Externalities across monozygotic twins

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.



I'd be pissed that my twin's going to be a free rider when I pay for genetic disease screening.

libert, Don't take anything I said personally. Just making a point about the trouble politicians, more than others, get stuck with the sins of their children or siblings.

And, of course, people do influence the behaviour of their children.

But, sometimes its fun to point out that it is not just mono-zygotics who have relationship problems.

What about your mom?

I wonder to what degree identical twins see themselves as individuals in the typical sense.

To answer Randal Parker's question in a Coasean way, it doesn't matter who has the right (from an efficiency standpoint). What is more important is that someone does have a legally defined right.

I would think that most twins have low bargaining costs (many even have their own language!), so if it means a lot to one twin not to publish his or her DNA, then there will be a side payment of some sort to buy that right.

Because of low transaction costs among twins, my guess is that most all externalities, positive and negative, are resolved with some sort of side payment (although not necessarily with money).


I don't think people infer characteristics of a person from their family based on genetics. I think they infer it based on family history, or "nurture," or whatever you want to call it.

People say "your kid's behavior reflects on you" because your kid's behavior is a function of the example that you set for them when they were growing up.

I've often thought about Tyler's question of what works best for identical twins: acting more or less similar. I don't have an answer, but I've collected a bunch of examples in a column I wrote for Taki's Magazine about what can be learned from celebrity twins:

For example,

"Identical twin stars seem less common in movies than in team sports, where their superior cooperation skills can help. For instance, the Sedin twins of the Vancouver Canucks finished second and third in the National Hockey League in points per game this year. In basketball, tall twins grow up with the advantage of having to pick on somebody their own size when practicing in the driveway. Dick and Tom Van Arsdale, 1970s NBA all-stars, epitomized one trait often seen among identical twins: phenomenal levels of sibling rivalry combined with tremendous loyalty to each other against the world."

That article on swimsuits is either very autistic or very obtuse in not understanding objectification.

Except that identical twins really do tend to be amazingly similar.

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