In the February 2nd, 2010 Deakin Philosophical Society meeting, we discussed the idea that humans may one day no longer age (after watching a TED lecture on the subject by Aubrey de Grey, which can be found here). In the discussion the followed, there seemed to be a disagreement which, in my opinion, hinged on a fundamental misunderstanding on how each party in the discussion was defining the term ‘immortal’; one side (my side, for those of you playing at home) was using a more biological definition of immortality, the other was using what might be the more colloquial sense of the word (namely, never having to die).
My take on the word immortal (at least, my usage of in during this debate) was more in line with biological immortality. The basic, one sentence summary of this concept would be where the death rate of an organism is not affected by the age of the organism. With humans (and animals in general), once adulthood is reached, the probability of an individual dying in the following year increases (that is, the older you are, the more likely you are to die). This graph from the Australian Bureau of Statistics illustrates the idea nicely:
Biological immortality would be represented in a graph like this:
That is, once adulthood was reached, the death rate would remain static (more or less). This is not to say people would not die, just that there would be no correlation between age and death rate. There would still be a correlation between life style choices and death rate (i.e. if you drink and drive, you’d have a higher probability of dying than someone who didn’t drink drive).
In using ‘immortal’ in this sense, I believe it is perfectly acceptable to say that humans will one day become immortal.
It should be noted that there may still be an indirect correlation between age and death rate in a biologically immortal race; it is possible that life would become mind-numbingly boring after many hundreds or thousands of years. Thus, the older people get in a biologically immortal society, the more likely they are to choose death.