, reducing variation and maintaining the status quo for certain traits. Infant birth weight is a prime example of stabilizing selection because there is optimal birth weight associated with higher survival rates. Babies that are born excessively small may have higher risks of mortality due to underdeveloped organs, while excessively large babies may face difficulties during birth, potentially harming both the infant and the mother. Thus, the evolutionary pressure results in most infants being born at a weight that is ideal for survival, which ensures that those weights are favored over time.

In contrast, variation in bird beak sizes represents directional selection where different beak sizes can be advantageous depending on the available food sources. Coloration in butterfly species may show disruptive selection, where individuals at both extremes are favored over average phenotypes. Lastly, tree height in a forest may depend on various selective pressures such as competition for sunlight, which can yield a different selection dynamic. Therefore, infant birth weight most exemplifies stabilizing selection as it directly points to the maintenance of an optimal trait in the population.