[paul.fr]

I know you can age things by carbon dating, but what about DNA?
If we found an old human bone, Would it be possible to date it through the DNA? Say a particular sequence only 'appeared' at a certain stage of evolution, would we be able to identify it and age the bone accordingly?

[chris]

Hello Paul.

Absolutely. In fact, this was precisely how a group of scientists recently calculated the age of the average fat cell in a human body. They used carbon-14 levels from the environment and the point that when a cell is "born" its DNA, containing some radioactive carbon atoms, is fixed inside it. From this point on the carbon in the DNA decays, to nitrogen-14, and is not replaced (by further carbon-14), so the DNA becomes progressively less radioactive.

By comparing the radioactivity levels of DNA from samples of aged fat cells with the radioactivity of newborn fat cells the researchers were able to calculate the average lifespan of a fat cell in the body, overturning a long-standing myth (that fat cells last a lifetime) in the process.

Instead what the researchers found (Spalding et al., Nature May 4th 2008) was that fat cells live about 10 years, and that new cells are continuously being produced to replace those that die. Interestingly, the level of fat cells in adolescence becomes the set-point for the number of fat cells maintained during adulthood.

In other words, fat kids have a preponderance to turn into fat adults. Worse still, dieters can shed fat, but not fat cells. And since fat cells produce hormones linked to hunger, less full fat cells means more hunger pangs and a tendency to eat more...

Chris

[Madidus_Scientia]

So that's why its so hard to lose weight past a certain point, and so easy to bounce back to it. I wonder if there's a way we could trick our beerguts into decreasing the set amount of fat cells. I suppose then we'd have to actually kill a few of them along with it too so we don't have to wait 10 years