Hi,
I thought it would be good to have a thread where we can say things about society we don't understand and people who do understand them can explain it to us. Then the next person will post something they don't understand and so on.
These are the main things confusing me at the moment:
Why do some people always dress in a very revealing way?
Why do people in relationships want to live together - doesn't it get annoying having someone in your face all the time and having your every move, behaviour and word scrutinised?
Why do people have children?
Would appreciate any ideas / answers to help me understand these things. Thanks.
1. Sex. Unfortunately.
2. Sex.
3. Continuation. Sex is an evolutionary compulsion.
Sorry to be succinct and rational about it. 
You are confusing the means and the end. In evolutionary terms, all that matters is having lots of children who grow up and have lots of children. But to have lots of children, and see them off into adulthood safely, you need incentives. That's why we evolved to enjoy sex, but also why there is such a thing as love, and why there are chemical stimuli that incite people to stay together and take care of their kids and have more kids (which they, of course, don't have to to have sex nowadays, with modern prevention methods).
There's nothing particularly rational about reducing it all to sex (even if you put in a smiley!)
Hmmm...have you read The Selfish Gene? Pretty much contravenes all of the above, bar evolving to enjoy sex. Monogamy isn't natural.