Archive for September 2018
Tangled Trees?
David Quammen book, The Tangled Tree: A Radical New History of Life was reviewed in Nature Aug. 2 by John Archibald (not incidentally the author of a book on symbiosis). It was also reviewed in the New York Times Book Review on Aug 14 by Erika Check Hayden under the title of “Uprooted”. On Aug 19, Quammen himself published an article in the New York Times Magazine titled “The Scientist Who Scrambled Darwin’s Tree of Life”.
Quammen’s book is largely about Carl Woese, the great pioneer of molecular phylogenetics, who in 1977 with coauthor Fox, made clear from their study of a component of ribosomes (protein factories in cells) that there are three not two domains of life – the Archaea in addition to Bacteria and organisms with nucleated cells like plants, animals, fungi and some unicellular organisms (Eukarya). Woese was apparently not a fan of Darwin – he commented to a prospective co-author of a book to be titled Beyond God and Darwin, “Jan, you accord Darwin so much more substance than the bastard deserves”.
Anyway, the theme of the reviews and article (and I assume of the book which I have not, or at least not yet read), is that life is better described as a “network”, a “tangled web”, or a “topiary” rather than Darwin’s tree because of the existence of horizontal i.e. lateral gene transfer (LGT ). LGT can take place by transformation (taking up DNA from the environment), transduction (a piece of host DNA carried to another organism by a virus), and conjugation (bacterial “sex” which is unidirectional). Unfortunately Hayden casually equates LGT with “swapping genes” which is exactly what it is not i.e. bidirectional rather than unidirectional. Not does its existence invalidate Darwin’s tree metaphor for evolution as these authors generally seem to think. Quammen’s article is illustrated with outrageous illustrations of what looks like an early hominid with a chicken’s head, one with a fish’s head, a human with what looks like a frog’s body between head and shoulders on top and lower legs and feet on the bottom. Perhaps we should not blame Quammen for these illustrations but the point is that because laterally transferred DNA is normally just a tiny part of the genomes of eukaryotes, the best metaphor I have seen is “trees with some cobwebs”. (In 2005 Liza Gross in PloS attributes this metaphor to Fan Ge and coauthors.)
Yet, once anisogamy (micro and macro gametes) have evolved, then sex again becomes unidirectional, i.e. from males or male functions to females or female functions. But that is unidirectional within a species – indeed the ability to interbreed after Mayr is what is most commonly said to define species boundaries. Of course Woese was right that we know very little of what went on in the early history of life. However, only if hybridization (sex between members of different species) were rampant in the Eukarya could Darwin’s trees truly be said to be entangled and despite the occasional case there is no evidence of that.
Autistics, Saints & Sinners: Ecological and Social Evolution
It is common in evolutionary theory to distinguish between ecological and social evolution – evolution in interaction with the physical environment and other species versus that in interaction with other members of the same population or species. Of course in ecological evolution individuals compete with respect to some ecological phenomenon, but the difference is that it is a ‘scramble’ i.e. contact and interaction are not involved as they are in social evolution which includes phenomena such as kin selection, reciprocal altruism, various kinds of ‘contests’ involving contact and aggression, sexual selection etc.
A case might be made that there is actually something else and not just an absence of autistic characteristics at the other end of the autism spectrum. Most fundamentally, autism may reflect an excessive preoccupation with, and behaviour oriented towards the physical and ecological environments, “things” (which may include animals), at the cost of neglect of the social. V. K. Jaswal and N. Akhtar in an article on autism in Behavioral and Brain Sciences in June (see also their article in the New York Times, July 13) describe motor stereotypes but not other restricted and repetitive interests and activities. After all, it is no secret that Silicon valley is populated by austicish individuals preoccupied with their computers, programmes and gadgets. At the other end of the spectrum “saints” (Williams syndrome?) but also “sinners” (psychopaths) reflect an excessive preoccupation with, and behaviour oriented towards the social environment at the cost of neglect of the physical and ecological. The distinction between saints and sinners simply reflects whether the prevailing social orientation at that end of the hypothesized spectrum tends towards cooperative (altruistic – + or mutualistic + + interactions) versus conflict (selfish + – or spiteful – – ones). Individuals with Williams syndrome are exuberantly social including linguistically but in addition to lacking many ecologically-oriented cognitive skills such as spatial ones, lack social caution or fear. Of course, few individuals are at either of these social extremes, just as few are at the ecological or social extremes, most being somewhere closer to the middle.
Unfortunately, because the same ecological versus social distinction could be drawn about any selection process, none of this speaks to which one or ones of several possible selection processes – biological evolution, development, individual learning or sociocultural evolution is responsible for giving rise to autistics versus saints and/or sinners. Jaswal and Akhtar argue that autistics do not lack social motivation or interest. Instead, there may be a lack of ability or even adaptive or cultural reasons to avoid engaging in various forms of social interaction towards that end of the spectrum. It seems likely that genetics and/or development is involved but Jaswal and Akhtar make a good case that individual learning (“adaptation”) and/or cultural transmission are also part of the story.
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