Tangled Bank Theory

Theory that offspring are more likely to survive if they are different than their parents. The assumption propping up this theory is that the local habitat a child is born into is often already saturated with genetically similar relatives and it therefore pays to be genetically different.
This theory has been charged with suffering from the ‘fallacy of affirming the consequent’. The counterargument here is that just because children happen to be more diverse does not mean that diversity occurred simply for the sake of setting children apart from their relatives. Diversity for the sake of genetic distinction is not aligned with how life typically behaves: life prefers to mutate as infrequently as possible. Mutation, and evolution, only when obstacles to life’s continuation arise. Indeed, the mathematical odds of a mutation proving beneficial in the offspring of two parents who have survived until that point within their local environment are outweighed by the odds of a mutation proving harmful. It would therefore be impractical for offspring to trend towards diversity merely to distinguish themselves from their parents; the risk far exceeds the reward.
Articulation of Theory
“As [Michael Ghiselin] put it, ‘In a saturated economy, it pays to diversify.’ Ghiselin suggested that most creatures compete with their brothers and sisters, so if everybody is a little different from their brothers and sisters, then more can survive. The fact that your parents thrived doing one thing means that it will probably pay to do something else because the local habitat might well be full already with your parents’ friends or relatives doing their things.’
     Graham Bell has called this the ‘tangled bank’ theory, after the famous last paragraph of Charles Darwin Origin of Species: ‘It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other and dependent upon each other in so complex a manner, have all been produced by laws acting around us.” (60, The Red Queen)
Fallacy of Affirming the Consequent Counterargument
“The trouble is, all these results are also predicted by rival theories just as plausibly. Williams wrote: ‘Fortune will be benevolent indeed if the inference from one theory contradicts that of another. This an especially acute problem in the debate. One scientist gives the analogy of somebody trying to decide what makes his driveway wet: rain, lawn sprinklers, or flooding from the local river. It is no good turning on the sprinkler and observing that it wets the drive or watching rain fall and seeing that it wets the drive. To conclude anything from such observations would be to fall into the trap that philosopher call ‘the fallacy of affirming the consequent.’ Because sprinklers can wet the drive does not prove that they did wet the drive. Because the tangled bank is consistent with the facts, does not prove it is the cause of the fact.” (61, The Red Queen)
The Lack of Drift Counterargument
“The tangled bank also conflicted with evidence from fossils. In the 1970s evolutionary biologists realized that species do not change much. They stay exactly the same for thousands of generations, to be suddenly replaced by other forms of life. The tangled bank is a gradualist idea. If the tangled banks were true, then species would gradually drift through the adaptive landscape, changing a little in every generation, instead of remaining true to type for millions of generations. A gradual drifting away of a species from its previous form happens on small islands or in tiny populations precisely because of effects somewhat analogous to Muller’s ratchet: the chance of extinction of some forms and the chance prosperity of other, mutated forms. In larger populations the process that hinders this is sex itself, for an innovations is donated to the rest of the species and quickly lost in the crowd. In island populations sex cannot do this precisely because the population is so inbred.” (62, The Red Queen)
Platonic Bias Counterargument
“It was Williams who first pointed out that a huge false assumption lay, and indeed still lies, at the core of most popular treatments of evolution. The old concept of the ladders of progress still lingers on in the form of teleology: Evolution is good for species, and so they strive to make it go faster. Yet is stasis, not change, that is the hallmark of evolution. Sex and gene repair and the sophisticated screening mechanisms of higher animals to ensure that only defect-free eggs and sperm contribute to the next generation – all these are ways of preventing change. The coelacanth, not the human, is the triumph of genetic systems because it has remained faithfully true to type for millions of generations despite endless assaults on the chemical that carry its heredity. The old ‘Vicar of Bray’ model of sex, in which sex is an aid to faster evolution,  implies that organisms would prefer to keep their mutation rate fairly high — since mutation is the source of all variety — and then do a good job of sieving out the bad ones. But, as Williams put it, there is no evidence yet found that any creature ever does anything other than try to keep its mutation rate a low as possible. It strives for a mutation rate of zero. Evolution depends on the fact that it fails.
     Tangled banks work mathematically only if there is a sufficient advantage to being odd. The gamble is that what paid off in one generation will not pay off in the next and that the longer the generation, the more this is so — which implies that conditions keep changing.” (63, The Red Queen)
The Red Queen by Matt Ridley

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