Don't be disheartened by my claim that we are the biological equivalent of an old DVD player. This is actually good news. If Szilard had turned out t… - 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.

The other pathway is a metabolic control enzyme known as AMPK, which evolved to respond to low energy levels. It has also been highly conserved among species and, as with sirtuins and TOR, we have learned a lot about how to control it.

We'd die quite quickly without amino acids, the organic compounds that serve as the building blocks for every protein in the human body. Without them — and in particular the nine essential amino acids that our bodies cannot make on their own — our cells can't assemble the life-giving enzymes needed for life.