Archive for April 2011
Phil Regal kindly drew my attention to a post by Nicholas Wade and hence to Wade’s subject, a recent article by Quentin Atkinson in Science, “Phonemic diversity supports a serial founder effect model of language expansion from Africa” which is a real blockbuster.
Most historical linguists have long argued that historical relatedness among languages beyond families and a few super-families cannot be demonstrated with the kinds of linguistic evidence they prefer, and hence among other things they have been sceptical of the monogenesis theories and evidence of Merritt Ruhlen, Joseph Greenberg, Bernard Bichakjian and others. Atkinson has now exploded the former argument at least with a novel kind of linguistic evidence.
It has long been known that genetic and phenotypic diversity tends to be greatest in the homeland of a species and to decline towards its outermost ranges (e.g. in humans among Africans as opposed to elsewhere). That is because of serial founder effects. Increasingly distant local populations are founded by small, non-random samples of migrants from the less distant. Atkinson has now shown that the same thing obtains for phonemes of languages (the basic set of sounds including vowels, consonants and tones). In 504 languages around the world, Atkinson shows that a language has fewer phonemes the further one travels from Africa (actually specifically from central and southern Africa). Of course this effect of linguistic drift like that of genetic drift on diversity would decline if and when the more distant populations become large as well so Atkinson includes speaker population size in his models but the shadow of history remains impressively robust nevertheless.
The very first post I made to this blog in March of last year supported a common origin of human languages based not on linguistic, but on genetic evidence. I reasoned that if Homo sapiens sapiens share a single or perhaps two common historical origins in Africa 50,000 or so years ago as is currently thought (and nobody thinks language emerged later than that and many think much earlier), then the existence of a one or at most two “mother tongues” seems almost inescapable unless one wished to argue that one or more groups stopped talking for some generations and then began anew again which seems most unlikely. Atkinson does not argue specifically for a monogenesis theory of language. “This region (central and southern Africa) could represent either a single origin for modern languages or the main origin under a polygenesis scenario.” Nevertheless, his research provides strong evidence for the world-wide cultural transmission and evolution of human languages from Africa.
To evolutionists, his evidence is very powerful and the care with which the research was conducted is impressive including controls that biologists like to see such as those for the possibility of non-independence within language families. The quotes that Wade has obtained from traditional historical linguists on the article suggest that this may be the turning point for them to become more open on the subject. I will indulge in one minor complaint about how the ubiquitous developmental rather than an evolutionary analogy holds sway in the title of his comment - “Languages Grew From a Seed in Africa, Study Says”. NO NO NO! Languages (plural) did not “grow from a seed”, they evolved from an ancestor!
Anatol Rapoport, the game theorist of “tit-for-tat” fame among evolutionists, co-authored an article in the first issue of Behavioral Science in 1956 arguing for a detailed analogy between biological and cultural evolution, specifically with respect to language. Many years later he was on my Ph.D. thesis committee comparing theories of change in biology, psychology and the social sciences. The last time I saw him before he died was at a social gathering; he was quite deaf by then and the background noise was considerable. He took a firm hold of my arm and was very intense in telling me that he wanted me to know that phonemes are the (Mendelian) genes of languages. I know he would have loved Atkinson’s article.
The primary structure of a protein molecule is the sequence of amino acids in its chain and its secondary structure is the three-dimensional structure into which the former subsequently folds. On March 10, Nature (here) published a news feature titled “Breaking the protein rules” about the fact that many proteins, in part or in whole, do not assume a unique and fixed three-dimensional secondary structure. The terminology which seems to be emerging among physical chemists/structural biologists to describe the various phenomena involved include “intrinsically disordered”, “flexibility”, “multi-structural states” and “dynamic equilibrium”. Evolutionists too should be very much interested in these phenomena but would likely use different terms – e.g. roughly (secondary) phenotypic plasticity, adaptive plasticity, condition-dependent adaptive plasticity and development respectively.
That single protein molecules can possess such physiological/developmental/behavioural plastic properties (whatever one prefers to call them) normally associated with organisms is nothing less than astonishing. It has implications among other things it seems to me for understanding the origin and early evolution of life. In particular (leaving aside the question of membranes), it makes a protein-first rather than an RNA-first origin of life much more likely.
Early evolution by natural selection could have been based on something in between the very simple morphological (viability selection based on different static structures) and the very complex replicative (which includes heredity and an increase in numbers). In between is a simpler form of ‘repetition’ which could be called “competitive development” (see “The evolution of replication” here gated). The minimal conditions for such a type of evolution is a population of varying individuals, created by the direct action of the physio-chemical environment, in which two complementary alternative states each constructs the conditions that induce and favour the other. For example, polymers which were induced to grow when monomers were plentiful and to assume a more stable configuration when they were scarce would be favoured by selection over those which only grew, only maintained, or attempted to do both but under the reverse conditions because they would repeat their life cycle. Many other possibilities exist beyond growth versus maintenance e.g. growth versus motility with growth at one end and loss at the other resulting in the “tread-milling” form of motility utilized today by cytoskeltal elements for example.
Such a form of evolution could even result in increases in complexity because as many new “births” and deaths took place through time, the range of variation would increase. In any event, the increasing evidence for many “intrinsically disordered” i.e. plastic proteins deserve attention from evolutionists, including those interested in the origin and early evolution of life.