Saturday, 14 March 2015

Parent-offspring asymmetry

In evolutionary processes, sometimes parents and offspring are indistinguishable and other times, they are very different.

Newborn human offspring are very different from their parents. They are much smaller and more helpless. By contrast, bacteria generally reproduce via binary fission - and parent and offspring are identical. DNA molecules produce offspring DNA molecules where it makes no sense to ask which molecule is the parent and which is the offspring.

In cultural evolution we also have a mixture of parent-offspring symmetry and asymmetry. Copies of the GPL are mostly identical and they spread via cloning rather like a virus. By contrast, many complex human memeplexes undergo a developmental process within the human mind. It is usually pretty easy to distinguish between the memes in the teacher and the memes in the student: the student's memes are less mature and well developed.

I think whether that newborn offspring identical to their ancestors (or not) is a reasonable classification criterion for evolutionary entities.

However, there can sometimes be some issues. For example, sometimes what seems to be a newborn which is identical to its parent can - on closer inspection have some systematic differences. FOr example, with DNA strands there is a parent-offspring relationship: the 'parent' strand is used as the template for the formation of the 'offspring' strand. However, this relationship is not obvious unless the copying process itself is witnessed. Once the copy has been made it is hard to distinguish it from the original - unless the copying fidelity involved is poor.

A similarly problematical example from the cultural realm is photocopying. A photocopy might appear to be identical to the original document. However a detailed examination will probably reveal some differences - allowing the original to be distinguished from the copy.

This issue is an imperfection in this classification scheme - but hardly a terminal one. It is useful to distinguish between organisms that develop significantly after birth from those that do not.

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