What do you strongly suspect but have no proof of?

Some people are just robotic shells and don't actually have a "soul". But are instead what are known as a philosophical zombie. But to prove that you'd have to prove a soul even exists to begin with. Then test to see if an individual has one or not.
The closest we have is a person's conscience and some people are shown not to have one and can't feel things like love or empathy. I don't consider those people to actually be alive. Maybe alive the way a virus is alive.