You might recall that researchers are making efforts to correlate psychological states, such as character traits and stress, with aging and the biochemistry of aging. Here is another item from that side of the field: researchers "have now shown that sirtuins likely also play a key role in the psychological response to dietary restriction. When sirtuins are elevated in the brain, as occurs when food intake is cut, mice become much more anxious. Furthermore, in two large genetic studies of humans, the team found that mutations that boost production of sirtuins are commonly associated with higher rates of anxiety and panic disorder. The researchers believe that this anxiety may be an evolutionary adaption that makes animals - including humans - more cautious under the stressful condition of having to forage more widely for scarce food. ... It makes sense, because behavior effects would be as adaptive, and as selected by evolution, as physiological effects. I don't think it's surprising that behavior really falls under the umbrella of natural selection." Of course there is uncertainty over whether sirtuins are actually important as drivers of the enhanced longevity produced by calorie restriction.