Monday, 25 February 2013

Replicators revisited

While I've long argued against using the "replicator" terminology, Eörs Szathmáry, has stuck with it - in the following papers:

  • Szathmáry, Eörs (1999) Chemes, Genes, Memes: A revised classification of replicators. Lectures on Mathematics in the Life Sciences. 26, 1-10.
  • Szathmáry, Eörs (2000) The evolution of replicators. Phil. Trans. R. Soc. Lond. B 29 November 2000 vol. 355 no. 1403 1669-1676.
  • Szathmáry, Eörs (2006) Cultural Processes: The Latest Major Transition in Evolution.
  • Fernando, Chrisantha, Karishma, K.K. and Szathmáry, Eörs (2008) Copying and Evolution of Neuronal Topology.
  • Fernando, Chrisantha and Szathmáry, Eörs (2009) Chemical, Neuronal, and Linguistic Replicators.
  • Fernando, Chrisantha, Goldstein, R. and Szathmáry, Eörs (2010) The Neuronal Replicator Hypothesis. Neural Computation 22 (11): 2809–2857.
In 2011, one of his students, István Zachar published their Ph.D. thesis on the topic:

Replicator Formalism - A general account of replication The document lists five general, "intuitive" requirements for replicators:

  1. Autocatalysis: potentially autocatalytic mode of generation.
  2. Similarity: potentially above-chance similarity between parent and offspring.
  3. Informational: ability to pass on information to offspring. This is a requirement for informational replicators.
  4. Inclusivity: The widest definition has to include genes, memes, and possibly other entities as well.
  5. Specificity: The definition must be able to distinguish between various multiplying entities: genes, memes, simple chemical cycle intermediates, lipid vesicles, kinetic multipliers, organisms, and higher-level entities in a clear and exact way.
The document asks:
  1. What is the qualitative and quantitative difference between genes, organisms, general autocatalytic intermediates and other multiplying entities?
  2. What are the basic concepts behind the Mullerian criteria multiplication, heredity, and variability, and what part do they play in replication?
  3. What is replicator identity and similarity? When do we say that two replicators are identical?
  4. What is common and distinctive of genes and memes? What is the definition that puts memes and genes into the same box but not organisms?
On reflection, I don't think Universal Darwinism really needs this concept. It can do very well using the concepts of heredity, copying and reproduction. Distinguishing between the reproduction of organisms and the reproduction of DNA molecules just isn't a particularly urgent or important task. This is a good thing - since there's no hard line to be drawn between them.

Attempts to distinguish replicators from organisms seem to have mostly led to anti-group-selection rhetoric that claims that groups don't replicate - aren't "units of selection" and so can't be the beneficiaries of adaptations. Alas, these arguments aren't worth too much.

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