Science - February 3, 2010

Life is about organization

Gerard Jagers op Akkerhuis has come up with a new theory about what life is. He feels it is not enough to just look at reproduction and metabolism. 'In my opinion you should get just as high a prison sentence for shooting an intelligent robot as for shooting a police officer.'

Gerard Jagers op Akkerhuis
It is possibly the most difficult question we can come up with: what is life? Ecotoxicologist Dr Gerard Jagers op Akkerhuis of Alterra has a simple answer. The definition of life and death follows directly from his Operator Hierarchy, a theory for which he will soon be receiving a PhD from Radboud University Nijmegen. Life is a question of having the right organization.
The theory Gerard Jagers op Akkerhuis has come up with did not just occur to him one afternoon. He has been working on it to a greater or lesser degree for fifteen years. It all began when he was thinking about how toxic substances operate in the environment for his work at that time. 'Toxic substances can have an effect at different levels: the cell, the organism, a population or the entire ecosystem. If you want a clear-cut theory, you first need to introduce a clear-cut order in those levels. Only then will you be able to talk about effects cutting through all those levels.' That quest led to the beginnings of the order that is now termed Operator Hierarchy. 'I was lucky', is how Jagers op Akkerhuis describes his insight. 'If you hit on something like that then it's simply a lucky strike. That's how it felt too: as if this was really something special.'
The Operator Hierarchy places all physical and biological 'components' in a strict, logical and coherent order in a single chart. The word 'component' in inverted commas covers not just fundamental components like atoms and molecules but also organisms such as bacteria, human beings and intelligent, self-aware robots. Jagers op Akkerhuis uses the collective term operator for all these components. Each subsequent step in the chart leads to a more complex component with a higher degree of organization. He has introduced the rather difficult concept of closure to describe such a step up the organization tree (see the box). The result of this ordering is a chart that is highly reminiscent of the Periodic Table of the Elements.

Are you the new Mendeleev?
'I don't know about that. At any rate, I didn't get my inspiration from the Periodic Table. I was restructuring an ecological hierarchy and it was only afterwards that it turned out to look a lot like a kind of periodic table for the complexity of components. I have put physical and biological components in a single chart. I have called these components operators because otherwise biologists will complain that a cow is not a component. That was one of the communication problems when I was developing this theory. I had to find names for new concepts and sets of objects. For example, I call all creatures with a nervous system memons. That is a crucial distinction. This distinction within the multi-cellular eukaryotes is not made in the usual evolutionary trees. Brains are seen as an organ rather than a new level of organization.'
Making a distinction
Jagers op Akkerhuis uses the term closure to refer to an aspect (a mechanism or a structure) that distinguishes operators from each other. Each subsequent operator follows on from the previous operator through the addition of a new closure. Eukaryotes are derived from unicellular organisms by introducing a nucleus. Animals (memons) follow on from multicellular eukaryotes through the addition of a nervous system. The cell nucleus and nervous system are examples of closures.  Another example: 'A bicellular organism is the smallest multicellular unit. The cells are physically attached to each other - that is the structural closure. But they need to be able to communicate with each other so there also needs to be a functional link. The structural closure is a form, the functional closure a process. The component needs to be closed in both form and process.'
The definition of life based on the Operator Hierarchy is almost trivial. Life is all operators from the prokaryote up. So a unicellular organism is alive, as are plants and animals of course. But a self-aware robot is alive too. Thus Jagers op Akkerhuis has reduced the definition of life to the definition of organization. 'Yes, that's right. I have linked the systems-theoretical definition of life to all operators above a certain level. Then death is the loss of the highest organization level, the highest closure, of the component in question. For example, if you are talking about an animal, then the highest closure is the nervous system, the neural network. If an animal loses that, it is no longer an animal but a multicellular organism such as a plant. If a human being's brains no longer work and he can only continue to exist through artificial respiration, then he has become a plant. He is still alive but he is no longer a human being. As a matter of fact, that's how doctors look at it too.'

So life arises, emerges, when you reach a certain basic level of organization?
'Yes, I think purely in terms of organization levels. Defining what life is means drawing a dividing line somewhere in the chart. We do that at the level of bacteria. That could have been anywhere else, only then we would have had a different understanding of what life is. For example, you could draw an upper limit above the cellular memons (humans and most animals) and then call artificial life something different. I don't do that. By the way, there is no such thing as artificial life. If the structure is right, then it is life. In my opinion you should get just as high a prison sentence for shooting an intelligent robot as for shooting a police officer.'

So you are severing the link between life and concepts like reproduction and metabolism?
'Try freezing a bacterium until there is no longer any metabolism or reproduction. My definition says there is still life because the structure is intact and fits the chart criteria, even if the organism has been 'turned off'. Biologists often say evolution means life and life means evolution. But neither is true. Not all life can reproduce and thus evolve - take the mule. And not everything that reproduces and evolves is life - take prions and viruses.'
Jagers op Akkerhuis is not the first to attempt a definition of life. Overviews have been compiled with more than a hundred definitions. But in his opinion such definitions usually get it wrong because they focus on the processes of living things. 'They try to define life by taking combinations of facultative characteristics such as metabolism and reproduction. But whatever combination you choose, there's always some organism that doesn't meet the criteria. That is why I took the fundamental step of looking at obligatory characteristics: what is the minimum requirement to have life at a particular level? In other words, what characteristic should a component have as a minimum at a particular level in order to have life at that level? It is not primarily about the processes. The structure is more important for a classification than the process that causes it.'

What does the scientific world think of your work?
'They are uneasy with it. A lot of people see the definition of life as a very theoretical subject.  They have no idea how they should judge the Operator Hierarchy. I may have thought up something different, but other people need to appreciate the value of it too.'

And now?
'I have not been cited very much yet. My idea is rather fundamental and theoretical and there are not many people working in this area. On the other hand, there is a lot of interest in applications such as the definition of life or the prediction that robots will follow on from humans in evolution. But I hope people will still be citing the Operator Hierarchy in a hundred years' time. That is perfectly possible because the idea is highly fundamental. Or I have made a terrible mistake, in which case it will be shot down because I made a blunder somewhere or because someone else has a much better idea. It is possible -  that's science.'