[Taxacom] almost unbelievable (advisory)

[John Grehan]

It was the distribution pattern he found unbelievable, not the question of
chance dispersal which he already accepted. No one has yet demonstrated
that ingestion and survival in bird guts has anything to do with the origin
of the Tornatellides distribution.

On Tue, May 19, 2020 at 8:42 PM Kenneth Kinman via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> Hi All,
>        Long distance dispersal of snails such as Tornatellides can occur
> when migrant birds ingest the snails and they can pass relatively unharmed
> through the digestive tract.   Carlquist presumably wouldn't have known
> this.  If he had known this, he wouldn't have found it so unbelievable.
>                                 ------------------Ken Kinman
>
> https://www.discovermagazine.com/planet-earth/snails-cross-continents-by-flying-inside-birds
>
>
> https://blogs.scientificamerican.com/guest-blog/bird-guts-not-muddy-feet-may-help-snails-migrate-overseas/
>
>
> ________________________________
> From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of John
> Grehan via Taxacom <taxacom at mailman.nhm.ku.edu>
> Sent: Tuesday, May 19, 2020 7:03 PM
> To: taxacom <taxacom at mailman.nhm.ku.edu>
> Subject: [Taxacom] almost unbelievable (advisory)
>
> 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
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