Skip this thread if Biogeography bores you - especially those recurrent discussions about Croizat

[P.Hovenkamp]

Hi all those not deterred by mentioning the name of Croizat,

Readers without access to the writings of Croizat may from the following
easily gain the impression that Croizat was seeing things (even if not
writing) clearly and was recognizing the importance of  hybridization:

>  More
>>importantly, it is becoming increasingly obvious that reticulate evolution
>>is important in many, if not most, sexual groups.
>
>Actually I would suggest that it has been as 'obvious' all along - just not
>popular with
>traditional evolutionary models (I would call them 'Darwinian' models -
>pejorative or
>not). Croizat referred to reticulate evolution as character recombination.
>
>John Grehan

But this last statement is not exactly true. At least, if Croizat referred
to reticulate evolution as character recombination, he did not do so in
writing. I checked the quite extensive index on "Things and concepts" in
Croizat's "Space, time form" (1964) - unfortunately, his later works are
not so fully indexed.
There are c. 27 entries on character recombination, and c. 20 on
hybridization and interbreeding (as placeholder for reticulation, which is
not a word Croizat indexed on). Only on 2 pages the two concepts are
treated together, and looking up those pages it seems clear that the two
are seen as completely different processes:
p. 273, footnote: "Adding to this the effect of (...some processes...)
hybridizations and recombinations (...more distinct processes...) form
making may reach in time a hardly credible density"
p. 520: "(...) hybridization took place here and there during spells of
mobilism followed in immobilism (C.means during subsequent spells of
immobilism, note PH) by re-combination of characters of permanent nature,
whatever the technical process in detail."
To me, it is clear that hybridization and character recombination are to
Croizat two completely different processes, which need not coincide in time.

This is of course rather surprising, as hybridization offers such a good
expanation of observed character recombination. Yet Croizat seems not to
have thought of that. But then, what he called character recombination is
not what we casually call character recombination.

His concept of character recombination refers to parallel evolution of
similar combinations of character states. To Croizat, organisms were a bit
like banks of dip-switches. Ancestral forms had all the switches in the
same position, and in descendant forms different combinations of switches
would be "up" or "down". Recombination of characters refers to the
possibility that the same combination of "up" and "down" could occur in
"unrelated" forms. Throughout evolution, new "banks" of switches could not
be added: "in evolution old characters are being combined and recombined
without cease rather than new characters constantly called into being" (p.
309). Thus, it is not necessary to invoke hybridization or reticulation -
it was enough to recognize that "form making" could simply flip any number
of switches at any time.

I will not go into John Grehans first statement - that "traditional
evolutionary models" have neglected reticulate evolution. It just shows
that he's not a botanist.

Peter Hovenkamp

P. Hovenkamp
Nationaal Herbarium Nederland - Leiden
PO Box 9514
2300 RA  Leiden
The Netherlands
hovenkamp at nhn.leidenuniv.nl
http://nhncml.leidenuniv.nl/rhb