Body Hair.pdf
(
486 KB
)
Pobierz
Body hair
The not-so-naked ape
Human body hair, once thought to be an evolutionary
relic, has a real job to do
Dec 17th 2011 | from the print edition
MUCH
ink and
many
Good night. Sleep tight. Mind the bugs don’t bite
electrons have been spilled on the question of human hairlessness:
why, as Desmond Morris put it in the title of a book published in 1967,
Homo sapiens
is “The Naked Ape”. This lack of hair has been attributed
to everything from a putative aquatic period in the species's past to the
advantages of displaying a healthy skin to members of the opposite
sex.
Less attention has been paid, though, to the fact that humans are not
really hairless at all. Per square centimetre, human skin has as many
hair follicles as that of other great apes. The difference is not in the
number, but in the fineness of the hair that grows from those follicles.
These fine human hairs do not seem to be performing any of the
functions of their counterparts in more hirsute species (insulation and,
www.economist.com/node/21541808/print
1/3
through colouration, either signalling or camouflage). So what are they
for?
That is a question addressed by Isabelle Dean and Michael Siva-Jothy
of Sheffield University, in Britain, in a paper in
Biology Letters
. Their
conclusion is that humans have fine body hair to serve as an alarm
system.
Ms Dean and Dr Siva-Jothy were testing the idea that fine body hairs
(known, technically, as vellus and terminal hairs) are there to alert
their owner to creepy crawlies such as bed bugs, which might be intent
on biting them, and that the hair may also get in the way of such
arthropods' activities, giving the owner more time to react before he is
bitten.
The standard “lab rat” for this sort of experiment is the university
student, and Ms Dean and Dr Siva-Jothy managed to recruit 29 eager
volunteers for their study—19 men and ten women. Each had a patch of
skin on one arm shaved, marked with a pen and surrounded by
petroleum jelly (to fence the bed bugs in), and a commensurate patch
on the other marked and surrounded, but not shaved.
It was then time to get the bed bugs out. The bugs in question had
been fed a week previously, and then starved, so they were eager to
eat. Volunteers were asked to look away while a researcher put a bug
on one of the skin patches. The volunteer was then supposed to record,
using a press-button counter, the number of times he perceived the
insect moving on his skin.
The difference was significant. When the bug was on a hairy patch it
was detected, on average, every four seconds. When it was on a
shaved patch, more than ten seconds elapsed between detections.
Moreover, the bugs seemed to find it harder to locate a good spot to
bite when they were surrounded by hair. Though no volunteer was
actually bitten, because the vigilance of the watching researcher meant
the insects were removed when they extended their probosces prior to
biting, bugs on hairy skin took about a fifth longer than those on
shaved skin to attempt to bite their hosts.
In both cases men (who are hairier than women, as measured by the
density of follicles and the length of the vellus hair) were better off
than women when the bugs were released on unshaven patches of skin,
though there was no significant difference between the sexes when
they were shaved. The upshot is that, whatever the reason why human
www.economist.com/node/21541808/print
2/3
body hair has shrunk, one reason it has not disappeared completely is
because it warns and protects those who sport it from the attentions of
hostile insects.
from the print edition | Science and technology
Copyright © The Economist Newspaper Limited 2012. All rights reserved. Accessibility
Privacy policy Cookies info Terms of use
Help
www.economist.com/node/21541808/print
3/3
Plik z chomika:
Rainhardt
Inne pliki z tego folderu:
Body Hair.pdf
(486 KB)
Cancer Drugs.pdf
(208 KB)
Epigenetics and Health.pdf
(475 KB)
Restarting Hearts.pdf
(213 KB)
Synthetic Biology.pdf
(463 KB)
Inne foldery tego chomika:
Zgłoś jeśli
naruszono regulamin