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Levels of Natural Selection January 21, 2009

Posted by tcb1370 in Philosophy of biology.
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There are many theories about the question of “At What Level Does Natural Selection Operate”, but I’ve chosen to focus on just three mainstream theories.

Group Level

Group selection is commonly referred to as “Multi-Level Selection Theory“.

D.S. Wilson defines group selection in this way:

Group selection promotes fitness of groups, relative to other groups in the global population. The levels of selection are not always in conflict.

It’s easy to fall into thinking about individual selection, when one is trying to imagine group selection taking place, but these following examples are sometimes used to differentiate between group selection, and the levels below it:

  • Molecular reactions initially “competed” against each other, but eventually became cooperative and formed into simple cells.
  • Simple cells once competed against each other for resources and eventually became complex cells working together.
  • Multi-cellular organisms arose from groups of complex cells.  We consider a multi-cellular organism to be one organism now, but it may have evolved as such because of the benefits to replication that groups of cells received when cooperating.
  • Eusocial insects like bees, wasps and ants are groups that act as a single organism in some ways, and compete against other like groups.  Note: This type of colony has actually evolved 11 different times independently.  I find that to be very interesting.

Group selectionists also seem to use the idea of Koinophilia as evidence of their theory.  Basically, by only choosing mates that have the most average characteristics of their population, a group can fend off selfish individuals from taking advantage of the group’s cooperation.

For more information on group selection, I would suggest this paper by D.S. Wilson and Elliott Sober: Re-introducing Group Selection to the Human Behavioral Sciences.  Their main point is stated here in the abstract:

We show that the rejection of group selection was based on a misplaced emphasis on genes as “replicators” which is in fact irrelevant to the question of whether groups can be like individuals in their functional organization. The fundamental question is whether social groups and other higher-level entities can be “vehicles” of selection.

Gene Level

Gene level selection, also known as “Selfish Gene Theory” really seems to have been made most popular by Richard Dawkins, in his book “The Selfish Gene”.  In this book, Dawkins explains the idea of replicators as the underlying cause of all evolution and describes the organism as a machine that perpetuates its replicators (in this case, genes).

He uses Evolutionarily Stable Strategies to show that most of the behaviors we see today in organisms can be explained by the way that replicators fall into certain patterns that do not allow other organisms to take advantage of them.  These strategies may not be the most optimal in terms of overall benfit to the organism – for example, a strategy where an organism never fights another organism would be beneficial to everyone in the population – but they prevent a mutant aggressive organism from being born that would invade and inevitably spread through the population.

I found his paper Burying the Vehicle, to be very interesting because it refuted many of Wilson and Sober’s claims about ‘vehicles’ of selection.   I think it can be summed up pretty well here:

Natural selection chooses replicators for their ability to survive in an environment that includes other replicators and their products. Sometimes cooperation among replicators is so strongly favoured that units coherent enough to be called vehicles emerge. But just because a vehicle may emerge at a given level, we have no right to assume that it will and I believe the evidence will show that at most levels it usually doesn’t. The question, “What is the vehicle in this situation?” may be no more justified than “What is the purpose of Mount Everest?” Ask rather “Is there a vehicle in this situation and, if so, why?”

Individual Level

Individual selection seems to be the most commonly accepted view of natural selection.  Selfish Gene Theorists agree, in that since it is only through an individual that a gene may express its characteristic, the individual may rightly be thought of as the unit of selection.

For more information on the various levels of Natural Selection, I would take a look at the Wikipedia page Unit of Selection as a starting point.

Some authors and books I would suggest would be:

  1. Dawkins’ The Selfish Gene
  2. Frans de Waal – a primatologist who writes a lot about the origins of altruism
  3. Elliott Sober – a philosopher of science, who has an interest in biology
  4. PZ Myers – I can’t help myself. PZ is my favorite science blogger, so I have to include him.  He’s done a few controversial things in the past to make his points, but he really knows biology.  He is my daily source for information about evolutionary theory, so I would highly recommend him.