I actually remember reading a study recently that says that there is some, though hardly conclusive, evidence that humans are biologically immortal. If you don't know what that means, it's basically that once an organism gets to a certain age, it stops biologically aging. Now while things such as disease and trauma can still cause death, aging alone cannot. The effect has been observed in single celled organisms and some larger creatures, but the fact that humans might be is quite incredible. For those that will inevitably ask for a source on this information (and so you should), here it is: Late Life: A New Frontier for Physiology