Overview

Aging is a process we are all familiar with and although we usually think of it in relation to living things, it also applies to more abstract entities such as populations and planets, stars etc. For our purposes we will focus on humans and maybe a few experimental animals.

Life is continuum from birth until death. We can divide it into stages such as youth, middle and old age; indeed different societies may use any number of terms to describe the same process. For uniformity, division into years works best (that is, until the numbers get so large that you would prefer to just use the term ‘mature’).

Now, one might say that John is 55 years old. We all have some notion of what that means. However, someone else might state further that he looks much older than his stated age. And another observer might note that John acts like an adolescent. Hmmm.
What we have done here is define three types of aging: 1) chronological (years), 2) physiological, and 3) psycho-social.

The physiological processes of aging start to become more visible at about age 30. It is interesting to note that when you look at a young population there are much fewer differences between individuals than you will observe in an older group. Genes and environment play a profound role in how we age. We have no control over our genetic make up and initially no control over where we are born and into which socio economic class. Thereafter, however, we are faced with an infinite number of daily choices. For instance:
Should I drink alcohol?
Should I use drugs?
Which kind?
Do I exercise?
Do I overeat?
Should I smoke?
Should I engage in unsafe sex?
Should I get married?
Have children?

The list goes on and by now you can see that at age 55 years John is the product of many choices; some wise and some not so smart. Each having an effect on how aging will progress and how some of the genes will manifest themselves.

Next time we will examine aging at the cellular level.