I thought the case had been laid to rest weeks ago when somebody brought up
Drosophila. Intensive selection hass been carried out for over 60 years at
25 generations per year times hundreds of cultures per lab times dozens of
labs (probably hundreds) worldwide. When the flies escape they waste no
time in reverting to wild type. But in no case has a "new species" been
produced, say nothing of an improved variety. If change were not limited, we
would certainly see some evidence for it here. In Hawaii, over 600 species
of Drosophila are accounted by various authorities. All Drosophila,
probably derived from a single progenitor that arrive in the Islands early
in their history. They are not becoming other things, they are not
postulated to have been derived from other things. Thats evidence for the
limits of variability if there ever was any. The plants of the Hawaiian
Islands in the composite family, bresumably derived from a single original
colonizing member, probably of the tarweed alliance, from California.
Members of the group in Hawaii include the famous silverswords of Maui, with
a growth habit much like yuccas, the greenswords of Kauai, also yucca-like,
and Dubautia latifolia which looks like a trailing vine. While the
morphologies vary considerably, nobody would have the least difficulty
classifying them as sunflowers. They are interfertile with the California
tarweed, incidentally. Then we come to bacteria. E. coli has been
intensively selected for a few quadrillion generations in the laboratory.
While a few enzymes can be found to change, and they do shift in population
characteristics so that new strains occur even in the lab when you don't
want that to happen, they are all easily recognized by any beginning student
of microbiology as E. coli. There are as many additional examples as there
are studied species.
Art