Sexual Selection

  • Darwin noticed that there were certain features that he could not explain by Natural Selection
  • Such as differences in size, body form, colouration and behaviour between males and female of the same species – why are females often smaller and less colourful than males?
  • Infact, in some species, the male seems at a real disadvantage in that he would show up to predators by being brightly coloured, he might have huge antlers that mean he can hardly lift his head, or he may have a huge tail that would get caught in the undergrowth
  • Why would it make evolutionary sense to have such features that are only going to get you eaten???

Differences in the appearance etc. between males and females of the same species are referred to as SEXUAL DIMORPHISM

Humans are sexually dimorphic to a certain extent with females being generally smaller, less muscular and without features such as facial hair

Sexual Selection (as opposed to Natural Selection) was Darwin’s solution to this problem:

  • He suggested that the differences must be due to an advantage they give in passing genes into the next generation
  • Females are ‘in demand’, so sexual selection will mostly operate on the males who have to work to get access to the females
  • The features will either help the males to compete with other males and ‘fight them off’ for access to the females, or they will make them sexually desirable to the females, so they get access to more mates
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INTRAsexual selection  is when features have been selected by how well they helped to fight of the other males (body size, muscularity, fighting ability, aggression etc.)

INTERsexual selection is when features have been selected by how well they made bearers attractive to the opposite sex (peacock’s tail, fidelity? Kindness/nurturing? Body shape?)

Intra – within own sex

Inter – outter apperance

The human situation is slightly different to that of the other animals due to the need for extended care of children. Males need to stay around to ensure a child is to survive, and so he needs to be more ...

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