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Lecture 18

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Biology 1001A
Tom Haffie

Some traits are valued more highly by one sex than the other  Circulating estrogen  Facial features more “feminine”  Waist to hip ratio  Men are more upset if cheated on sexually, whereas women are more upset about being cheated on emotionally Sexual Selection  Why does it happen?  Relative parental investment  Which sex competes, which chooses?  Lower parental investment always competes for higher parental investment  Can it operate on both sexes at the same time?  Yes, but there are still persistent sex differences Cooperation & Conflict  Self-sacrifice on behalf of another group of organisms Selection is Fundamentally Competitive  There is a struggle for existence  Really competitive process But group living and cooperation are common  i.e. elephants, wolves, fish  Wolves live in social groups, cooperate in hunting Types of social interaction  Actor Benefits & Recipient Benefits: Cooperation  Actor is Harmed, Recipient Benefits: Altruism  Actor Benefits, Recipient is Harmed: Selfishness  Actor is Harmed, Recipient is Harmed: Spite  Extremely rare in nature  Altruism is “a special difficulty which at first appeared to me insuperable, and actually fatal to my whole theory” – Darwin Altruism?  Parental care is not really a type of altruism because the individual is increasing his/her number of genes/alleles in their offspring  Self-sacrifice in a way, but they are getting their genes into their next generation  “Fundamentally Selfish” Behaviour  There is a fitness benefit to the parent  Individuals may risk their own life for someone/something that isn’t related to them  Adult brown squirrels give off a sound to scare away predators from other baby squirrels, even if they aren’t their own children: self-sacrificing behaviour because they are more likely to be caught by the predator after making that sound  White footed bee-eaters?  Some of them help their parents raise more offspring instead of going off and reproducing on their own  How can traits that reduce the fitness (offspring production) be selectively favoured?  Sacrificing individual fitness for the good of the group (so they don’t go extinct)?  No. More to “fitness” than simply producing direct descendants  Personal reproduction = Direct Fitness  There’s more than one way to get copies of your genes to the next generation  Perform behaviours and express traits that increase the ability of your close relatives to reproduce  Relatives share alleles with you  Additional reproduction of your relative
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