While there is no unified theory about what causes aging in living things, there is speculation. The first theory I’ll cover in this series of posts, Theories of Aging, is the Error Catastrophe Theory.
In the 1960s it was proposed that all the steps cells go through to create proteins for enzymes or structural support, or to divide and replicate, could accumulate errors that would be replicated over and over and eventually cause the cells to age and die.
To test the hypothesis, cells were grown in a medium filled with defective amino acids, sure to cause errors in cells. Fruit flies and mice were also fed damaged amino acids, but to everyone’s surprise, there was no effect on the organism’s health, vigor, or life span. It turns out cells have excellent detection and destruction mechanisms that rid the cell of protein defects or faulty copies of DNA.
This initial failure didn’t kill the hypothesis, however. There is still evidence errors accumulate if the genes themselves are damaged or the repair mechanisms slow or break down. Below are some pros that seem to support the Error Accumulation Theories, but for each pro there is a con.
- PRO-Cataracts are a case of aging by accumulated errors. Crystalline proteins found in the eye are replaced throughout the lifespan, but slowly, and the existing copies are damaged over time, leading to the opacity of the eye’s lenses. If crystalline proteins were replaced more rapidly, cataracts could be avoided. Similarly, researchers believe some symptoms of aging might be avoided if buildup of damaged proteins was eliminated. CON- Not all age changes are associated damaged protiens. Some are associated with hormones, among other things.
- PRO- People with Werner’s syndrome might be ten, but look 70 or 80 years old. It’s thought their cells lack the ability to repair protein synthesis errors. CON- In some instances aging is associated with older cells slowing down the repair or replacement process, but in other cases, aging begins long before the processes falter.
- PRO- Studies of long-lived organisms reveal that more efficient protein repair systems are often associated with longer life spans. CON- Some long-lived species have less efficient repair of damaged proteins, and vice-versa.
There are more theories of aging that I’ll explore in this series, some are less promising than others, but the Error Accumulation theory is promising because all errors occur in all cells at one time or another. It is up the the ever advancing field of gerontology to find out how, and if, the many theories of aging converge.
I’ve been enjoying the blog, and error accumulation makes a lot of sense. I know this may be a bit tangential, but I often wonder how we as humans get “stuck” with a trait in our biological or physiological makeup (such as genetic diseases, mental illness, etc) and why natural selection wouldn’t have weeded out these unpleasant traits. I’m kind of into finding root causes for things.
In the case of aging, whether it’s the cells slowly losing efficiency as errors are incurred over time or a combination of all sorts of things, I’m curious to know how, over the ages, living longer may have effected our (or any animal for that matter) competitive advantage in the natural selection process.
Early man would presumably appear to only live long enough to raise children, and some extra longevity would seem to be a bonus in being able to contribute wisdom to help your family/group/tribe succeed. Perhaps living longer may have negatively impacted the gene pool or diminished the available resources, so, in fact, those individuals who did age and subsequently die, were making room for a more diverse, better-adapted generation. This would better ensure the species survival, which seems counter-intuitive to having a remarkably long lifespan.
Again, maybe the aging thing is so fundamental to life that, right out of the gate, the “primordial soup” had to sacrifice longevity for selectivity through new generations. This “hard-wired” limiter could be very difficult to overcome, much like entropy itself. Obviously this is another topic for another time, but it’s such an interesting angle to me. Thanks for the fun reads Laura!
Thank you. I enjoyed your comment. I am going to discuss a lot of what you mention in future posts. I also find it fascinating.