Computer Simulation of Multilevel Selection and Evolution

The topic of "Multilevel Selection" has been going around lately, in the context of how biology and the genetic selection that Darwin described, meshes with culture and religion and other "meme" selection that has been advocated by Richard Dawkins and his advocates. A similar concept has been put forward by E. O. Wilson, who calls it "sociogenetic" selection, to indicate that the culture as a whole works together with the genetic material to produce some sort of emergent collective organism (Wilson looked at ants which would have to be the most startling example of a highly organized social structure operating almost like a single entity, see also "Sociobiology").

Well, there has been some disagreement between Dawkins and Wilson over the operational details of this mechanism, and on top of that, David Sloan Wilson is also buying into the discussion and he often calls it "group selection", but as far as I can tell, David Sloan Wilson uses "multilevel selection" and "group selection" quite synonymously. Here is a recent video on this topic:

EIGHT CRITICISMS NOT TO MAKE ABOUT GROUP SELECTION

Major topics in science typically include a zone of consensus among the experts, based on past progress, and a zone of current controversy still being thrashed out. The topic of group selection is unusual in the degree of ignorance among professional evolutionists who are experts on other topics, but whose ideas about group selection remain sadly out of date. Their ignorance interferes with the peer review process when they are called upon to review articles on their area of expertise that are written from a multilevel perspective. David Sloan Wilson and Omar Eldakar review eight criticisms that no one should be making about group selection, based on a commentary published in the academic journal Evolution in 2011.

My Take on the Selection Theory

I've come to the conclusion that evolution must happen on every level simultaneously because there is no way to justify a privileged position for any particular evolutionary unit. Of course, in some cases, picking a particular unit of reproduction to base your theory on can be an excellent simplification, and every theory requires suitable choice of simplification, but just remember that it is nothing more than a convenience.

I'm certainly not a biological specialist, so I dislike bilologists using words like "altruism" and "group selection" to mean something special to biologists, but just about every non-biologist would take them as meaning something else. The constant confusion between concepts such as "altruism", and "reciprocal altruism" (which should more correctly simply be known as "trade") tends to spring from people getting anchored into a particular way of looking at things. That is to say, they focus entirely on the individual and completely ignore group effects, or focus entirely on the group and ignore the individuals.

In particular, "group selection" is a terrible term to use and should be completely avoided. I'm sure David Sloan Wilson understands what he means by it, but the impression any normal person would get is that somehow selection amongst individuals is no longer happening, but of course selection is always happening at both levels -- amongst the individuals, and also at the group level as well. The term "multilevel selection" conveys this concept clearly, making it the preferable term.

Computer Simulation of Biological Problems

Many practitioners of the physical sciences have an uneasy relationship with computer simulation -- and rightly it should be uneasy. Simulation should be treated with suspicion because essentially a computer can be programmed to do anything you like, doesn't mean it every happens out there in the real world. Thus, often the results of a simulation do nothing more than demonstrate the predjudice of whoever designed and programmed that software.

The thing about evolutionary biology is nearly all of it is observation, and drawing conclusions based on extrapolating the observed case. Here is the answer, I'll make up a question that seems to lead toward that answer. The evolutionary biologists are a bit weak when it comes to experimentation and predicting the results of their experiments. Laymen think that studying evolution ends up nothing more than a collection of "just so stories"; great as a comforting explanation for what you already know, but useless for producing genuine new discoveries that you didn't already know. Once again, the "just so story" method of retrospective explanation often tends to reveal more about the predjudice of the person explaining, than it does about the system itself.

Computer simulation provides some sort of workable and safe option for putting evolutionary theories to the test. Like all tools it must be used appropriately. Let's suppose you want to simulate a real physical system, like you want to discover exactly what the average global temperature of the Earth will be in 100 years as a result of additional CO2. Those sort of simulations require incredible attention to detail, and careful callibration, especially if you regard the difference between 1 degree warming and 2 degrees to be highly significant. The simulation presented here is not even an attempt to model any physical system, it is only a demonstration that the basic mechanism being discussed can work. There has been no attempt to callibrate this or to model any particular cultural or religious difference here. It is a very simple and generic model, designed to be a minimalist starting point to encourage experimentation.

Some of the arguments levelled against the "multilevel selection" theory are along the lines of, "It is illogical, and it simply cannot work at all."

Hopefully, this simulation does at least prove, yes the mechanism can work, there is no particular mathematical rule that prevents it, because it has been demonstrated. That does not prove that exactly this mechanism is at work in any real life scenario that you care to name; however since the result comes out as an emergent property of a very simple model, and since all of the assumptions that go into it are quite reasonable and plausible, we might expect to find some similar mechanism at work in the real world.

Fundamental Components and Assumptions of the Simulation

Program Code Download

A more detailed code walkthrough and documentation is available, to touch on the technical details of the implementation (also for people who wish to make their own modifications and run their own experiments, which is encouraged). The doxygen-generated documentation is also here.

If you want to make your own movie, the three steps involved are driven by the scripts above, and you will need to install "gimp" and "theora_encode" which are commonly available on most linux distributions. TODO: the GIMP Animation Package (GAP) might be able to output to ogg/theora and do this in one single step, or I should write a program that can do it in one step.

Results and Movies

NOTE: Microsoft users probably want to download VLC Media Player to be able to watch movies in OGG format.


Final frame output (mobility limited to 0.1).
DOWNLOAD MOVIE: HIRES (24M) or LORES (2M)


Final frame output (mobility limited to 0.2).
DOWNLOAD MOVIE: HIRES (24M) or LORES (2M)


Final frame output (mobility limited to 0.3).
DOWNLOAD MOVIE: HIRES (24M) or LORES (2M)


Final frame output (mobility limited to 1.0: maximum mobility).
DOWNLOAD MOVIE: LORES (2M)

Conclusions

From both the frame images and the movies, we see the unmistakable formation of stable groups, and survival competition between groups (some grow, others are extinguished). Increased opportunity for mobility causes larger final groups and more consistent elimination of smaller groups (note that in no case are individuals forced to be mobile, because mobility itself is an evolvable characteristic).

The groups must represent an emergent feature that can compete via the aggregrate effect of large numbers of individual interactions. Multilevel selection has been demonstrated to be viable.

Comments

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