Why nail biters don’t cry
by Jonathan Sarfati and
David Catchpoole
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.’
The energy needed to cut through [our nails], is as much as what’s needed for horse’s hoofs
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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 horse’s 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).
References and notes
- Either accidentally or deliberately for grooming.
- Sanides, S., Nails and hooves: designed for wear and tears, The Scientist
18(4):12, <www.the-scientist.com>, 2 March 2004.
- Fingernails have the strength of hooves, New Scientist 181(2433):19,
2004.
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