Trillions dead for one to live

April 23, 2020

I was reading about Welwitschia this week, a strange plant found in Namibia and Angola. Its strap-like leaves grow slowly but continuously along the desert floor. A single plant can grow to thirty metres in diameter, and they can live for millennia. One site noted that only 0.1% of seeds produced manage to germinate.

Those odds don’t seem too bad to me. The odds against your existence are much higher than that.

It’s not just that your parents could easily not have met, but just the sheer number of gametes between them. I began the calculation, learning in the process that women are born with 1-2 million eggs, most of which are never viable, and that men can produce up to 300 million sperm cells in every mL of semen. Just multiplying those two numbers gives a result that is already in the trillions.

I gave up there when I found that someone else had done it, and made an infographic here. He found that the number was 1 in 400 quadrillion against you, assuming the existence of your parents.

But the same odds were against them too. The numbers reach the truly astronomical when you try to trace back the lineage. And the final number he comes to is 1 in 102,640,000 — which the graphic compares to 1080 estimated number of atoms in the universe.

Everything in nature, I would argue, has faced similar odds against its existence. There is a massive survivorship bias in everything we see. If we see it, then it has persisted.

Over 99% of earth’s species are long-extinct; of the 5-50 billion that have existed, there are about 8.7 million today. That was in 2011; it’s not just dropping quickly but accelerating, and we might be about to lose a million more.

Depending on how you measure it the odds against something’s existence may be much more than trillions. This does not begin with evolution; it begins long before that. I’ll be discussing this issue of bias in future posts.

I'm Bryan Kam. I'm thinking about complexity and selfhood. Please sign up to my newsletter or see more here.