Two hundred years ago, no country on earth could expect its population to live past 40. Today, the average life expectancy is about 72 worldwide. Medical and technological developments — like the discovery of germs and the development of vaccines and antibiotics — have made it possible to live longer, healthier lives. Scientists estimate the maximum human life span may be about 120 years.

So why, even in developed countries, do most of us only make it two-thirds of the way there? What is it about old age that makes us so susceptible to disease, injury, and death? If we figure that out, could we live forever — and would we even want to?

Vox tackled these questions on this week’s episode of our Netflix show, Explained. We have new episodes every Wednesday on topics ranging from gene editing to dieting to weed and more. If you like our videos, then you’ll love this show; it’s our most ambitious video project to date.

To watch, search “Explained” on Netflix or go to Netflix.com/explained. Click the “My List” button to make sure you don’t miss an episode.

Learn more:

The Men Who Want to Live Forever (Dara Horn, New York Times)

Seeking eternal life, Silicon Valley is solving for death (W. Harry Fortuna, Quartz)

Elder care costs deplete savings of a generation (Jane Gross, New York Times)

Can we grow older without getting sicker? (a TED talk by researcher Nir Barzilai, whom we interviewed for this episode)

Experiments that hint of longer lives (a TED talk by Cynthia Kenyon, whom we also interviewed for this episode)

Why I hope to die at 75 (An essay by medical ethicist Ezekiel J. Emanuel, whom we also interviewed for this episode)

What were we thinking? (Philosophy professor Kwame Anthony Appiah, whom we also interviewed for this episode, has some choice words about, among other things, the way we treat older adults)

This 23-year-old wunderkind seeks a new age for old age (a profile of aging biotech engineer Laura Deming, also interviewed)

BioAge Labs raises $10.9M in Series A financing to accelerate drug discovery for aging (an essay by BioAge CEO Kristen Fortney, also interviewed)