The problem with any cooperative system is that there are those who try to get more out of it than they put in. The whole system will collapse if we don’t put a halt to freeloading, which is why humans are naturally cautious when they deal with others.
That's from Frans De Waal's The Age of Empathy. The message is that a healthy bit of skepticism of others is necessary to punish freeloaders and keep society functioning. More interesting to me was his description of what happens when people are not discriminating of others. It turns out there is a rare condition that causes people to be extremely friendly, trusting, and likeable, but despite these characteristics, people with this condition are unattractive as friends because in-group loyalty requires out-group discrimination. At least that's my take. Here is Fran's version, slightly trimmed:
Strange things happen if this caution is lacking. A tiny proportion of humans is born with a genetic defect that makes them open and trusting to anyone. These are patients with Williams syndrome, a condition caused by the nonexpression of a relatively small number of genes on the seventh chromosome. Williams syndrome patients are infectiously friendly, highly gregarious, and incredibly verbose.
Even though it is hard to resist these charming children, they lack friends. The reason is that they trust everyone indiscriminately and love the whole world equally. We withdraw from such people since we don’t know whether we can count on them. Will they be grateful for received favors, will they support us if we get into a fight, will they help us achieve our goals? Probably none of the above, which means that they don’t have anything that we’re looking for in a friend.
Williams syndrome is an unfortunate experiment of nature that shows that just being friendly and trusting is not sufficient for lasting ties: We expect people to be discriminating. That a small number of genes can cause such a deficit tells us that the normal tendency to be circumspect is inborn. Our species carefully chooses between trust and distrust, as do many other species.
