It's All About Surface Area and Reproduction
You have a 50/50 Chance of Getting the Right Answer
Let's face it, as educators, parents, and adults we don't have answers to all the "whys" that come our way. However, I've found that there are two answers to almost any question in biology: sex and surface area (and is usually all boils down to just sex and reproductive success). I know this sounds funny, but if you remember this rubric, while leading guided hikes in the field, in class or teaching animal anatomy, you will always have a way to root out the answer you're looking for.