Lonely Mitochondria

Sometimes, in the middle of the night, I worry about the endosymbiotic hypothesis of mitochondria. It keeps me awake.

Without mitochondria, the chemical reactions within cells that make multi-cellular life possible would not exist. The endosymbiotic hypothesis puts forward the idea that mitochondria were once individual cells living separately, that were somehow ingested or parasitized by other cells, yet survived, reproduced in their new environment, and provided a great source of energy for their hosts.

If this hypothesis turns out to be true, then here on Earth we have mitochondria by accident -- an incredibly lucky accident. How often could this accident (or any similar endosymbiosis) be repeated on other planets? How many planets are full of thriving bacteria, but with no multi-cellular forms?

Given the sheer size of the universe and the likely number of planets, this lucky accident might have occured many times, but on worlds far apart from each other, so far apart that interstellar contact would be impossible within the lifetime of any civilization, or of any species.

Either way, the implication here is that we live in a universe of planets bulging with life, but not with multi-cellular, intelligent life. And this idea nags at me: we might be alone, or so isolated by chance and by distance, that we will never learn if anyone else is out there. We will never know.