Aging ≠ Entropy

In an interview with the NYT, Sean Carroll noted that entropy and aging are related. Jerry Coyne complicates that equation:

There are several theories of ageing.   The evolutionary “pleiotropy” theory says that it pays organisms to reproduce earlier rather than later, so genes that enhance early reproduction even if they cause later problems such as tissue senescence will often be favored.  There’s also a “physical breakdown” theory: the thousand natural shocks that flesh (or stem) is heir to will eventually wear out an organism so that it simply ceases to be.  A variant of this is the mutation-accumulation theory, in which mutations simply accumulate in the somatic (i.e., non-reproductive) tissue over time, and bad mutations that have their effects later in life will be less disadvantagous than those whose effects show up in youth.  This could lead to the accumulation of “ageing genes” and hence produce senescence—the physical breakdown of individuals as they age.

There are other theories, too, and they’re nicely summarized in the Wikipedia article on senescence. But I think none of these are solely explained by “the arrow of time” and entropy.  If organisms could simply take energy from the environment (ultimately, of course, derived from the Sun’s increasing entropy), it’s possible to repair mutations (this is already done to some extent) or fix bodily damage and prevent ageing.  Another way is to reproduce by splitting or by nonsexual reproduction (parthenogenesis), which is practiced by many organisms like the rotifers.  Indeed, the fact that an ageing organism can reproduce at all and produce new, non-senescent offspring is evidence against Carroll’s assertion.  Reproduction, sexual or otherwise, shows that it’s not entropy alone that causes ageing, for reproduction completely nullifies the ageing process, and, when an old decrepit soul like me produces a child, the increase in entropy is reversed.

Coyne’s analysis points out the simple fact that lots of animals seem to fend off entropy better than others and, furthermore, that reproduction itself proves biology has developed a way to get around it. Life finds a way.