Wednesday, May 04, 2005

Language for Talking, and Thinking, About Evolution

A lot of people recognise that the language we use to talk about evolution is, if taken literally, quite inaccurate. The following are some musings, hastily written up, on how to more accurately describe what is going on. I haven't thought these things through much, and I haven't really looked at whether the suggested alternatives would be suitable for practical situations (like considering whether they are too unweildly or not).

Use 'Situation' instead of 'Environment'

We talk of the creature's environment setting up the selection pressures. Properly understood, there's nothing wrong with this. At the same time, I think the conception of 'environment' most people have can mislead them when thinking about this. The term 'environment' can conjure up the environment of the landscape around the creature, the other plant and animal species. That it can tend to obscure is that the other members of the same species are part of the environment, and that the results of the creatures own behavior is also part of its environment. I think it can also obscure the fact that the environment is not just the physical place, but the unfolding and changing environment over time (over time the selection pressures will change). For these reasons, I think the reality is better captured by the term 'situation'. The creature's situation sets up the selection pressures.

Use 'Optimize' rather than 'Increase'

We tend to say that evolution works to increase a entity's fitness. I think there are two reasons why this can be misleading. It implies that there is some one dimensional value that is being increased... which is okay if you understand that value as an "abstract" fitness. It's just that it doesn't capture well the multidimensionality of the factors that actually make the difference to survival and propagation. "Increase" also suggests a ladder and some path of progress... but this is a bit misleading. For fitness is always relative to the current environment, and what is fit will change as the environment changes. It is not so much that we have steadily increasing fitness, but that the system's fitness "tracks" the changes in the environment. (this is not to say that because 'localized changes' don't always lead to greater general sophistication the biosphere will not end up creating greater complexity over time). For this reason, I think that it is better to talk of creatures fitness being continually optimized rather than continually increasing.

Talk of Natural Selection and Evolution as Products Not Forces, and of optimization potentials instead of implicit goals

When we talk of evolution at work, we tend to say things like "evolution created eyes so animals could hunt their prey". This language is inaccurate because it implies there's an active force pushing, or trying to push, the evolution in a particular direction. But natural selection and evolution is not so much a force that does things, but the product of certain types of situations.

It's the product of situations containing the three factors of variation, heridiblity of that variation, and, basically, competition for survival. When these three factors are present, natural selection and the evolution of forms are the consequences. That is, the natural selection process and the evolution of forms are emergent phenomena.

I started reading Stuart Kauffman's At Home in the Universe last night, and I think there is some of this confusion about evolution in his consideration of how self-organising systems relate to evolutionary processes, though I don't have time to go into the details here (so you can ignore this statement if you want :-)).

We talk of creatures, or evolution itself, evolving some feature for some purpose. This is really just a way of talking and is quite inaccurate. Creatures can't direct their evolution like this, and neither can evolution itself. Evolution does not have goals, and even if it did, it doesn't have any foresight that it could use to reach them. (thinking about evolution as if it did have goals and/or foresight seem to be very common problems). We can much more easily see this when we understand that natural selection is an emergent phenomenom, and I think part of the reason this problem occurs is because of seeing it as some sort of force at work.

It seems difficult to talk of evolution without talking about goals. We talk of evolution as coming up with solutions to problems (it's goals are to solve those problems). What's really going on, however, is that a particular situation provides certain opportunities for creatures to evolve in certain ways. That is, in any given situation, there might be various ways that a creature could potentially evolve that would improve its fitness. If the appropriate mutations happen to occur, the species will move in one or more of those directions. So it's not so much that there is a problem to solve -- a goal to be attained by solving it -- but that the environment possesses opportunities that creatures can happen to evolve towards. I would describe these opportunities as optimization potentials (and remember of course that any change in the environment, including the evolution of a particular species, may change the optimization potentials for it). So natural selection may end up meeting optimization potentials. So perhaps you can say something like "the unfolding situation made use of an optimization potential to evolve feature Y in Xs".

So we can say stuff like "The situation selected for Y", "Optimization emerges from a situation", "Xs evolved feature Y by natural selection's optimization".... but as I said at the start I haven't really thought about using this language in a practical context... and I don't have time for this right now.

1 comment:

  1. Some interesting thoughts here James, I've got some of my own opinions :-).

    In the first section (situation instead of environment) I would more carefully consider who is using the term environment when analysing the correctness of its usage. I certainly consider environment to be more than the physical landscape. My housemate for example is doing her PhD in ecological modeling. She (and people in similar fields) do use the term environment correctly. Factors such as biodiversity, population distribution and the presence of predators / prey are all important consideration for them when talking about environment. You are certainly not going to convince them to change their correct use of environment to situation because a portion of population use the term incorrectly. Isn't it a matter of educating / correcting people on the proper meaning the of term rather than consider it tainted and ditch it for a new one?

    Regarding the use of increase and optimise - note the s not the z you seppo :-). I agree that changes due to natural selection is better expressed using "optimise" rather than increase. There are however cases where an organisms fitness does increase due to natural selection. If a change in the organism results in that organism being far more successful in its environment does this note denote a increase in the fitness with respect to that environment? Success can be measured in a number of ways of course: population density, height in the food chain, susceptibility to harsh environmental changes, etc. Take the example of a carnivore diversifying its diet to become an omnivore. This will likely come about due to changes in its environment, e.g. lack of prey. If by widening its diet it really begins to flourish could this not be called an increase in the fitness with respect to its environment?

    There is some really good reading about this: Carl Sagan's book Cosmos (first 50 pages for so I think) has a very good argument for natural selection and explanation of how it happens. Jared Diamond's books 'The Rise And Fall Of The Third Chimpanzee' and 'Guns, Germs And Steel : A Short History Of Everybody For The Last 13,000 Years'. For something easier and more entertaining I've got the David Attenborough's 'Life of Mammals' DVDs. They've got some interesting explanations about the evolution of mammals.

    Good luck with the PhD...