21. Hair or fur is one thing mammals (哺乳动物) have in common. How thick that hair is changes for each animal. For example, elephant hair is four times thicker than hair from adult humans. Larger animals have thicker hair, says Wen Yang, a materials scientist at the University of California, San Diego.
These materials scientists study materials such as metal or plastics. They study what makes the material and how it works. The information helps scientists work out how to make better materials or how to create new materials.
Recently, Yang looked at mammal hair. She worked on how it holds up under stress. They looked at hair from eight different mammals, including humans. They reported their work in January 2020 in a scientific journal. Yang's team tested the
tensile strength of the hair. Tensile strength is how much you can pull something before it breaks. The scientists thought that thick hair would be stronger. But they were wrong.
"Interestingly, we find the thinner hair, actually, is stronger," Yang says.
The hair of adult humans was some of the thinnest hair in the study. It was also some of the strongest hair. The thinnest of all hair came from children. But it was even stronger.
Hair is made of keratin (角蛋白). It is a type of protein. Proteins form living cells. Keratin makes up hair and fingernails in humans. Keratin is made of two parts. The outside is the cuticle (角质层). It covers the inside, cortex (皮质), which is strong. The scientists used a microscope, a tool that helps us see very small things, to look at how keratin breaks. They found that thicker hair is easy to break. The cortex breaks are clean and straight. Thin hair is different. The cortex breaks are rough (粗糙的) and uneven. It takes more pulling to do this. So the thin hair is stronger than thick hair.