American mountain sheep are neotenic or paedogenic, depending on their sex. The rams have a juvenile (neotenic) period lasting 5 to 6 years after sexual maturation, during which they develop physically and mature behaviorally. Rams almost double in body weight after sexual maturation, increase their horn mass, grow darker in color, and lose the white fur on belly and legs, grow less gregarious, become more polished in the social behavior by increasing display patterns and reducing aggressive and sexual patterns, and act more "brave" with age. They reach ultimate development and maturation between 7 and 9 years of age. Females are paedogenic since they remain frozen in development at the level of sexually mature yearling rams. Females possess two behavioral states: in estrus they act like young males, but in anestrus they act like sexually immature sheep. Sheep attain strong sexual dimorphism as a consequence of the postpuberal growth of males. The slow behavioral maturation of rams, which is paralleled by physical development, suggests that the quantitative expression of social behavior is a factor of the rams' physical development; the quantitative similarities in behavior between young rams and estrous females suggest that this view is valid.
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Valerius Geist (1968) studied this question.