The hierarchy of life

The theory

In my last post, I broke my own rule of trying not to mention in a post a technical term that I haven't explained in previous posts. OK, I had excellent reasons to break the rules, but still, I'd like to compensate for it by explaining immediately afterwards.

The term I used was the hierarchy of life. This is a very useful concept when you are trying to understand how living systems operate at different scales. Small living systems organize into bigger living systems, all the way up to the whole Earth (to use the technical word, the whole biosphere). To make it easier to understand, I'll use human beings as an example, and I'll skip some of the levels that are less interesting.

• Cells: At the lowest level, or bodies are made up of cells. (Well, this isn't really the lowest level, but the things that happen at a smaller scale than this aren't fascinating unless you like peering into electron microscopes). Cells are nothing but tiny living things, that live their little independent lives, and can happily survive on their own if the conditions around them match exactly what they find inside our bodies. Cells are constantly dying and renewing inside our bodies. Most of the cells that make up your body now didn't exist seven years ago.
• Organs: Cells make up all your organs: the heart, the brain, the stomach, etc. Each organ is a relatively independent system: if you hurt badly your leg, your heart will continue beating without any trouble.
• Human bodies: Your body is made up of all your organs working together in a beautifully orchestrated system. Human beings are quite independent of each other and can survive on their own for long periods, but without each other's help their physical and mental wellbeing is in danger.
• Villages, towns and cities and their bioregions: People live together in populations of different sizes. Some living creatures create their own ecosystems around them, and humans are particularly impressive in that respect. They bring all sorts of materials from long distances to build their refuges, and they eliminate most other living creatures except a few that they like (grass, park trees and pigeons) and a few that have become extremely good at adapting to the conditions they create (cockroaches and rats). Cities need agricultural land around them to support them, and together they can be called a bioregion, that can exist relatively independent of the surrounding land.
• The Earth: There is a rather fancy, long and complicated word to describe all the bits of the Earth that have been touched by human presence: the anthroposphere. By now, this is pretty much the whole Earth, so we'd better call a spade a spade. Life on Earth depends on the Sun to continue existing, but apart from that, it exists quite independently. James Lovelock is famous for his theory that the whole Earth is a self-controlling system, though some people have their doubts, and they ask: and how did it become self-controlling? I'm agnostic on the question of whether the Earth has been a self-controlling system for millions of years (though the evidence is compelling). But I'm pretty certain that by now, when humans are controlling just about all the ecosystems, the Earth is definitely self-controlling. Whether the Earth is currently doing a great job of controlling itself is a matter of debate, the latest news on climate change suggest it's doing quite poorly.

This is a useful overview of all the scales in the bigger picture, and I won't repeat this again. From now on, most of the posts are going to focus on scales somewhere in between individuals and cities, with the occasional jump to the whole Earth.

The practice

Experiment 1

Watch Powers of Ten. Just watch it. It should be required at schools. I never figured out how anybody is supposed to understand their place in the Universe without this.

Experiment 2

The hierarchy of life, as I described it, is done in a few big jumps. There are actually a lot of smaller intermediate levels. Try to think all the intermediate levels between an individual and a whole city.

There isn't a single correct answer to this one. Try to discover several possible ladders. How much influence do you have at each of those levels? Which ladder makes you look more important? Does any ladder make you think you need to learn more about something?