Hair is an amazing substance. Composed of a protein called keratin, hair is a unique structure found almost only in mammals – of which humans are one example. In fact, the presence of hair is one of the defining features of the biological classificatory order Mammalia, along with mammary (milk) glands. We’ve put together a collection of fascinating facts about hair and hair loss from the natural world – some of which might surprise you!
- Hair is the fastest growing tissue in the body, second only to bone marrow.
- Hair first evolved amongst a common ancestor of birds, mammals and reptiles that lived 310 million years ago. The substance alpha keratin first evolved as a component of claws (for which it is still used), but a subsequent mutation along the mammalian line lead it to form into hairs.
- The substance from which hairs are made – keratin – also forms part of horns, such as those sported by rhinos. This is why when a rhino horn is cut off, it eventually grows back!
- Humans aren’t the only mammals that experience hair loss. Certain other species of primate, such as chimps, stump-tailed macaques and the uakari, also progressively lose their hair after adolescence. Their condition is still known as Alopecia, as it is in humans. Stump-tailed macaques in particular have been used to study the causes of human baldness, as the mechanism by which they shed their hair is much the same.
- The male lions of Tsavo national park are notable for being maneless. They are also known for being more aggressive and for forming prides with more females per male than is usual. This is believed to be because the male lions of Tsavo have a higher level of testosterone, suggesting that lacking a mane is a sign of male dominance.
- Sea otters, on the other hand, have the densest fur in the animal kingdom, with up to 150,000 strands of hair per square centimetre. Long guard hairs keep the fur waterproof, while the undercoat traps air and keeps in body heat. In order to maintain this waterproof coat, sea otters need to keep it scrupulously clean, and are therefore able to groom their entire body. They even blow air into their coats, in order to add to the insulating effect!
- The various sloth species of South America have a greenish tint to their long fur – but this isn’t due to pigmentation! Because they move so slowly, they actually have algae growing in their hair. This doesn’t bother the sloths though – in fact, it helps camouflage them!
- Polar bears don’t actually have white fur. The outer layer of guard hairs that cover their body are actually transparent; they only appear white because of the way they scatter light (rather than by reflecting it, as white fur would).
- Many mammals living in temperate or polar environments change their pelts with the seasons to assist with camouflage. The Artic Hare, Arctic Fox and Ermine (or Stoat) all do this. They achieve this by moulting their brown or mottled summer coats in autumn, replacing them with a white winter coat underneath. This is then moulted and replaced with a fresh summer coat the following spring.