This observation is completely consistent with the findings in the experimental models [11, 32]. Male levels of testosterone directly induce the growth of the genitalsand indirectly via dihydrotestosterone DHT the prostate.
It is therefore proposed that gynecomastia probably results from failure of adequate testosterone action on the breast primordia during embryonic differentiation. National University of Singapore.
Williams Textbook of Endocrinology E-Book. Cengage Learning. Sexual differentiation begins during gestationwhen the gonads are formed. Ronald Fisherthe English biologist developed a number of ideas concerning secondary characteristics in his book The Genetical Theory of Natural Selectionincluding the concept of Fisherian runaway which postulates that the desire for a characteristic in females combined with that characteristic in males can create a positive feedback loop or runaway where the feature becomes hugely amplified.
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Sexual differentiation begins during gestationwhen the gonads are formed. Hidden categories: Harv and Sfn no-target errors Webarchive template wayback links All articles with unsourced statements Articles with unsourced statements from October Secondary sex characteristics include, for example, the manes of male lions the bright facial and rump coloration of male mandrillsand horns in many goats and antelopes.
Characteristics due to mate choice, often referred to as ornamentsinclude brighter plumagecoloration, and other features that have no immediate purpose for survival or combat. Download as PDF Printable version. Secondary sexual characteristics appear during puberty.
The handicap principle extends this idea, stating that a peacock 's tail, for instance, displays fitness by being a useless impediment that is very hard to fake.
Secondary sexual characteristics emerge at puberty such as low voices and beards in human males, and high voices and no facial hair in human females. Estradiol and other hormones cause breasts to develop in females. In the sexy sons hypothesis, the female chooses the flashy male because his ornamentation will be passed to her sons, thereby giving her sons a greater chance of reproducing and perpetuating her genes.