Steven Crane Compiled Section Handouts. Human Behavioral Biology 2012

Recognizing Relatives

Why is it important to recognize relatives? 4 things

• Expressing parental behavior like nursing or paternal investment. Kin selection relies on kin recognition.

• To detect defectors! Like recognizing when some other bird has left you with her eggs, or some other slime mold strain is taking over the fruiting body.

• Mating choices - 3rd cousins all the way!

• Cooperation and aggression

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  Example: Dominance hierarchies in baboons (this is also evidence for vocal recognition of other family lines in baboons)
  

In what ways do species recognize relatives?

• Cell-cell recognition.

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  Like in social bacteria using a distinctive surface protein
  
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  Like in cooperating sperm who swim faster when clumped together. No clumping with foreign sperm!
  

• Innate recognition

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  This is an instinctual, innate system. Note: cross-fostering isn't going to work here. You can't fool innate recognition!
  
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  Like rodents who prefer the smell of siblings that they've never met. Can also recognize degree of ^{relatedness instinctively. Requires what hormones on board?} vasopressin and oxytocin.
  
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  How does it happen? Olfaction and pheromones. Requires oxytocin and vasopressin on board to do this recognition or else you have social amnosia.
  
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  ^{What are in these pheromones that distinguish self from non-self?} MHC proteins. The more distantly you're related to somebody, the more different your MHC proteins are.
  
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  Facilitated by neurogenesis in the olfactory system during pregnancy in rat mothers, as a result of high prolactin levels.
  

• Imprinting on a sensory cue

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  When mothers recognize infants by imprinting some logical cue. The capacity to do so is innate, but the specific cues that tell them who relatives are come from the environment. Things like:
  
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    Vaginal fluid, amniotic fluid, milk, saliva, scent gland markings, response to mating calls
    
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    And siblings and cousins can use these same traits as second-order cues to kin recognition. Rules like "siblings smell like mom's amniotic fluid" or "cousins are the birds who sing songs somewhat similar to mine"
    

• ^{Or vice versa:} when baby ducklings imprint on the first big moving thing they meet after birth, thereafter treating it like mother

• Cognitive derivation of kinship

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  Not by simple sensory rules, not by cell-cell recognition, not by innate mechanisms.
  
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  It's thought and recognition. Examples:
  
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    If I remember giving birth to this individual, it's my offspring.
    
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    If I spent my childhood with somebody, they're probably a sibling (humans). Shown by kibbutz studies and Taiwanese arranged-marriages-from-childhood.
    
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    Two more:
    

  • Face recognition (appearance similarity) in humans (and sheep!)

  • If I mated with this individual's mother a high proportion of the time she was in estrus, it's probably my offspring so I'll be paternal. Higher primates and sunfish can similarly do this.

• In humans

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  We have a special structure, the fusiform "face area" of the cortex in the brain recognizes faces.
  
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  In what disease does the fusiform area not function in a typical manner?
  

  • Autism. Just as likely to light up for a picture of unknown vs. familiar faces.

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  We have elaborate cognitive understandings of relatedness.
  
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  We don't do instinctual smell recognition, but mothers and babies learn each other's smells soon after birth (fathers don't).
  
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  Infants can learn mom's voice in utero (imprinting on a sensory cue)
  
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  Since it's so fluid and subject to error and cognitive, we can have both pseudo-kinship (bands of brothers in the army) and pseudo-speciation (making others seem so non-related as to be of a different species entirely)
  
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  In what 3 ways have we seen humans "fooled" into thinking people are relatives who are not, or vice versa?
  
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    Kibbutz studies and Taiwanese traditional marriages
    
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    German brother-sister couple example: it can't be innate or they would have figured it out earlier!