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ANT 2301 (23)

Concealed Ovulation

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ANT 2301
Geoffrey Thomas

ANT NOTES 09- 24  Concealed Ovulation o Why did it evolve in humans  Primate traits  Hominin traits  Biomechanics  Behavior and social organization  Visual indicators  Olfactory indicators  Modern human traits o Terminology  Concealed ovulation  Exact timing of female ovulation is unknown to both the male and female of a specie  Humans said to have this  Estrus  Marked by increases in female sex. Behavior and attractiveness as the period of highest fertility just before ovulation  Genital swelling  “In heat”  In humans is highly debated o Estrus in primates  Includes behavioral and physical changes  Receptivity  Readiness to copulate when solicited by a male  Pawlowski o No difference in receptivity b/tween humans and primates o Younger males w/ higher levels on testosterone constantly solicit females o Similar to humans in that there is more of a constant receptivity  Proceptivity  Female actively engaging in solicitations by females to copulate o Behavior more limited in primates to times during estrus o Proceptive actions peak during periovulatory period of max. Swelling  Attractiveness  Become sex. Exciting to males o During estrus males find females sex. Attractive, > initiating copulations o Most female primate menstrual cycle is characterized by sex. Disinterest from males o Until estrus o Evolution of concealed ovulation  Primates  Most show dramatic increase in mating during estrus period  94-96%  Genital swelling are visual in nature and attract males  Changes in hormone levels may also pay role in olfactory attraction and Proceptive behaviors in females  Timing of ovulation is obvious, why waste energy w/ sex when not able to conceive o Concealed estrus, sex  Humans:  Concealed ovulation- from both sexes?  Constant sexual receptivity, proceptivity, and attractiveness  Brief period of fertility during mid-menstrual cycle  No estrus swelling, but shifts in behavior  Hominins  What happened during hominin evolution to facilitate these characteristics  Estrus o Pawlowski  Believes that chimp estrus is an extreme ex. Among primates  Evolved after the split w/ the last common ancestor  More likely earliest hominins had a reduced genital swelling compared to modern chimps  Biomechanical theory  Bipedalism o Centralized foramen magnum o The vertebral column has distinct S-curve o Pelvis rotates forward in humans, becomes shorter and bowl shaped o Femur angles inward to the knee o Foot develops a distinct arch o Abducted big toe, used for toe off walking  Biomechanics o Increasingly efficient bipedalism  Movement of genitals to underneath the pelvis  Need reduction on swelling to maintain biomechanical efficiency  Visual cues o By reducing swelling and movement of genitals, the visual cue indicating ovulation (loss of estrus) is no longer advantageous o Males cant see if females are ready to get pregnant o Not in correct place for signaling o Physical indications of swelling  Human males have unnecessarily large penises  Avg. erect penis length of 14 cm  Avg. vaginal depth of 10-12 cm  If swelling- ma
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