Oh I love this conversation  ::) I teach a module on biological aspects of aging and there are a number of prominent theories including:<br/><br/>Cross linkages<br/>Wear and tear<br/>Autoimmune<br/>Free radical<br/>Cellular aging<br/><br/>However, they all focus on AGING - meaning getting older. 1/2 of the crew is also getting younger. I would imagine that we could assume that either directly (somehow altering our basic genetic structure or through hormonal changes) or indirectly (their crap) is affecting our body. Perhaps this is where Trek-science comes into play. What's happening to the crew cannot be explained with current theories on aging so we have to make one up. I personally like the "crap" theory, but if you think about it too much you get grossed out!