HUMAN nails are as strong as a horse鈥檚 hoof. And it is this structural strength that allows us to grip, scratch and even make those horrible nail-on-a-chalkboard screeches, without damaging our nails.
Only primates evolved finger and toenails, probably to provide better grip on tree trunks and branches.
Roland Ennos and his team at the University of Manchester, UK, wondered what gave the nail its structural properties. He says, 鈥淚 have always been a bit of a nail-biter, and I noticed that whenever you bite your nails, they never break into the quick of your skin. And for a material, that鈥檚 very, very unusual.鈥� So Ennos鈥檚 team armed with special scissors and tweezers, tore and cut nails, and studied them under a scanning electron microscope.
Advertisement
Nails are made up of a sandwich of three layers of keratinous tissue. And Ennos鈥檚 team found that it is the central layer 鈥� which has keratin fibres arranged parallel to the half moon at the base of each nail 鈥� that prevents breaks from running down the nail rather than across it. And the randomly arranged keratin fibres in the two outer layers give each nail its bending strength (Journal of Experimental Biology, vol 207, p 735).
鈥淭he energy needed to cut through [our nails], is as much as what鈥檚 needed for horses鈥� hoofs,鈥� says Ennos. 鈥淚t鈥檚 quite amazing.鈥�