Sexual dimorphism is a big word that seems complicated.  But, in reality it is just a way of explaining why males and females of some animals are different sizes or colors.

The world and the Rocky Mountains are full of so many amazing animals of all different shapes and sizes.  Many times I have seen animals and just knew that male bears or moose tended to be bigger than females, but never really thought about it.  There is, however, a reason for the differences in sizes, shapes, and colors of animals.  The phrase that describes these differences is sexual dimorphism.

What Is Sexual Dimorphism?

It is what scientists have discovered explaining why some males and females of the same species look different than each other.  The differences could be in size, color, or shape.  Importantly, these differences were passed on in the genetic material of the species.  That means the differences were things that the babies received from their parents.

As I’ve talked about in the past, everything in life comes down to a quest for survival – meaning to reproduce.  The explanation for why males and females of some animals appear so different than each other comes down to the choices that the females made for a mate.

In some animals the females may have begun to choose males that possessed certain characteristics or appearances.  Those same characteristics would then be passed on to their babies.

An Example To Show How Sexual Dimorphism Works – Mallards

A good example is the common mallard or duck.  The males of this species tend to have colorful breeding plumage while the females remain brown.  Males become colorful in an attempt to attract females so that they can mate.  Over time (thousands of years) the females have chosen the more colorful males.

Since the more colorful males are the ones having babies, their children will also tend to be more colorful.  Thus, over time there are more and more colorful males.   Then over a very long period of time the male mallards all tend to have brighter colors than the females.

Examples of Sexual Dimorphism in the Rocky Mountains

Male moose grow huge paddles or antlers on their heads for no reason other than to win a mate.  Read these other cool moose facts.

Honey bees – Queen bees are much bigger than the small male drones that do nothing other than to reproduce with the Queen.

Grizzly bears – males are usually much larger than females.  They can grow up to 850 pounds while females only grow up to 450 pounds.