Why nail biters don’t cry
Scientists have just found out what you always wanted to know: why do fingernails, when nibbled or torn,1 tend to tear across the nail rather than downwards towards the nail bed? University of Manchester researcher Roland Ennos is a habitual nail biter. Maybe that’s why he (along with other researchers) tested the toughness of snippets from students’ fingernails.2 They found it takes twice the energy to cut them lengthwise as it does crosswise.
And that’s just as well, says Ennos. ‘Otherwise, we would be in agony throughout our lives, because every tear would damage our nail bed, inflicting great pain and incurring infection.’
Fingernails are unique to humans and other primates. They not only protect the top of our fingertips, but also help keep the skin at the tips of our fingers in place, making it easier for us to hold and manipulate objects. And now Ennos and his colleagues, analyzing nails under the electron microscope, have identified why nails don’t tear toward the nail bed.
Nails comprise three layers of tissue containing the protein keratin. The central layer was found to have keratin fibres parallel to the half moon at the base of the nail. These fibres stop breaks from running down the nail. The two outer layers have randomly arranged keratin fibres, and they provide strength.
How much strength? ‘The energy needed to cut through [our nails], is as much as what’s needed for horses’ hoofs’, says Ennos. ‘It’s quite amazing.’3
So, fingernails are as strong as horses’ hooves! Zoologist John Gosline, of the University of British Columbia, has seen the same orientation of cracks in horses’ hooves as in human fingernails. ‘Nails and hoofs are external structures that experience a mechanically stressful environment’, he says, explaining why the orientation of fibres is so important. In the case of horses, if cracks were to run upwards instead of across, it could lead to infection, laming and death.
How could anyone say that this crucial design feature of hooves and fingernails has come about separately in horses and humans by accident—the result of evolution? The evidence surely shouts of a Designer (Romans 1:20).
We are indeed most fearfully and wonderfully made (Psalm 139:14).
Re-posted on homepage: 22 February 2023