Willmann 2003
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Willmann 2003

DisciplinaPrincípios de Sistemática2 materiais48 seguidores
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From Haeckel to Hennig: the early development of phylogenetics
in German-speaking Europe
Rainer Willmann
Institut f\u20acuur Zoologie und Anthropologie, Berliner Str. 28, D-37073, G\u20acoottingen, Germany
Accepted 10 September 2003
An outline of the development of phylogenetic thinking and methodology in German literature published between 1862 and 1942
is presented. Central European biologists and palaeontologists of the first post-Darwinian generation of biologists holding evolu-
tionary views were directly stimulated by Darwin. Members of the second generation, mostly born after 1850, were largely influ-
enced also by colleagues of the first post-Darwinian generation, mainly by Haeckel. Among them were O. Abel, V. Franz, R.
Hertwig, A. Naef, L. Plate, and R. v. Wettstein. Opinions on the relationship between systematics and phylogeny differed con-
siderably. Many authors admitted that phylogeny must be mirrored in systematics but at the same time shared Haeckel!s views on
classification, which permitted paraphyletic groupings. Particularly Abel and Naef took systematics several steps further, and many
important elements of phylogenetic systematics were developed several decades before Hennig. Naef presented a definition of a
phylogenetic group that exactly matches Hennig!s definition of monophyly. He also formulated a species concept that was implicitly
based on reproductive isolation. This was an important presupposition for viewing speciation as the splitting of a stem species into
daughter species. However, many authors of the first half of the 20th century repeated old, but established views on phylogenetics,
while others overlooked or misunderstood earlier progressive views thus causing slow development of phylogenetic systematics in
Central Europe. Its development almost stopped between 1925 and 1950, because of a widespread shift towards typology and
extreme idealistic morphology. During that time very few persons such as W. Zimmermann and W. Hennig assembled elements of
phylogenetic systematics and combined them with their own thoughts to create a sound theory and methodology.
! 2003 The Willi Hennig Society. Published by Elsevier Inc. All rights reserved.
In \u2018\u2018The Origin of Species,\u2019\u2019 Darwin (1859) outlined
his view of the structure of the natural system. \u2018\u2018The
natural system is founded on descent with modifica-
tion,\u2019\u2019 he wrote, and \u2018\u2018From the first dawn of life, all
organic beings are found to resemble each other in
descending degrees, so that they can be classed in
groups under groups\u2019\u2019 (1859, p. 411). A genus consists
of several species, \u2018\u2018and the genera are included in, or
subordinate to, sub-families, families, and orders, all
united into one class\u2019\u2019 (1859, p. 413). Thus a main
principle of biological classification based on the idea
of evolution is the subordination of group under
group. \u2018\u2018The characters which naturalists consider as
showing true affinity between any two or more species,
are those which have been inherited from a common
parent, and in so far, all true classification is genea-
logical\u2019\u2019 (1859, p. 420). Darwin added that genera with
a remote ancestor have less in common than genera
descending from a more recent ancestor but in 1859 he
did not delve deeper into the matter.
Although evolution was discussed long before \u2018\u2018The
Origin,\u2019\u2019 it was only through Darwin!s work that the
theory of descent led to discussions about phylogenetic
relationships and phylogenetic methods. However, the
content of Darwin!s brief outline of the principles of
classification from 1859 differed considerably from what
Hennig attempted. Darwin (1859, p. 420) believed \u2018\u2018that
the arrangement of the groups within each class, in due
subordination and relation to the other groups, must be
strictly genealogical in order to be natural; but that the
amount of difference in the several branches or groups
[. . .] may differ greatly [. . .]; and this is expressed by the
forms being ranked under different genera, families,
sections, or orders.\u2019\u2019 Referring to the only illustration in
his book he added (1859, p. 422) that \u2018\u2018[i]f a branching
diagram had not been used, and only the names of the
0748-3007/$ - see front matter ! 2003 The Willi Hennig Society. Published by Elsevier Inc. All rights reserved.
Cladistics 19 (2003) 449\u2013479
groups had been written in a linear series, it would have
been still less possible to have given a natural arrange-
ment; and it is notoriously not possible to represent in a
series, on a flat surface, the affinities which we discover
in nature amongst the beings of the same group. Thus,
on the view which I hold, the natural system is genea-
logical in its arrangement; but the degree of modification
which the different groups have undergone, have to be
expressed by ranking them under different so-called
genera, sub-families, families, sections, orders, and
classes\u2019\u2019 (see also Darwin, 1859, p. 456). It should be
stressed that these phrases are all that was read of
Darwin by German, Austrian, and Swiss authors inter-
ested in classification, while in other writings Darwin
expressed more differentiated views on the topic (Pa-
dian, 1999). Though Haeckel did not discuss Darwin!s
writings in detail, his classifications appear to have been
congruent with what Darwin had proposed in 1859.
Although Padian (1999, p. 363) is certainly correct in
saying that it is not historically faithful to graft the
taxonomic philosophies of the modern synthesis or
those of phylogenetic systematics onto Darwin!s ideas
and practices, a comparison of these with Haeckel!s
thoughts is possible, as Haeckel stimulated phylogenet-
ics (his term!) more than any other biologist of his time.
Haeckel!s view was largely what over a century later
would be called \u2018\u2018evolutionary classification.\u2019\u2019 However,
the presuppositions of Darwinian and evolutionary
classifications respectively were entirely different as
Darwin (1859) was not explicit on (and possibly not
aware of) the nature of a taxon as a product of phylo-
genesis, i.e., that it consists of a stem species and all its
descendants. In contrast to classifications sensu Darwin
and Dohrn, 1867, Hennig laid the fundamentals for
phylogenetic systematization.
In other works Darwin described the structure of the
\u2018\u2018natural system\u2019\u2019 in slightly different words: \u2018\u2018[. . .] the
co-descendants of the same form must be kept together
in one group, apart from the co-descendants of any
other form; but if the parent forms are related, so will
their descendants, and the two groups together will form
a larger group\u2019\u2019 (Darwin, 1871, p. 181). \u2018\u2018The co-de-
scendants of the same form\u2019\u2019 are key words. Darwin
obviously meant that groups should contain forms such
that they correspond to the monophyletic groups of
Hennig (Nelson, 1974, p. 457). However, phrases such
as these had no influence on early post-Darwinian sy-
stematists and they remained almost unnoticed by
phylogeneticists until Darwin!s view on taxa was ana-
lyzed during the cladistic systematization vs. evolution-
ary classification debate. And nowhere did Darwin
really tackle the difficulties that may be met in the at-
tempt to transform a family tree into a classification
(Crowson, 1959, p. 109). It appears to be revealing that
there is almost no mention of phylogenetics in Kohn!s
1138 pages collection of essays on Darwin and the
Darwinian heritage. Historians of biology may simply
have overlooked systematics because of their concen-
tration on evolutionary mechanisms (Bowler, 1996).
The frame and indeed the main source of Hennig!s
thoughts on systematics were views on phylogenetics as
developed in Central Europe. As Craw (1992, p. 68) put
it, \u2018\u2018Darwinism found more supporters among biologists
and the general intellectual audience in Germany than in
any other country.\u2019\u2019 As early as 1864,