Why do we age? Part 2 of 3: Are we programmed to die?
In my first blog entry (https://www.minds.com/ScienceMan/blog/are-we-programmed-to-age-962695083828350976) I discussed why is it that we age and discussed the "Wear and tear" model of aging. In a short, this first idea is that we age because the components of our body story wearing down like the components of a car - ultimately leading to our demise. One criticism of this idea is that it does not account for the lack of aberration. In other words, some cars from the 1920's still look pristine and new - far exceeding the average life expectancy of other cars. Here is a quick look at the oldest humans:
This picture above shows Jeanne Calment and Jiroemon Kimura, the oldest female and male ever respectively, and Emma Murano who was the oldest female but past away recently. And below is a list of the 20 oldest people ever to live:
For the most part, 120 years seems to be the limit for human aging. If "Wear and Tear" were deciding things - wouldn't we expect a few anomalies (i.e. somebody living to 150 - or 200) just by doing their best to maintain their parts?
The second idea as to why we age is because, in effect, we are programmed to die. Our development certainly seems to be on a clock:
Many aspects seem to fall in the same line of succession. All born by 9 months, walking and talking by 1-4 years, baby teeth fall from 6-12 years. So wouldn't it stand to reason the process of "growing up" just continues? Menopause by 60, the male equivalent of andropause by 70, and ultimately a programmed death between 80-100 years for most everyone. Similarly our tissues also fade away seemingly as if on a clock:
Certainly, the concept of programmed aging/death is enticing. Evolutionary arguments could also be made for it. In a sense, the herd becomes stronger if the young do not have to compete against the old for precious resources. Furthermore, this concept if true would suggest the existence of a molecular pathway - a so-called "aging" gene. The search for the fountain of youth continues but inside our bodies! After all, if such a gene exists, and we can turn it off, youth can be maintained indefinitely!
However, just the like the fountain of youth - such a gene has never been found. Many genes have come close, and knock-out over expression of target genes like Sirtuins, mTOR, Growth Hormone, Klotho, and dozens more have led to organisms like rats, mice, fruit flies, and worms living longer. Yet, not a single gene so far has been found that controls the whole process. Leaving the question if it is programmed - then how?
In my final entry in this blog series I will bring forward my speculation as to why it is we age... setting the stage for future blog entries on how we stop it!
Feel free to drop comments and questions below!
Blog Entry 1: Wear and Tear https://www.minds.com/ScienceMan/blog/are-we-programmed-to-age-962695083828350976