Steven Crane Compiled Section Handouts. Human Behavioral Biology 2012

Genetic influences on Sexual Behavior

How do you interpret the twin study research on sexual orientation?

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  Full siblings are only 9% concordant for sexual orientation, so the higher percentages in DZ and MZ twins are probably due to environment (esp fetal environment!).
  
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  And the Hammer studies showing genetic markers?
  

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  Not the same marker in different pairs
  
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  Not replicated
  
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  Poor scientific reputation
  

Evolutionary Influences on Sexual Behavior

Is sex for the purpose of social cohesion and cooperation?

• Probably not. Probably more about reproduction.

• Bonobos as exception.

Sex differences in promiscuity

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  Sperm cost a lot less than pregnancies so females are choosy and males are promiscuous. Most seen in tournament species. Less seen in pair bonding species.
  
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  Males often try to control female reproduction across the animal and human kingdom. In what ways?
  

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  Clitorectomies and chastity belts in nomadic societies
  
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  Males actively decreasing the attractiveness of females to other males.
  
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  Sperm compete with sperm from other males.
  
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  Male domination and linear access models (with exceptions below)
  
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  Also rape
  
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  Also subterfuge
  

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  What female counterstrategies exist?
  

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  Concealed ovulation to trick males
  
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  Pseudo-estrus to trick males (esp in cases of competitive infanticide)
  
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  Female choice. Sneaky sex in the bushes to subvert the linear access model: stolen copulations. They like the nice guys (nice guys FTW!).
  
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  Sperm dumping from males they don't prefer
  

How do we explain the evolution of homosexuality?

• (this is assuming there are genetic influences: see above for why there's probably very few)

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