Suppose you have a right to genetic privacy. You might believe you do. Suppose you have an identical twin. Suppose the identical twin decides to publish his (or her) genetic sequence on the web. Do you have the right to stop this?
That is from Randall Parker. More generally, how much do identical twins impose Pareto-relevant externalities on each other?
One model is that each twin benefits the other by finding an appropriate niche and pursuing some degree of differentiation. In this view, too much "sameness" is bad for each twin. I believe that is the common intuition, and it suggests that twins will in effect pay each other to be more different. It also suggests that the resulting behavior of each twin is not quite at that twin's ideal point; if not for the deal each twin would prefer to be less different.
An alternative model is that a "doubled" person is more than twice as productive as a singleton. For instance, positive reputation earned by one twin rebounds to the benefit of the other. Just as companies and brands and families carry and spread reputations across collectives, so might signals of a common zygote. If twins can signal that they are quite similar, perhaps more overall trust (or mistrust?) will be produced. On these grounds, might twins implicitly subsidize each other's transportation into public spaces, to parties, and so on?
How much more easily can identical twins trade with each other?
Katja has a related post on women and swimsuits.