On 1 Oct 2004 07:46:23 -0700, (Bruce
Jackson) wrote:

wrote in message . ..

Okay, you asked for it.

A zebra is a black animal with white stripes.

Occasionally, you get a zebra whose white stripes fail to
form properly and are dashed, white dots and blotches
instead of solid white stripes.

How do we know that such zebras suffer from white stripes
failing to form vs. black strips that grew together?

Dear Bruce,

The white blotches, dots, and dashes on the oddball zebra
appear to be partially formed white stripes on a black
background. There is no apparent narrowing of the white
stripes consistent with the alternate theory of expanding
black stripes, just the look of dashed white highway
stripes.

So in zebras, white stripes are caused by inhibition of dark
pigment.

The whole essay in "Hen's Teeth and Horse's Toes" is worth a
look. (The preceding essay is also about zebras.)

If nothing else, you'll learn that there are three species
whose striping patterns differ according to when the
striping begins during fetal development.

Zebra striping is most notably different on the rump, which
expands markedly during the fifth week of fetal development.

So if the stripes are laid down before this expansion, they
expand into big stripes, but if the striping occurs after
the fetal rump has expanded, they will be narrower and more
numerous.

Gould lacked the courage to speculate about whether female
fetal zebras worry about the stripes making their butts look
big, but I think that we may reasonably infer that this is
one of the causes of the notorious irritability of the
creatures.

Carl Fogel