Re twins. Yes identical twins are not identical in every way, but they are much more alike than non identical twins. And their environment is not identical, they do not have identical experiences. Also there is a tendency among some twins to want to assert their own individuality, so they become more different from eachother consciously and deliberately. All of this would explain why they are not identical in every way. No need postulate another mechanism such astrology to explain the discrepancy.

As for contagious yawning (of course it depends on what level of explanation you are after), I think the most common theory is that it developed as a mechanism for coordinating sleep times within a community. Interestingly individual differences in susceptibility to contagious yawning is related to levels of empathy, and I think that autistic people are much less susceptible to it.

Bagpuss