Researchers investigating calorie restriction have noticed that its effects on longevity can be inherited through epigenetic variations - which makes sense, given the reasons why individual longevity variations in response to available food evolved in the first place. If it is advantageous for a given individual at a given time to shift metabolism into a mode that allows it to live longer due to a decline in available food, then it's probably also advantageous for the children to do that from birth as well: "The tiny soil-dwelling worms C. elegans, when given mutations that make them live longer, transmit that trait even when their progeny don't inherit the life-extending mutations. ... Although much more research remains to be done, the new study raises the tantalizing possibility that if Grandma practiced caloric restriction - which affects the expression of longevity-enhancing genes - her descendants might reap the benefits. The inheritance occurs through "epigenetics": alterations not in the coding sequence of DNA (those ubiquitous A's, T's, C's, and G's) but in chemical changes that affect whether genes are expressed. ... [A] protein complex called ASH-2 [alters] histones in C. elegans, reconfiguring the histone-DNA complex into an 'open' state that promotes gene expression. Deficiencies in ASH-2 extend the worm's life span by as much as 30 percent. ... [researchers] blocked the three key proteins that make up the ASH-2 complex by mutating their genes. As expected, the worms lived longer - typically, an extra seven days beyond their lab life span of 20. [Researchers] bred the mutated worms with normal worms until their descendants no longer had the mutations. Nevertheless, the progeny still lived longer, as did their own descendants: even though their genes for the key proteins were normal, an epigenetic memory of longevity persisted."