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ANT 2301 (23)

Parental Investment

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ANT 2301
Geoffrey Thomas

ANT NOTES 10-15  PARENTAL INVESTMENT o Females- 9 month minimum investment to produce offspring  2-3 years lactation  energy- production of age o Males: time… minutes  Energy- teaspoons of fluid o Trivers- “any investment by the parent in an individual offspring that increases the offspring’s chance of surviving at the cost of the parent’s ability to invest in other offspring o Trade-off’s  Time and energy invested in 1 offspring  More care required = greater parental investment = fewer offspring > lower RS  Less care required= less parental investment = more offspring > higher RS o What counts?  Production of sex cells  Internal fertilization  Gestation period  Placentation  Lactation period  Send off to college  Many dependent on females o Birds- external care means both sexes can invest o Mammals> humans> internal care> only females  Reproductive rates o Sex. Interest and receptivity to sexual offers should differ b/tween males and females  Males should be more easily aroused after mating  Males should be more receptive to sexual offers  Coolidge effect: males are often re-aroused by the sight of a novel female o Contrast effects  Kenrick examined the effects of exposure to attractive nude females on male sexual attraction judgments  16 pictures of nude females or 16 art slides  Males exposed to attractive female showed significant reduction in ratings for their partner  Clark and Hatfield  3 invitations o 50% would go on date- 70% go to apartment- 75% go have sex o 50% would go on date- 10% go to apt. -1% go have sex o Risk of investment  Woodward’s and Richards  In presence of real risk of investment, female and male choosiness converges and increases over than a one- night stand  Altruism and Kin Selection o Altruism  Refers to an individual acting in a way that will decrease its own survival chances, but improve the survival chances of another individual  Natural selection seems to favor selfish behavior  Examples:  Ground squirrels warn others of predator but is now the center of attention to that predator  Bees will forgo reproduction entirely in order to help raise sisters  Vampire bats will regurgitate blood that they have collected to feed a hungry relative  Theories:  Kin selection: (Hamilton 1964) o By helping relatives to reproduce (even at your own cost) then your shared genes can spread. Assisting a close relative thereby increases one’s ‘Inclusive Fitness’ o ‘Hamilton’s Rule’= rB >c  R = coefficient of relatedness, B= benefit to the recipient, c = cost to the giver  Barrett (2002) – found to be trait of human society o Food sharing is more common amongst close relatives o Political alliances between kin are more stable than those formed o Close relatives are preferentially sought out in times of need and such help is less likely to be reciprocal o How much pain? More pain was sustained for closer relatives  Problems for kin selection: o Donate blood o Adopt unrelated children o Donating to charity o Forgoing reproduction o Rescuing unrelated individual o Sacrificing their lives for moral or ethical principles o Reciprocal altruism  Proposed by Trivers (1971)  ‘You scratch my back…’  if the benefit received is larger than the cost incurred, then individuals who engage in such behavior will out- reproduce those who don’t  in vampire bats: a bat will share food with a friend who has shared food with that individual in the past o Indirect reciprocation  Trivers argued that an altruistic act need not necessarily be reciprocated by the person directly assisted but can be returned indirectly from others  Giving blood: don’t know who you helped but you get a sticker for it  Evidence  Reported students are significantly more likely to give charity if they receive a pin or tag that advertises their participation (Low and Heinen)  Observed who gave to beggars and mixed sex couples after the male donated money (Mulcahy) o
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