Question: when people have twins some people have a sixth sence because they can feel when their other half is feeling, like pain, morning sickness and stuff like that...?

Artem Evdokimov answered on 20 Jun 2012:

It’s hard to differentiate fact from fiction in this area. Alexandre Dumas made ‘twin telepathy’ popular with his 1884 story ‘The Corsican Brothers’. Anecdotal accounts of twin telepathy can be found in various historical documents — but there are no clear, scientifically conducted experiments that demonstrate the effect. I suspect that the effect as it is observed has two parts: one is the expectation of ‘magic’ from twins – because twins are very often considered magical throughout various cultures and ages, so the stereotype is pretty strong. On the other hand we have the good likelihood that twins have similar patterns of thought and behavior so they have (perhaps?) a higher than average chance to anticipate each others’ actions. Note that society generally pays attention to interesting events – such as a twin saving another twin from drowning via ‘telepathy’ but does not recall most of the occasions when in the same situation the other twin drowns. So it’s a very fertile ground for perception bias, I think…

Still, this would be a nice area to have a properly conducted study, and I suspect there were a few out there but I couldn’t find enough to mention here.