Youthful Aging Does Not Equal Immortality

I study the genetics of aging in model organisms in the laboratory, which involves identifying genes that are directly responsible for promoting or preventing long life. For example, in the model organism C. elegans, a tiny nematode worm that lives for 2-3 weeks on average, a particular gene can cause the worm’s lifespan to double when the gene is removed from the worm’s genome.

Can this gene also double a human’s lifespan, you might ask? Well, we do have this same gene in our genome (which is why it is relevant to study it in C. elegans in the first place), but we can’t exactly remove the gene from the human genome like we can do in C. elegans. Scientists do know, however, that natural variations in the gene’s DNA sequence do correlate with longer life, in which centenarians have a different variation of this gene compared to non-centenarians. In fact, this particular gene I am referring to codes for a protein that is responsible for receiving signals from the insulin hormone, which is why there is no surprise that centenarians who have a particular variation in the gene also have a lower occurrence of diabetes and obesity.

However, what’s important to note is that the variation in the gene’s sequence results in people living to be 100, not 150, which would be double the average lifespan of Americans. Thus, there are limits as to how we can translate findings obtained in model organisms like C. elegans, and as humans are significantly more complex, we are not accustomed to such drastic changes in evolutionarily-defined limits to our lifespan. Further, who’s to say that C. elegans worms crawling around in the soil in their natural environment would end up living for 6 weeks like laboratory C. elegans worms can?

I might also add that, although these longer-lived worms remain youthful for twice as long, this doesn’t mean that there aren’t any “wrinkles” as a result: in fact, these particular worms that live for 6 weeks have a reduced fecundity. So, there are always trade-offs in nature; if your body is exerting more energy keeping you youthful, then it will exert less energy for other things.

It’s also important to note that by changing the genetics of C. elegans, there is no way to make the worms live forever; after a certain number of weeks, they will eventually all die off. This is why it is important to separate laboratory genetics from the more science-fictiony “elixir of youth.” Save for the “immortal jellyfish,” Turritopsis dohrnii, which, in a Benjamin Button-life fashion, can age in reverse until it reaches the earliest stage of its developmental cycle before starting this cycle again from the beginning, immortality is not part of animal nature.

There are certainly animals that outlive humans, like crustaceans and hard clams, but they still have an expiration date. The immortal jellyfish is also a special case; natural selection has shown that aging in reverse allows the jellyfish to be the most “fit,” perhaps in an attempt to stray from predators. Humans would never need to age in reverse to stay away from predators, which is why we cannot do this ourselves. By studying human aging, it is also quite clear that factors like diet and environment correlate with how long you live and how long you remain youthful. Is it only due to genetics that the Japanese are the longest-lived ethnic group, or is it because of the way Japanese people live? The simple answer is probably that it’s a little of both.

Even though the longest-lived person was 122 (according to Wikipedia), immortality can still be something interesting to envision (maybe this is why vampire shows are so popular??). However, according to a NY Times poll from last year, while it may be fun to think about living forever, very few people would actually want to experience this. By polling 30,000 people, the NY Times concluded that 60% of people wanted to live for 80 years, 30% for 120 years, almost 10% for 150 years, and less than 1% forever. So, if you do want to find that “elixir,” you may be the only one drinking it.

http://www.nytimes.com/2012/08/26/sunday-review/how-long-do-you-want-to-live.html

http://www.nytimes.com/2012/12/02/magazine/can-a-jellyfish-unlock-the-secret-of-immortality.html?pagewanted=all

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