chapter 9.docx

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25 Apr 2012

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The Evolution of Communication Chapter 9 p-287-294
The Origin and Modification of a Signal
In the family of Hyaenidae, including just four species, one being the spotted
hyena, chemical communication is used by all species
Chemical communication involves use of their anal scent glands to mark their
home habitat
Male and female hyenas also inspect the anogenital regions of their companions
and therefore the ancestor of the spotted hyena probably engaged in similar
Females of the immediate predecessor of spotted female hyenas added the
inspection of the erect penises of their fellow hyenas, male and female alike to
their anogenital analysis
In 1939, Harrison Matthews proposed that the pseudopenis might be the
developmental result of high levels of male sex hormones in female hyenas
Stephen Jay Gould introduced this as a hypothesis and stated that the male
penis and female clitoris of mammals develop from exactly the same embryonic
The general mammalian rule seems to be that if these tissues are exposed early
on to male sex hormones (testosterone and other androgens) as they almost
always are in male embryos, a penis is the end result
When a female embryo of most mammals comes in contact with testosterone,
either an experiment or as a result of an accident her clitoris becomes enlarged
and looks like a penis
Gould felt that the female spotted hyenas must be exposed to unusual
concentrations of male androgens
A paper further supported his hypothesis who reported that female spotted
hyenas had circulating levels of testosterone equal to those males, unlike other
hyenas and mammals generally
This confirmed the hypothesis that an unusual hormonal environment led to the
origin of the spotted hyena’s false penis, setting the stage for the origin of the
dual sex penis sniffing greeting ceremony.
Testosterone levels in free living females are actually lower than adult males,
pregnant woman have higher levels of testosterone than lactating woman
Fig 9.2
Males and females have similar levels of a precursor of testosterone called
androstenedione, but the placenta of the pregnant female converts this into
testestosterone, her females embryo could be exposed to high levels of
masculinising testosterone
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