Ernst Mayr suggested an eminently more sensible definition - macroevolution occurs only at the level of genus or even higher (an idea he may have stolen from yours truly, btw).
That seems somewhat unlikely since, as I pointed out earlier, it's a meaningless definition. Principally for the reason that there's no agreed on definition of 'genus'. How many organisms are included within a genus is a matter of fashion, aesthetics and what seems most convenient for taxonomists. As an example, titi monkeys have been for a long time been classified as one genus,
Callicebus. Recently, though there has been a push by some taxonomists to recognise three genera of titis,
Callicebus,
Cheracebus, and
Plecturocebus. The long discussion of why can be
read here for free if you really want to, but it can be briefly summarised thus: 'There are loads of species of titi monkey, and we can split them into three clear groups on genetic, morphological and ecological grounds. We want these groups to be different genera.'
By your genius-level definition, then, would recognising the common ancestry of titis be macroevolution now? Was it a few years ago, before anyone recognised different genera? What's the point of such a meaningless and arbitrary definition, and how can it help if we're not even in agreement on whether evolution is a thing.
I went and dug out some Mayr to read what he actually said. From his 1942 book,
Systematics And The Origin Of Species:
quote:
Under the term microevolution such evolutionary processes are understood as occur within short spaces of time and in lower systematic categories, in general within the species (hence also, intraspecific evolution). By the term macroevlution we understand the development of major evolutionary trends, the origin of higher categories, the development of new organic systems - in short, evolutionary processes that require long periods of time and concern the higher systematic categories (supra-specific evolution). There is only a difference of degree, not one of kind, between the two classes of phenomena. They gradually merge into each other and it is only for practical reasons that they are kept separate.
Seems to me that he saw the term, much like genus, as having an imprecise definition that varies according to convenience.
™ Version 4.2
