Hair

Hair is one of the defining characteristics of mammals, but how much do you know about it? Get to know your hair a little better

Hair
image by Paul Lequay

Hair and fur are the same thing but the normal length of a hair is an individual and species-specific trait. So, across the breadth of mammals, there are many norms for hair length, or fur length. What’s really different is the pattern of where it grows. Your dog or cat is basically covered with hair, whereas humans tend to grow hair in a few selected places. And that’s one of the things that have changed through evolution in a number of mammal groups. Whales, for instance, are mammals, but they are nearly hairless.

Most evolutionary biologists believe that the evolution of hair is correlated with the evolution of endothermy, or warm bloodedness, that is the ability to produce internal body heat, and hair is a very good insulator. If you’re going to spend a lot of metabolic energy heating your body, its more efficient to hold on to that heat and not to lose it to the environment around you. So, having hair as a means of insulation is one of the theories as to why we have hair. Of course, there is no way for us to tell whether hair evolved first and then endothermy, or whether endothermy evolved and then somehow hair evolved.

Female horses, called mares, carry their young for approximately 11 months, and a young horse, called a foal, can stand and run shortly following birth. Most domesticated horses begin training under a saddle or in a harness between the ages of two and four. They reach full adult development by age five, and have an average lifespan of between 25 and 30 years. While most horses are domestic, others remain wild. Feral horses are the descendants of once-tame animals that have run free for generations.