  As the quotation from Arrow (above) suggests, there is a puzzle about why permitting payment for blood or organs should be thought to reduce the amount of altruism in the world. For why couldn't paid and unpaid donation systems peacefully coexist, with people who want to give freely continuing to do so? Furthermore, paid donations may even add to the amount of altruism in the world. For there can be cases in which a person sells an organ not for ‘selfish’ reasons, but in order to pay (for example) for someone else's medical care (Brecher 1994).