Some animals and many plants can regenerate parts of their physical bodies when they are cut off somehow.  Sea stars, worms some lizards, just to name a few.  Why can't humans?  I'm sure biologists can give chemical reasons why it doesn't happen for us, but is that the only reason?  In my opinion, it isn't.  We know there have been those freak cases when a person grows a third set of teeth.  How are they different from you and me?
    I think the main reason we can't do it is because collectively, we believe we can't.  If the majority of us believed we could grow new teeth, we would.  If most of us accepted as normal that when a finger gets cut off, a new one will grow back, than that would happen also.  If most of us knew without a doubt that a damaged eye would repair itself, than it would.
    Medical research has shown that much of our illnesses are fully or partially psychosomatic.  We believe something is going to make us sick, so it does.  We believe we were bad and deserve to be punished, so we are.  They also have difficulty testing drugs because a placebo often is almost as effective as the real thing at curing illness.  This isn't because the drug is a failure, but rather that people who believe they have received a cure are likely to recover, even if they got sugar pills.  So if our mind can cause illness and cure illness, why can't it
cause regeneration?  The only reason is because very few people believe it is possible.