Some traits are valued more highly by one sex than the other
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
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
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)?
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