What Color Is a Zebra? 
Is it a white animal with black stripes? Or vice versa? 
by Stephen Jay Gould 
Some persistent, unanswered ques- 
tions about nature possess a kind of ma- 
jestic intractability. Does the universe 
have a beginning? How far does it ex- 
tend? Others refuse to go away because 
they excite a pedestrian curiosity but 
seem calculated, in their very formula- 
tion, to arouse argument rather than in- 
spire resolution. As a prototype for the 
second category, I nominate: Is a zebra 
a white animal with black stripes or a 
black animal with white stripes? I once 
learned that the zebra’s white under- 
belly had decided the question in fa- 
vor of black stripes on a blanched torso. 
But, to illustrate once again that 
“facts” cannot be divorced from cultural 
contexts, I discovered recently that 
most African peoples regard zebras as 
black animals with white stripes. 
In a poem about monkeys, Marianne 
Moore discussed some compatriots at 
the zoo and contrasted elephants and 
their “strictly practical appendages” 
with zebras “supreme in their abnor- 
mality.” Yet we learned last month that 
the three species of zebras may not 
form a group of closest relatives — and 
that stripes either evolved more than 
once or represent an ancestral pattern 
in the progenitors of true horses and ze- 
bras. If stripes are not the markers of a 
few related oddballs but a basic pattern 
within a large group of animals, then 
the problems of their construction and 
meaning acquire more general interest. 
J. B.L. Bard, an embryologist from Ed- 
inburgh, has recently analyzed zebra 
stripes in the broad context of models 
for color in all mammals. He detected a 
developmental unity underlying the 
different patterns of adult striping 
among our three species of zebras and, 
inter alia, even proposed an answer 
to the great black-and-white issue 
in favor of the African viewpoint. 
Biologists follow a number of intel- 
lectual styles. Some delight in diversity 
for its own sake and spend a lifetime de- 
scribing intricate variations on com- 
mon themes. Others strive to discover 
an underlying unity behind the differ- 
ences that sort these few common 
themes into more than a million spe- 
cies. Among searchers for unity, the 
Scottish biologist and classical scholar 
D’Arcy Wentworth Thompson ( 1 860— 
1948) occupies a special place. D’Arcy 
Thompson spent his life outside the 
mainstream, pursuing his own brand of 
Platonism and packing insights into his 
thousand-page classic On Growth and 
Form — a book so broad in appeal that 
it won him an honorary degree at Ox- 
ford and, thirty years later, entered the 
Whole Earth Catalog as “a paradigm 
classic.” 
D’Arcy Thompson struggled to re- 
duce diverse expressions to common 
generating patterns. He believed that 
the common patterns themselves had a 
kind of Platonic immutability as ideal 
designs, and that organisms played 
with constrained variations upon them. 
He developed a theory of “transformed 
coordinates” to depict variations as ex- 
pressions of a single pattern, stretched 
and distorted in various ways. But he 
worked before computing machines 
could express such transformations in 
numerical terms, and his theory 
achieved little impact because it never 
progressed much beyond the produc- 
tion of pretty pictures. 
As a subtle thinker, D’Arcy Thomp- 
son understood that emphases on diver- 
sity and unity do not represent different 
theories of biology, but different 
aesthetic styles that profoundly influ- 
ence the practice of science. No student 
of diversity denies that common gener- 
ating patterns exist, and no searcher for 
unity fails to appreciate the uniqueness 
of particular expressions. But alle- 
giance to one or the other style dictates, 
often subtly, how biologists view organ- 
isms and what they choose to study. We 
must reverse the maxim of the repro- 
bate father teaching his son morality — 
do what I say, not what I do — and rec- 
ognize that biological allegiances lie not 
so much in words but in actions and 
subjects chosen for research. Note what 
I do, not what I say. Of the “pure tax- 
onomist” — the describer of diversity — 
D’Arcy Thompson wrote: 
When comparing one organism with an- 
other, he describes the differences between 
them point by point and “character” by 
“character.” If he is from time to time con- 
strained to admit the existence of “correla- 
tion” between characters ... he recognizes 
this fact of correlation somewhat vaguely, 
as a phenomenon due to causes which, ex- 
cept in rare instances, he can hardly hope to 
trace; and he falls readily into the habit of 
thinking and talking of evolution as though 
it had proceeded on the lines of his own de- 
scription, point by point and character by 
character. 
D’Arcy Thompson recognized, with 
sadness, that the theme of underlying 
unity had received much lip service, but 
little application. Differences between 
the striping patterns of our three zebra 
species had been described minutely 
and much energy had been invested in 
speculations about the adaptive signifi- 
cance of differences. But few had asked 
whether all the patterns might be re- 
duced to a single system of generating 
forces. And few seemed to sense what 
significance such a proof of unity might 
possess for the science of organic form. 
The vulgar version of Darwinism 
(not Darwin’s) holds that natural selec- 
tion is so powerful and pervasive in 
scrutinizing every variation and con- 
structing optimal designs that organ- 
isms become collections of perfect 
parts, each minutely crafted for its spe- 
cial role. While not denying correlation 
in development or underlying unity in 
design, the vulgar Darwinian does rele- 
gate these concepts to unimportance 
because natural selection can always 
break a correlation or remold an inher- 
ited design. 
The pure vulgar Darwinian may be a 
fiction; no one could be quite so foolish. 
But evolutionary biologists have often 
slipped into the practice of vulgar Dar- 
winism (while denying its precepts) by 
following the reductionistic research 
strategy of analyzing organisms part by 
part and invoking natural selection 
as a preferred explanation for all forms 
and functions — the point of D’Arcy 
Thompson’s profound statement cited 
above. Only in this way can I make 
sense of the curious fact that unity of 
design has received so little attention 
in the practice of research — although 
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