it. It is, in essence, a primordial survival kit that diverts energy to the area of greatest need, fixing what exists in times when the stresses of t… - David A. Sinclair

Our equivalent of the Lord's Prayer was the English author Alan Alexander Milne's poem "Now We Are Six," which ends: But now I am six, I'm as clever as clever. So I think I'll be six now for ever and ever.

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.

What's the upward limit? I don't think there is one. Many of my colleagues agree.14 There is no biological law that says we must age.15 Those who say there is don't know what they're talking about. We're probably still a long way off from a world in which death is a rarity, but we're not far from pushing it ever farther into the future.