chapter 9.docx

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Department
Biological Sciences
Course
BIOC54H3
Professor
Kamini Persaud
Semester
Winter

Description
The Evolution of Communication Chapter 9 p287294 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 speciesChemical communication involves use of their anal scent glands to mark their home habitatMale and female hyenas also inspect the anogenital regions of their companions and therefore the ancestor of the spotted hyena probably engaged in similar behaviour 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 analysisIn 1939 Harrison Matthews proposed that the pseudopenis might be the developmental result of high levels of male sex hormones in female hyenasStephen Jay Gould introduced this as a hypothesis and stated that the male penis and female clitoris of mammals develop from exactly the same embryonic tissuesThe 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 androgensA 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 hyenas 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 womanFig 92 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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