ANT 2301 Exam 2 Study Guide 5 Concealed Ovulation Lecture Notes Why did concealed ovulation evolve in human species Primate traits Hominin traits o Biomechanics o Behavior and social organization o Visual indicators o Olfactory indicators Modern human traits Terminology Concealed Ovulation o The exact timing of female ovulation able to get pregnant is unknown to both the male and female of a species o Humans are said to have Concealed Ovulation Estrus o Is marked by increases in female sexual behavior proceptivity and attractiveness at the period of highest fertility just before ovulation Haselton and Gildersleeve 2011 o Period of pronounced genital swelling o In Heat Estrus in Humans is highly debated Includes behavioral and physical changes Estrus in Primates Receptivity Proceptivity Attractiveness Receptivity Readiness to copulate when solicited by a male o Pawlowski 1999 No difference in receptivity between humans and primates The younger males with higher levels of testosterone constantly solicit females even without signs of estrus Similar to humans in that there is more of a constant receptivity Proceptivity Active encouragement and solicitations by females to copulate o This behavior is more limited in primates to times during estrus o Proceptive actions peak during periovulatory period of maximum swelling Attractiveness Females become sexually exciting to males o During estrus males find females sexually attractive thus initiating copulations o Most of the female primate menstrual cycle is characterized by sexual disinterest from males o Until estrus Evolution of Concealed Ovulation Primates o Most primates show dramatic increase in mating during estrus period 94 96 Stassmann o The genital swellings are visual in nature and attract males o Changes in hormone levels may also play a role in olfactory attraction and proceptive behaviors in females o The timing of ovulation in obvious so why waist energy with sex when not able to conceive Concealed Estrus Sex Humans Hominins Hominin Estrus Pawlowski o Concealed ovulation from both sexes o Constant sexual receptivity proceptivity and attractiveness o Brief period of fertility during mid menstrual cycle o No estrus swellings but shifts in behavior o What happened during hominin evolution to facilitate these characteristics o Believes that the chimp estrus is an extreme example among primates Evolved after the split with the last common ancestor o More likely the LCA and earliest hominins had a reduced slight genital swelling compared to modern chimps Biomechanical Theory Bipedalism o Centralized foramen magnum o The vertebral column has distinct S curve o The pelvis rotates forward in humans becomes shorter and bowl shaped o The femur angles inward to the knee o The foot develops a distinct arch o Abducted big toe used for toe off walking Biomechanics With increasingly efficient bipedalism o Movement of genitals to underneath the pelvis females o Need a reduction in swelling to maintain biomechanical efficiency Visual Cues By reducing swelling and movement of genitals the visual cue indicating ovulation loss of estrus is no longer advantageous Males cannot see if females are ready to become a pregnant Not in the correct place for signaling Physical indications of swelling Human males have unnecessarily large penises o Avg erect penis length of 14 cm o Avg vaginal depth of 10 12 cm o If at one time hominins had slight vaginal swellings to indicate ovulation o Makes up for the difference in size Or maybe its sexual selection female choice Olfactory Cues Hair loss in hominins Adaptation for heat loss sweating o Hair hold onto smells armpit pubic area o Can you smell someone s pubic area when standing Armpit is closer to nose Does modern hygiene affect our olfactory abilities Olfactory Cues One of the arguments against loss of estrus is odor preferences o Males more often prefer a females odor during ovulation When not on contraception Female Body Odor Signg and Bronstad 2001 o Males smelled female shirts from different times of their cycle no contraception o 3 nights during Follicular phase ovulating and Luteal phase non ovulating Males lead to believe one t shirt worn by attractive female other by unattractive Rated most attractive or sexy smell during Follicular phase Lap dancer Tips o Solid line represents females not on contraception o Dashed line represents females on contraception o Often contraception removes any indications Cues to Estrus in Women Women respond more favorably to flirtation offers to dance when in fertile phase Gueguen 2009 Full body photos taken of women in fertile and non fertile phases were rated o High fertility photo rated as trying to look attractive Haselton et al 2007 High fertility women s party outfits rated as sexier more revealing Durante et al 2008 Auditory Cues to estrus Bryant and Haselton 2009 Recorded women saying Hi I m a student at UCLA o During fertile and non fertile phases of cycle Acoustic analaysis showed higher pitch during fertile phases Fertile phase recording rated as being more attractive sounding Estrus in Humans The traditional claim is that estrus has been lost in humans o But subtle shifts in behavior preference attitude have lead many researchers to rethink what has occurred in humans That being said o Ovulation is still definitely concealed for humans especially compared to other primate species Behavioral Theories What does constant receptivity proceptivity and attractiveness of humans do to the social dynamic Competition Pair bonding Food sharing Paternity Increased paternal care Theory 1 Concealed ovulation reduces male male competition and enhances cooperation among male hunters o Males cannot compete for the females that are ovulating cannot monopolize every o Working together food sharing increases everyone s chances of survival Concealed ovulation enhances bond between man and woman by making woman continuously receptive proceptive and attractive o Males use less energy mating with a single female all the time to insure paternity Male chimps are more likely to share food with females in estrus Concealed estrus may ensure steady food supply o If males do not know when females are ovulating they may provide more food to win female Theory 2 Theory 3 favor Theory 4 o Females may receive food from multiple males Concealed estrus exploits male paranoia over paternity enhances pair bond o Strategy to confuse paternity and prevent infanticide o If male doesn t know when