You probably heard this already, but ...
NPR did a really terrific story about oxytocin, trust and civilization. It started with a little girl with Williams syndrome, something I had not heard of.
According to the Williams Syndrome Foundation, "Individuals with Williams syndrome have a very endearing personality. They have a unique strength in their expressive language skills, and are extremely polite. They are typically unafraid of strangers and show a greater interest in contact with adults than with their peers."
Unfortunately, this is only one of multiple health problems caused by this syndrome.
Although it makes sense that the excessive friendliness and trust are the result of "excess oxytocin," in fact, there are no studies showing that this is the case, or how the oxytocin system is involved.
You can read and listen here: