The word and concept were coined by American physiologist Walter Cannon in the early 20th Century. The concept is that living things have mechanisms that help them to maintain a steady state – of temperature, chemical composition, etc. – resisting external forces to the extent that those mechanisms are not overwhelmed. Cannon’s work built on the ideas of 19th Century French physiologist Claude Bernard who introduced the idea of the internal milieu – the internal environment of a cell. If you studied the life sciences, you probably ran across Claude Bernard’s ideas.
I read my Morning Brew newsletter this morning and found myself thinking about homeostasis. The opening item in the newsletter was Earth Day, and there was a quote describing the things that favor life on Earth. The concept of homeostasis applies equally well to single cells, plants, animals, ecologies, planets, possibly larger structures such as star systems and maybe even galaxies. I know, it’s a stretch; let’s stop at planets then.
In Sci-Fi there is a recurring theme of planetary defenses. Examples include:
- STOS – an ancient obelisk that housed a deflector beam that protected a planet from errant asteroids
- Babylon 5 – a halo of satellites around Earth that could launch missiles at incoming invaders
- Starship Troopers – an array of Moon-based cannons that could blast incoming Bug Meteorites
- Avengers: Endgame – in which Tony Stark laments that the Earth never got a suit of armor to protect it from alien threats
- and many others
The idea of a planetary defense system isn’t really so fanciful. Earth already has one – albeit imperfect. The gas giant planets, particularly Jupiter, are our planetary deflector for errant comets that might collide with our planet. The magnetic field generated by Earth’s molten core deflects deadly particle storms caused by mass ejections from the Sun. The Earth’s ozone layer and our atmosphere minimize the harsh ultraviolet radiation that would, unimpeded, damage living things. So, our de facto planetary defense system is a constellation of fortunate coincidences that favor the development and evolution of life.
To me, the conclusion that these conditions arise from coincidences follows from the fact that they are so uncommon that we find ourselves relatively alone out here in space. Homeostasis, at planetary scale, seems hard to come by – reason enough to celebrate Earth Day, don’t you think?