[Taxacom] almost unbelievable (advisory)

[John Grehan]

Dear colleagues,

Please do not read any further if biogeographic differences of perspective
or critiques are uncomfortable for you.

As has been documented in the literature, the assumption of chance
dispersal for the origin of allopatry periodically generates 'miracles' and
'mysteries' in the very words of the various authors. Despite this leaning
towards mysticism, faith in chance dispersal continues to be well
entrenched, and in recent decades bolstered by the charade of fossil
calibrated divergence estimates. An addition to this mysticism comes from
Carlquist (1966) in his exposition on long-distance dispersal (Q Rev. Biol.
41) where he declares “A clear understanding of long-distance dispersal is
essential to an understanding of evolutionary trends on oceanic islands,
because immigrant patterns are different from relict patterns.” All very
well, until he runs into the land snail genera Tornatellides, Elasmias, and
Partula. He describes these as having “almost unbelievable distributions”.
Almost, but not quite it would seem. He recognizes that these distributions
would suggest “a kind of relictism” but he ignores this because “islands
they occupy are doubtless relatively recent in geological terms”.

What Carlquist shows here is an inability to rethink his assumptions, even
when the distribution involved is “almost unbelievable”. The distribution
is unbelievable because it does not fit with the theory, and rather than
throw the theory out the data is just ignored. No matter how unbelievable,
the distributions still arose by long-distance chance, even though “further
observational and, if possible, experimental evidence is needed to
demonstrate the nature and causes of 'incompetent' in insular species.” As
with the medical sciences that use pejorative terms such as 'incompetent'
to describe medical defects (all to often in reference to female anatomy),
so to in biogeography are some taxa downgraded to incompetent. This is the
world of 'truth' (as determined by authority) over 'fact'. And of course it
is not as if Carlquist was without alternative possibilities as had already
been made abundantly clear by Croizat and confirmed in great detail in
recent literature. Chance dispersal becomes an excuse for anything and
everything according to whim rather than evidence, and therefore easily
slides into a world of 'science' where miracles, mysteries, and the
unbelievable are quite believable indeed. And this is supposed to be modern
science?

John Grehan