Posted by: maroonmaurader | November 29, 2009

Pop Evolution

The naive argument in favor of group selection runs: Suppose we had two groups, and in only one of those groups was an altruistic trait was present at high frequency. Then one presumes this altruistic trait, while detrimental to the carrier, would nevertheless help the carriers’ group succeed, and the rising tide would float all boats in that group.

The counter to the naive argument runs: Suppose that within that altruistic group, by random mutation there came to be some individuals who lacked the altruistic trait. Then they would be more successful than other members of their group, so over time the altruistic group would evolve into a non-altruistic group

In The Selfish Gene, Dawkins does a fairly good job of staking out the scarecrow and pulling it apart, then goes on to talk about some limited circumstances in which what *looks* like group selection can be seen arising from individual selection and selection for genes (kinship selection, paired traits, etc. etc.).

The interesting part follows – what is known as the Haystack Model for altruism (or so I gather) runs as follows: suppose we have a situation in which groups are fairly isolated for a number of generations, then all intermingled and new groups are formed (as if, I gather the analogy goes, you had separate haystacks piling up more hay for several years, then tossed them all together and pulled out new haystacks from the main pile). In these limited circumstances, a haystack which has a high frequency of the altruistic gene would tend to grow more than a haystack without the altruistic gene, and thus despite the fact that the frequency of the altruistic gene will decrease in every individual haystack over the intervening time the overall frequency of the altruistic gene can increase; on remixing some haystacks will end up with a higher-than average proportion of the altruistic gene and these haystacks will be the primary genetic contributors to the next round of mixing, etc. etc.

This model does require some fairly restrictive circumstances (although they do occur in nature for some unusual species). The authors of the seminal paper discussing this model, published in 1964, noted the unlikely nature of this system, and thus accepted that it would likely be merely a sideshow to other causes of altruism. So it isn’t the be-all, end-all explanation for altruism, but I thought it interesting enough to note for two reasons.

1. It’s a fairly cool system which leads to what is indisputably group selection, without the need for kinship ties or anything like that.

2. Dawkins completely skips over this method in The Selfish Gene. He published that in 1976, 12 years after the paper clearly and specifically outlining this system was published in Nature. Either his research and scholarship was extremely half-assed when writing TSG (unlikely), or he deliberately decided not to discuss it in his book. If he decided not to discuss it in his book, the generous interpretation would be to say that he simply felt it was not a significant source of altruistic traits and thus not worth discussing; on the other hand he certainly did discuss several other systems for altruism which were as or more unlikely to be found in nature (or Nature, for that matter). So perhaps it’s merely a cynical nature, but I have to lean towards the less-generous interpretation: he didn’t like the fact that there was an absolutely crystal-clear mathematically sound group-selection altruism model out there so he decided to ignore it.


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