Principios de Taxonomia

158j 6 Biological Species as a Gene-Flow Community
specimens. Thus, it cannot be ruled out that, in the case of several so-called species,
the trait differences found between those few specimens are only differences in the
frequency distribution of specific alleles, which are the same in supposedly different
species but differ only in their relative quantities. Thus, in some cases, geographically
distant groups that are diagnosed by different traits might not be species; they could
be only local populations or races, such as is the case with different human
populations that are categorized by different allelic frequency distributions in their
blood groups. Alternatively, they could be morphs, for example in the case of varying
phenotypes of the Lepidoptera Papilio dardanus or Zygaena ephialtes (Color Plate 4)
(Chapter 5). Delimitations with respect to gene flow barriers have not been investigated
between most beetle species. Thus, it cannot be ruled out that the current
number of 400 000 beetle species is a wrong number.
In retrospect, it is difficult to understand why sympatric speciation is a relatively
recent discovery and was not recognized several decades ago. The biological
processes that make sympatric speciation possible were sufficiently known in the
former century. Sexual selection of partners (female choice) and monophagy, the
specialization of the organisms of a species to eat a single food plant, have been
known for more than a hundred years, and from these two processes, sympatric
speciation can almost inevitably be postulated. Both phenomena make it easily to
imagine that a slight alteration of traits within a population could lead to the
segregation of a new population and, through this process, to speciation. A high
percentage of insect species is monophagous. In tropical beetles and butterflies, the
estimations come to 20–50% of the species (Schilthuizen, 2001). In temperate zones,
many beetles (particularly weevils Curculionidae) are monophagous (Dres and Mallet,
2002).
Ernst Mayr did not give this concept any special importance because he was not an
entomologist; he was an ornithologist. Because Ernst Mayr dominated the scientific
position on this question for decades in the second half of the twentieth century, the
difference between sympatric and allopatric speciation was given only a very
subordinate importance (Mayr, 2000). Mayr defended the view that allopatric
speciation would be almost the only process of speciation. He insisted in this belief
because he was convinced that the species is a community of organisms that all are
able to reproduce with each other, and that the species, therefore, is a homogeneously
connected gene pool. This scenario meant that only very strong forces would
be able to tear apart a gene pool. From this concept, the allopatric paradigm of
speciation resulted.
The uncompromising dogma of allopatric speciation denotes a Dark Age of
speciation research. It is based on few facts and mainly on authorities who dominated
the field (Tautz, 2009). Modern evolutionary biology, however, demands quantifiable,
testable models, in which the parameters, such as mutation rates, selection coefficients
and migration rates, are measurable. The modern view has given priority to
sympatric speciation because of empirical data. In doing so, modern evolutionary
research approaches Darwin s idea again, after an age of apostasy. Speciation is no
longer first and foremost seen as drift, meaning coincidence without positive
selection, but instead is seen as an intended process of evolution.