females also rank higher than larger 
males if the discrepancy in size is not 
too great. 
Although the female hyena’s as- 
sumption of what are usually male 
roles in mammals is probably related 
to its evolution of sexual structures 
that mimic male organs, the link be- 
tween these phenomena is not imme- 
diately clear. It cannot have much 
to do with sexual performance itself 
for, if anything, the female “penis” 
is a hindrance to copulation until its 
opening enlarges and its form departs 
from that of the male. 
Kruuk suggests that the strong 
mimicry arose in connection with a 
common behavior in hyenas called the 
“meeting ceremony.” Hyenas live in 
clans that defend territories and en- 
gage in communal hunting. But in- 
dividuals also spend much of their 
time as solitary wanderers searching 
the landscape for carrion. To maintain 
the cohesion of the clan and to keep 
strangers away, hyenas must develop 
a mechanism for recognizing each 
other and reintegrating solitary wan- 
derers into their proper clan. 
When two hyenas of the same clan 
meet, they stand side to side, facing 
in opposite directions. They each lift 
their inside hind leg, subordinate in- 
dividual first, exposing either an erect 
penis or clitoris, one of the most vul- 
nerable parts of the body, to their 
partner’s teeth. They then sniff and 
lick each other’s genitals for ten to 
fifteen seconds, primarily at the base 
of the penis or clitoris and in front 
of the scrotum or false scrotum. 
Kruuk believes that the female clit- 
oris and false scrotum evolved to pro- 
vide a conspicuous structure serving 
for recognition in the meeting cere- 
mony. He writes: 
It is impossible to think of any other 
purpose for this special female feature 
than for use in the meeting ceremony. 
... It may also be, then, that an individual 
with a familiar but relatively complex 
and conspicuous structure sniffed at dur- 
ing the meeting has an advantage over 
others; the structure would often facilitate 
this reestablishment of social bonds by 
keeping partners together over a longer 
meeting period. This could be the se- 
lective advantage that has caused the evo- 
lution of the females’ and cubs’ genital 
structure. 
Speculation about adaptive signifi- 
cance is a favorite, and surely enter- 
taining, ploy among evolutionary bi- 
ologists. But the question, “What is 
it for?” often diverts attention from 
the more mundane but often more en- 
lightening issue, “How is it built?” 
In this case, speculations about adap- 
tive significance have been in the lit- 
erature for a long time, yet no one 
bothered to tread the obvious path 
for hypotheses of anatomical construc- 
tion until 1979: What sexual hormones 
are maintained at what levels by fe- 
male hyenas from conception to ma- 
turity? (See P. A. Racey and J. D. 
Skinner, “Endocrine Aspects of Sex- 
ual Mimicry in Spotted Hyenas, Cro- 
cuta crocuta,” vol. 187, Journal of 
Zoology, 1979, pages 315-26.) 
Racey and Skinner found, in short, 
that two androgens (male-producing 
hormones) had higher concentrations 
in testicles than in ovaries of adult 
spotted hyenas (scarcely surprising). 
Yet, when they investigated levels of 
the same hormones in blood plasma, 
they detected no differences between 
males and females. One female con- 
tained two twin female fetuses, and 
both, despite their tiny size relative 
to their mother, contained about the 
same level of testosterone as adult fe- 
males. Racey and Skinner therefore 
conclude “that high foetal androgen 
levels are responsible for the appear- 
ance of the male sexual facies in adult 
female spotted hyenas.” 
Confirmation for their hypothesis 
arises from their study of brown and 
striped hyenas, the other two species 
of the family Hyaenidae. Neither 
brown nor striped hyenas develop peni- 
form clitorises or false scrotums. In 
both species, androgen levels in blood 
plasma are much lower for females 
than for males. (Aristotle, by the way, 
defended hyenas against the charge 
of hermaphroditism by correctly de- 
scribing the genitalia of these other 
species — something of a dodge with 
respect to the spotted hyena, the 
source of the legend, but “the master 
of them that know” was right in any 
case.) 
But why should high levels of an- 
drogenic hormones lead to the build- 
ing of false penises and scrotums. The 
animals that construct them are still, 
after all, genetically female. How can 
female genes produce mimics of male 
structures, even under the influence 
of unusually high levels of androgenic 
hormones. A look at the developmen- 
tal basis of sexual anatomy resolves 
this dilemma. 
Mammals share a common pattern 
for the embryology of sexual organs, 
and we may therefore use humans as 
an example. The early embryo is sex- 
ually indifferent and contains all pre- 
cursors and structures necessary for 
the development of either male or fe- 
male organs. After about the eighth 
week following conception, the gonads 
begin to differentiate as either ovaries 
or testes. The developing testes secrete 
androgens, which induce the devel- 
opment of male genitalia. If androgens 
are absent, or present at low levels, 
female genitalia are formed. 
The internal and external genitalia 
develop in different ways. For internal 
genitalia, the early embryo contains 
precursors of both sexes: the Miillerian 
ducts (which form the Fallopian tubes 
and ovaries of females) and the Wolff- 
ian ducts (which form the vas def- 
erens — the ducts that carry sperm 
from the testes to the penis — in 
males). In females, the Wolffian ducts 
degenerate and the MUllerian ducts 
differentiate; males develop by the op- 
posite route. 
The external genitalia follow a 
markedly different pattern. Individ- 
uals do not begin with two distinct 
sets of precursors and then lose one 
while strengthening the other. Rather, 
the different organs of male and fe- 
male develop along diverging routes 
from the same precursor. The male’s 
penis is the same organ as the female’s 
clitoris — -they form from the same tis- 
sues, are indistinguishable in the early 
embryo, and follow different pathways 
later. The male’s scrotum is the same 
organ as the female’s labia majora. 
The two lips simply grow longer, fold 
over and fuse along the midline, form- 
ing the scrotal sac. 
The female course of development 
is, in a sense, biologically intrinsic to 
all mammals. It is the pattern that 
unfolds in the absence of any hormonal 
influence. The male route is a modi- 
fication induced by secretion of an- 
drogens from the developing testes. 
The mystery of male mimicry in 
female hyenas may be solved by rec- 
ognizing these fundamental facts of 
developmental anatomy. We know 
from the work of Racey and Skinner 
that female hyenas maintain high lev- 
els of androgenic hormones. We may 
therefore conclude that the striking 
and complex peculiarities of sexual 
anatomy in female spotted hyenas are 
simply, indeed almost automatically, 
produced by a single, underlying ef- 
fect: the secretion of unusually large 
amounts of androgens by females. 
The automatic nature of peniform 
clitorises and false scrotums in female 
mammals with high androgen levels 
18 
