Wednesday, April 17, 2013

On The Use Of The Word Archaic In Writing About Evolution

In an interesting article on hybridization in human evolution in Earth Pages by Steve Drury I came across the following sentence:

Multi-regional evolution posits archaic populations  originally living in and outside Africa being  gradually assimilated by migration and interbreeding that transferred modern traits everywhere yet retained some regionally distinct features of the archaic groups. The first model clearly has to be modified as evidence accumulates for some degree of hybridisation with archaic groups outside Africa. The second of the two pre-genome ideas seemed to be rendered obsolete by the DNA evidence for significant interbreeding between early immigrants from Africa and Eurasian and Asian populations of earlier archaic migrants – Neanderthals and Denisovans respectively – whereas modern Africans show no sign of recent contact with these archaic groups. However, not all regions of the genome have been examined for signs of more universal hybridisation.

What meaning should one read into the term "archaic". A common misconception is that archaic means "less evolved".  But when migrants from Africa came in contact with Neanderthals or Denisovans or some other unnamed human population, it was a meeting between two human populations who had been evolving for the same amount of time since their divergence from a common ancestor. So there is no sense in saying that one group was less evolved than the other.

So then,  archaic could mean that at the time of contact one population was resident in the area for a long period. They were early migrants into that area, making them an old population. Or, archaic could mean that one population had been isolated from the common gene pool for a longer period of time than the other, meaning, one population branched off much earlier from the ancestral population.  The branching event could have been a migration resulting in genetic isolation. Or, archaic could mean that one population resembled the common ancestor more than the other population i.e. it had retained many ancestral traits and had undergone less morphological changes, while the other population had accumulated more new morphological traits since diverging from an ancestral population. In all the above three, the term archaic could well be used to describe a living population. Lastly,  archaic could be used to describe features that are now extinct.

When "modern" humans migrating from Africa met Neanderthals in Europe, they were not meeting  people who were less evolved , but people who had been evolving along a different trajectory for as long as any other then living branch of humans. We think of the jutting brow ridges and barrel chest of Neanderthals as archaic because that trait is no longer visible or very rare in humans living today. We see it only in fossils. They are features of antiquity.

But at the time "modern humans" met Neanderthals there was no archaic or modern in the sense of less or more evolved. Neanderthals were archaic in the sense that they were the earlier residents of Europe and had been genetically isolated from African populations for a long time. Both populations had some archaic traits in the sense of traits retained from their ancestors. Both also had changed morphologically, having evolved some new traits since their divergence from a common ancestor.  There was no way of knowing then which collection of traits would survive till today to be categorized as modern and which would be consigned to archaic in the sense of being extinct.  At that time they were just two sibling populations with their own unique evolutionary histories.


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