And because aging isn't a disease by the commonly accepted definition, it doesn't fit nicely into the system we've built for funding medical research… - David A. Sinclair

After a few billion years of advancement since the days of yeast, they have evolved to control our health, our fitness, and our very survival. They have also evolved to require a molecule called nicotinamide adenine dinucleotide, or NAD. As we will see later, the loss of NAD as we age, and the resulting decline in sirtuin activity, is thought to be a primary reason our bodies develop diseases when we are old but not when we are young.

Death by death, the world sheds ideas that need to be shed. Ipso facto, birth by birth, the world is offered an opportunity to do things better.

When sirtuins shift from their typical priorities to engage in DNA repair, their epigenetic function at home ends for a bit. Then, when the damage is fixed and they head back to home base, they get back to doing what they usually do: controlling genes and making sure the cell retains its identity and optimal function.