Concealed Ovulation As A Side Effect of Bipedalism
Pawlowski presents the importance of bipedalism to the mechanics and necessity of ovulation signaling. The more-open savannah environment inhabited by early humans (as made available by bipedalism) brought greater danger from predators. This would have caused humans to live in more-dense groups, and, in such a scenario, the long-distance sexual signaling provided by female genital swellings would have lost its function. Concealed ovulation is thus argued to be a loss of function evolutionary change rather than an adaptation. Thermoregulatory systems were also modified in humans with the move to the savannah to conserve water. It is thought that female genital swellings would have incurred added cost because of ineffective evaporation of water from the area. Pawlowski continues by saying the change to bipedalism in early hominins changed both the position of female genitals and the line of vision of males. Since males could no longer constantly see the female genitals, swelling of them during estrus as a mode of signaling would have become useless. Also, anogenital swelling at each ovulatory period may have interfered with the mechanics of bipedal locomotion, and selection may have favored females who were less hindered by this occurrence. This hypothesis ultimately concludes that bipedalism, which was strongly selected for, caused the physiological changes and a loss of function of sexual signaling through female genital swelling, leading to the concealed ovulation we now observe.
Pawlowski’s paper offers views that differ from the other hypotheses regarding concealed ovulation in that it pinpoints physiological changes in early humans as the cause of concealed ovulation rather than social or behavioral ones. One of the strengths of this is derived from the other hypotheses’ weaknesses – it is difficult to track the evolution of a behavior as it leaves no verifiable evidence in the form of bone or DNA. However, the fact that the Hanuman langurs also display some concealed ovulation and that it is not directly caused by a physiological change to bipedalism may suggest bipedalism was not, at least, the sole cause of concealed ovulation in humans. As stated earlier, it is possible for many elements of different hypotheses to be true regarding the selective pressures for concealed ovulation in humans.
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