It is circular but still correct! There are many situations where there are feedback loops like this: For example: Male peacocks grow large tails because this

It is circular but still correct! There are many situations where there are feedback loops like this: For example: Male peacocks grow large tails because this is attractive to peahen mates. It's attractive to peahen mates because their male offspring are also likely to have big tails, which will lead to better reproductive success because they are attractive to peahen mates.... and so on. So a gene that favours big tails will make more copies of itself in the peacock population than some allele that favours smaller tails, even though from a "design" point of view the smaller tail makes more sense (not as heavy to carry around, means you can run fast to avoid getting eaten etc.) There are many equilibria like this: - the bank is going to go bust because everyone wants to take their money out because it looks like the bank is going to go bust... - the credit card company declines your application because you were declined from getting a credit card by another credit card company. - The company doesn't take you in for interview because you've been out of work for 6 months. They'd rather go after someone that already has a job. In all of these cases, although the outcome is often not optimal (e.g. nobody wants the bank to go bust), and often not fair, the individuals making the decisions are behaving perfectly rationally.