Why are male ferrets so much larger than females?

Many thanks to Bob Church, who wrote this section as well as most of the others. Bob has studied biology and archaeology and is currently pursuing a Ph.D. at the University of Missouri, Columbia. Bob writes: I have several male ferrets that are twice as large and three times heavier than the females. This phenomenon [different shapes and/or sizes for males and females] is called "sexual dimorphism," and occurs in most species to one degree or another. Sometimes, the females are larger (some birds, spiders, etc.) But in most sexually dimorphic mammals, the males are larger than the females, some considerably so. The reasons for this are varied, but three of them apply to mammals in general, and one in particular in the case of the polecat and ferret. One reason is sex. The biggest guy gets the girl, so big guys produce more offspring compared to little guys. This works to a degree--until the limits of the niche are met--otherwise animals would only get bigger and bigger. Also, it ...  more