Conclusion




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Conclusion

In summary, my claims are:

  1. The "replicator" terminology, as promulgated by Dawkins and Hull, suffers from significant, and confusing, internal contradictions. It would be best abandoned.

  2. The units of selection in Darwinian evolution are lineages rather than actors.

  3. More precisely, the units of selection are S-lineages. Unfortunately, these are somewhat complex and even nebulous entities. In particular, they are not simply groups of actors which share some overt, inherited, "trait" ; nor are they simply "species" in any conventional biological sense. I suspect that S-lineages can only usefully be identified in a relational sense, in the context of a particular episode of Darwinian selection. That is, we identify an S-lineage not so much by any similarity among its members, as by the competively significant difference between two (or more) S-lineages.

  4. Actors may have a von Neumann-like genetic architecture. This is generally the case for contemporary terrestrial organisms. In this (special) case, an S-lineage can typically be identified or marked by a particular segment of the genetic description, shared by all members of the S-lineage. This makes it tempting to regard this genetic "tag" (or "gene" ) as being the S-lineage, or to regard this genetic level of description as uniquely preferable for describing Darwinian selection dynamics ( "genic selectionism" ). This temptation should be resisted. A particular genetic tag can only identify a selectively important "trait" in the context of the actors which express or translate it; to put it another way, the "meaning" or "decoding" of a particular tag can vary (in principle by an arbitrary amount) from one actor to another, even in the "same" lineage; furthermore, in principle, the same "trait" can be correlated, independently, with multiple distinct genetic "tags" .

  5. The logic of Darwinian evolution requires replication with some kind of "heritability" so that coherent S-lineages can form and compete. However, it does not require any particular kind of hereditary mechanism, and, in particular, does not require that the component actors have a well-formed von Neumann style genetic architecture.

One reader of an earlier draft of this paper wondered what (if any) pragmatic implications it had for actually designing artificial evolutionary systems. I can only answer for myself of course. The most important implication for me is that, once the mystique of "genic" selectionism is dispelled, we can usefully ask how it is that von-Neumann style genetic organisation can spontaneously come into existence at all. As long as "replicators" (in Dawkins' narrow sense of fragments of genetic material - or even lineages thereof) are considered as necessary pre-requisites for Darwinian evolution, we can hardly even formulate this question, never mind answer it. But once we separate the notion of genetic organisation from the notion of the units-of-selection, we can envisage a form of ALife investigation in which we do not already "wire in" a genetic architecture, but ask how it could arise and be refined - by a process of Darwinian (but not yet "genetic" !) evolution. This is, of course, a fundamentally different direction from "conventional" GA or evolutionary strategy investigations. I suggest that it is a worthwhile alternative to pursue.




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gif So: Does it or Doesn't it?



McMullin@eeng.dcu.ie
Mon Mar 4 14:08:30 GMT 1996