In my mind, there are few sins so egregious as extending life without health. This is important. It does not matter if we can extend lifespans if we … - David A. Sinclair

When the Sir2 enzyme is sitting on the mating-type genes, they remain silent and the cell continues to mate and reproduce. But when a DNA break occurs, Sir2 is recruited to the break to remove the acetyl tags from the histones at the DNA break. This bundles up the histones to prevent the frayed DNA from being chewed back and to help recruit other repair proteins. Once the DNA repair is complete, most of the Sir2 protein goes back to the mating-type genes to silence them and restore fertility. That is, unless there is another emergency, such as the massive genome instability that occurs when ERCs accumulate in the nucleoli of old yeast cells.

After our species was almost driven to extinction 74,000 years ago, up until 1900, the human population grew at a rate amounting to a fraction of a percent each year as we expanded to all habitable regions on the planet, breeding with at least two other human species or subspecies. By 1930, thanks to sanitation and decreases in child-mother mortality, our species was increasing its numbers at 1 percent each year. And by 1970, due to immunization and improvements in food production globally, the rate was 2 percent each year. Two percent might not seem like a lot, but it added up fast. It took more than 120 years for our population to move from 1 billion to 2 billion, but after reaching that mark in 1927, it took just thirty-three more years to add another billion and then fourteen years to add another. This is how, at the end of the second decade of the twenty-first century, we came to have more than 7.7 billion people on our planet, and every year one additional person per square kilometer.

1800, the global literacy rate was 12 percent, by 1900 it was 21 percent, and today it's 85 percent.