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sexual selection, The Logical Hurdle: Fisher's hypothesis relies on a…

- - - - Why the sexes differ so drastically in many species, and why the male is typically the more elaborate sex
    - - How traits other than reproductive organs (e.g. a peacock’s tail) = secondary sexual characters can evolve even if they make survival harder.
- - - - Males: Best increase success by securing copulations with multiple partners
      - Females: Best increase success by converting environmental resources into high-quality eggs and offspring
  - - - Optimal reproductive strategies diverge
        
        Males: Maximize fitness by fertilizing as many females as possible
        
        Females: Maximize fitness by being highly "choosy" about the quality of their mates
- - - - heritable benefits
        
        Fisherian Runaway Hypothesis ("Good Taste")
        
        the genetic mechanism
        
        An association between a male trait (e.g., tail length) and a female preference becomes fixed in a population
        
        Offspring inherit genes for both the trait (from father) and the preference (from mother)
        
        They express only the character appropriate for their sex
        
        Handicap Hypothesis ("Good Genes")
        
        the genetic mechanism
        
        Because they are costly, they act as honest signals of a male's underlying genetic quality
        
        Only high-quality (fit) males can survive while carrying these handicaps
        
        Extravagant male traits are physically and energetically costly "handicaps"
      - direct benefits
        
        Females choose male traits that directly increase offspring or maternal survival (e.g., food, protective territories, paternal care)
- - - - The Scent Rule: The more varied an individual's MHC genes, the stronger their immune system
        
        Partners with different MHC genes produce offspring with superior survival chances
  - - - Animal sensory systems differ
        . For example, reptiles, birds, and some insects can see in the ultraviolet (UV) spectrum
        .
        
        Example (Ostriches): White feathers signal offspring growth rate and are especially visible to ostriches because they match their visual spectrum.