DO ZEBRAS HAVE STRIPES?
In a column about animal color patterns, you noted that researchers
have given several different explanations for why zebras have stripes.
I went to the internet to check out scientific articles about zebra
striping but found them very confusing so eventually gave up. What are
the generally accepted explanations? And out of curiosity, do any of
them refer to Rudyard Kipling's "Just So Stories" and his
brief but charming explanation for why a zebra has stripes?
One reason you might have difficulty interpreting most scientific explanations
for why zebras have stripes is that virtually all of the studies are
inconclusive in explaining the adaptive significance of the stripes.
No conclusion is categorically better than any of the others.
and most common scientific explanations were related in some way to
camouflage. More than a century and a half ago, the biologist Alfred
Russell Wallace proposed that the striping made zebras less conspicuous
at night when they went to waterholes. The contrasting pattern would
also be effective in some forest situations or in tall grass. Charles
Darwin challenged Wallace's explanation by noting that zebras standing
out on an open, short grass plain would be obvious to lions and other
predators. Darwin's criticism seems a bit simplistic, but as he was
Charles Darwin ...
idea has persisted and one suggestion is that zebras evolved in partially
shaded forested areas where the stripes served as camouflage. However,
many zebras now inhabit the open plains but have not yet lost their
stripes. The stripes in this case are considered holdovers from an earlier
time. One recent proposal is that the stripes have neither a value nor
a cost to a zebra in the open so no strong natural selection exists
to alter the current genetics.
effect, which can be considered a form of camouflage, has been offered
as an intriguing idea for how a herd of striped zebras might escape
from a predator. In this situation the striped pattern creates moving
vertical lines difficult for a lion or a leopard to focus on. Thus the
entire herd can sometimes escape before an individual has been singled
out for capture by a confused cat.
proposal that has not gotten much traction among zebra biologists has
been the thermoregulation hypothesis. Black stripes and white stripes
absorb the sun's rays at different rates, with the black stripes getting
hotter than the adjacent white ones. This creates a subtle but persistent
airflow across the body of a zebra, resulting in a cooling effect over
the skin. Another idea that has been tested experimentally is that the
black-and-white pattern serves in some way to deter tsetse flies and
other biting insects. And of course with any species, individual recognition
is critical in a social group. Perhaps zebras recognize striping patterns
the way we recognize faces.
taken in several summary articles about zebra striping is patently incorrect.
In referring to Kipling's "Just So Stories," some authors
assert that Kipling addressed how the leopard got his spots and the
camel his hump, but he never explained the zebra's stripes. Wrong! "How
the Leopard Got His Spots" explains why the zebra became striped
- camouflage in the forest, so the leopard couldn't find it. As Mr.
Kipling put it, "And after another long time, what with standing
half in the shade and half out of it, and what with the slippery-slidy
shadows of the trees falling on them, the Giraffe grew blotchy, and
the Zebra grew stripy ..."
answer for why zebras have stripes is that each of the scientific hypotheses
has merit, some more than others but collectively they confer an adaptive
advantage and survival value to a zebra. This doesn't advance much beyond
what Kipling, Wallace or Darwin offered but seems as suitable an explanation
as any based on the facts as we know them today.
you have an environmental question or comment, email