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No Cap On Life Expectancy?
Samarkind writes "An article over at Science Daily (no registration req'd) talks about the average life expectancy for people going up all over the world by an average of 3 months per year. They also say that the somewhat pervasive idea that people can only live so long just isn't true. The kicker that I got from the article was that the average life expectancy for men is 65... isn't that about when I'll retire?" Remember the life expectancy includes all the people who die at age 2 or 15 or 21. If you make it past 25 or so, you've got good odds to make it to 80.
This is due to demographics more than life expectancy. That is, there are more 60+ year olds because 60 years ago people were having more children. Indeed, the number of seniors is bound to increase because of demographics. The boomers are aging, and this is going to create a population such that the majority of people will be older folks.
-- This sig is.
First off, some background information. If you take a normal cell, it won't live forever. However, a cancer cell will, provided it is fed. Cancer cells are mutated so they don't respond to feedback mechanisms from other cells, but their most important feature is in their replication.
Does anyone remember early versions of napster? Due to bugs, it wouldn't transmit the last few bytes of every file. For an mp3 file, that meant the mp3 info tag might be missing, or the last few seconds. But what if the copies kept getting resent? Every time, the file would get progresively shorter, and eventually, you'd notice it.
The same thing happens in cells. Due to the DNA replication method, the last few base pairs at the end of the strand aren't duplicated. That's ok, since the ends are basically unused spare buffers. Eventually, the buffer will be used up, and the DNA will get fucked up, and the cell won't be able to duplicate anymore.
Cancer cells have an enzyme called telomerase that adds back to the buffer, allowing it to divide forever.
Of course, there are also other factors that contribute to a finite life span on the cellular level.
There are non-cellular factors to aging as well. For example, collagen (skin) has the cystene amino acid. Cystene contains sulfer, and as you age, the dulfer forms cross links. The result is obvious if you compare geristric skin to newborn skin.
Additionally, the human body is designed for a limited life span. The thymus (important for the immune system) starts atrophying in the late teens, and is useless as your appendix by age 30 or so.
So, while cellular life can be extended, for a complex organism like us, I'd say there is a cap on life expectancy.
Do you even lift?
These aren't the 'roids you're looking for.
In other words we're a long way from reaching the limit to life span - which is important for policy makers and actuaries. But, this does not mean that there is no limit to life span, in the absence of other interventions. In fact, life span has a significant genetic component which has been studied in a lot of different organsms, like fruit files and worms where lifespan is controlled by the daf gene family.
In the worm case, it's not the accumulated insults of living that cause death, instead it's like throwing a switch. Alter the switch and you alter life span without changing quality of life. What causes the daf genes to get activated is still not well understood, but it might relate to the timing of having progeny ... after the worms reproduce they tend to die off, while mutant long lived worms tend to put off reproduction. Here are some labs working in aging research)