One of the greatest things I have from my grandfather is a collection of wooden duck decoys. There are about a dozen different-sized, hand-carved duck pairs. My kids – who often visit my office where the decoys live on a bookcase – like to mismatch all the pairs, placing a bufflehead with a canvasback, a blue-winged teal with a common goldeneye. After the kids leave, I put all the pairs back together, and this time as I placed the male and female mallards side by side, I wondered: why is it that the male duck gets such elaborate, colorful plumage? While the female duck is nearly all light brown, and, frankly, rather drab? At a quick glance, these two look drastically dissimilar, and the untrained eye could think they were not the same species.
It turns out that differences like these in the same animal species are known scientifically as “sexual dimorphism.” Sexual dimorphism is the condition where the two sexes of the same species, like the boy and girl mallard, exhibit different characteristics – beyond just the differences of their sexual organs. The condition occurs in many animals, insects, birds and even some plants.