From time to time I think about a passage in a book I read several years ago, Power, Sex, Suicide: Mitochondria and the Meaning of Life by Nick Lane. He’s setting up the context to talk about the purpose of different organelles and chemical processes in cells, and he takes a moment to acknowledge the fact that using the word “purpose” in this context is a little problematic.

I don’t remember his exact words, but the gist of it was this. If you aren’t interested in turning to supernaturalistic explanation (e.g. “God created certain chemical processes with the intent that they play a certain role or achieve a certain goal”) then what exactly do we mean when we say that a physical process or thing has a purpose?

We use the word “purpose” all the time in this context, and its meaning is transparent and immediate: the purpose of the heart is to transport oxygenated blood through the body; the purpose of the liver is to remove toxins from the blood. But what do those phrases really mean? If you don’t believe in a “creator” who made these things with conscious intent, and you don’t believe that hearts and livers themselves are cognitively complex enough to have their own mental states and awareness, and you understand that we use the word in a way that implies that even if no human being on the planet had any knowledge of what hearts do or that they even exist that would not change the truth-value of the statement “the purpose of the heart is to transport blood through the body… then whose purpose are we talking about?

Lane calls it a difficult problem and side-steps it in his book, which was very wise and completely appropriate. The book had other things to address, and a good author knows when not to get side-lined into deeply complicated tangential topics. So… good on him.

But I’ve thought about that question a lot over the years.

This issue has been talked about for a very long time. It’s Aristotle’s “final cause”, which he thought of as critical to understanding physics in a way that seems ridiculous today. It’s one thing to say “the reason the seed exists is to make a tree”, but in 2020 C.E. in Western Culture it feels much weirder to say “the reason the rock falls is because its goal is to reach the center of the earth.”

The weird tension between non-supernaturalistic explanation in science, on the one hand, and the strong intuitive link we have between purpose and consciousness, on the other hand, has lead to a lot of bad assumptions and bad thinking over the years as well. The late 1800’s and early 1900’s had a lot of people thinking of evolution in terms of “purpose” and Aristotle’s “final cause”, which lead people to think of evolution as directing species toward some “higher” form, which in turn lead to all kinds of crap about evaluating who was “more evolved” than whom.

A contributing factor in all of this is that reflex tendency people have to think of the operation of biological systems in terms of purpose.

The early part of the 20th century saw the development of a lot of sophisticated thinking about control systems: feedback loops, self-correcting organizations, homeostasis, and so on. Gregory Bateson proposed that a self-correcting feedback loop is both necessary and sufficient requirement for a system to act with a purpose (or to phrase it a different way: to have goals or intentions).

I don’t remember the exact wording, but I remember that he uses the example of a room being controlled by a thermostat. There is a regulatory feedback loop: if the temperature is below the set-point, it causes the heater to activate and the temperature to rise; if the temperature is above the set-point, it causes the heater to turn off and the room can cool. This constitutes the minimal system, Bateson argues, where we can intuitively and sensibly use words related to intentionality. The structure and organization of the mechanics of the room-thermostat-heater system are in equilibrium when the room is at a particular temperature. When the room is not at that temperature, the system will act to change it. Just based on observing its behavior, we can say the system wants the room to be a particular temperature.

It strikes me (as it strikes many people) to be a bit oversimplified, but it’s interesting for the direction of this line of thinking. If we don’t want to invoke supernatural consciousness, but we do want to acknowledge that it is meaningful to say things like “the purpose of the heart is to pump blood”, then we need to build up a theory of purpose that that is rooted in the physical structure and behavior of things. What is it about the physical organization of items in the material world that makes us intuit that hearts and livers and mitochondria all have a purpose independent of whether or not any human being is contemplating them… but rocks do not?

It’s an amazing question, and I feel like we (human beings in general) could learn a lot about the nature of consciousness and reality by developing a really solid theory of what “purpose” actually is. It’s a necessary step in furthering our understanding of subjectivity and consciousness.