HUMAN nails are as strong as a horseās 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, āI 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, thatās very, very unusual.ā So Ennosās team armed with special scissors and tweezers, tore and cut nails, and studied them under a scanning electron microscope.
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Nails are made up of a sandwich of three layers of keratinous tissue. And Ennosās team found that it is the central layer ā which has keratin fibres arranged parallel to the half moon at the base of each nail ā 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).
āThe energy needed to cut through [our nails], is as much as whatās needed for horsesā hoofs,ā says Ennos. āItās quite amazing.ā
