Geography Reference
In-Depth Information
Ameghino claimed that South American mammals predated and were an-
cestral to all others in the world. Many paleontologists engaged a debate
with Ameghino, but finally the study of fossil invertebrates by Ortmann
showed that Ameghino's correlations, based only on mammals, were wrong
(Bowler 1996).
Daniele Rosa (1857-1944), an Italian lumbricologist (a specialist in
earthworms), was an evolutionary biologist. In 1918 he published Ologen-
esi, where he developed a theory that emphasized evolution due to internal
causes. Rosa's fundamental statements were the following: Evolution de-
pends not only on external but also on internal factors to such an extent that
it continues even in a uniform environment; the direction in which internally
driven evolution acts is independent of the variation of external factors; and
even so, evolution is not indefinitely linear; on the contrary, it is dichotom-
ously ramified (Baroni-Urbani 1977). The theory of hologenesis assumes
that cladogenesis proceeds dichotomously (Luzzatto et al. 2000). In biogeo-
graphy, Rosa (1918) postulated cosmopolitan distribution of primitive spe-
cies. This is relevant because instead of a “vacuum” theory, in which areas
are devoid of taxa, this provides the possibility of a “primitive cosmopolit-
anism,” a prerequisite for vicariance. Rosa's (1918) arguments against dis-
persal are similar to those of panbiogeographers and cladistic biogeograph-
ers in more recent times (Luzzatto et al. 2000).
In 1922 English botanist John Christopher Willis (1868-1958) published
Age and Area . In this topic, he postulated that age as an explanation of dis-
tribution was simpler than natural selection. This hypothesis was born when
the author had the opportunity to study the flora of Ceylon (now Sri Lanka)
(Willis 1915) and neighboring countries and observed that many endemic
species were confined to small areas of the island, other species also dis-
tributed in India had larger areas, and those ranging beyond the peninsula
had the largest areas. When defining very rare, rare, and rather rare species
( fig. 3.1 ), Willis observed that very rare species occurred in one place only,
rare species in areas about 10-30 miles across, and rather rare species
in areas 30-60 miles across. He found that the idea that endemic species
were local adaptations could not explain the observed facts. Some mechan-
ical explanations were necessary, and Willis thought it was the age of the
species. His hypothesis was formulated as follows:
The area occupied at any given time, in any given country, by any
group of allied species at least ten in number, depends chiefly, so
long as conditions remain reasonably constant, upon the ages of the
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