Principios de Taxonomia

64j 3 Is the Biological Species a Class or is it an Individual?
With this presentation, the fundamental difference between the system of chemical
elements and the system of biological organisms becomes apparent. A class of
particular chemical elements in a group on the periodic table are far more than a class
of objects with similar traits. There is a scientific justification for the trait identity that
is based on a consistent natural law. The group of noble gases is not a polythetic class
formation due to the coincidence of several properties, but rather a natural kind due
to a physical law.
In contrast, the system of animals and plants is not based on natural laws that
stringently dictate which selected organisms must be grouped into a natural class.
The grouping of butterflies and moths into the order Lepidoptera due to their scaled
wings and other traits does not include any law contained in the scaled wings and
other traits. Every attempt to group biological organisms into classes has not lead to
natural kinds. The only way to group biological organisms into natural entities is the
combination of the different organisms by their relational cohesion. The natural law
does not come from properties but from relational descent and gene flow cohesion,
and for that reason, butterflies and moths form a natural group.
That the classes of the chemical elements are based on a physical law also follows
from the fact that extraterrestrial planets and solar systems are composed of exactly
the same elements as Earth because the same natural laws apply there. If aliens one
day land on Earth, they will certainly be composed of the same atoms that we are, but
even if their properties were identical to ours, they would never be humans. The only
imaginable possibility for them to be humans would be if they were our relatives, that
is, that they had traveled from Earth to the distant planet or from the distant planet to
Earth some time ago.
3.11
The Relational Properties of the Members of a Species are the Essence of the Species
If biological organisms are grouped into classes according to trait resemblance, then
these classes are not natural. However, because taxonomists apparently have no
problem with assigning individual organisms to species, there is something more
fundamental than trait resemblance that leads to the certainty of the existence of
species (Davies, 2005; Okasha, 2002). Species appear as natural groups, but cohesion
by mutual relational is what makes the groups natural. What is it that makes a Tiger a
Tiger? It is not the striped fur but the connections with its ancestor and with its sexual
partners.
Biologists and philosophers of biology typically regard species essentialism as
incompatible with modern Darwinian theory. Samir Okasha, however, has shown
that the standard antiessentialist considerations only show that species do not have
intrinsic essential traits (Okasha, 2002). However, this does not mean that the
biological species does not have any essential properties; relational properties are
the essence of a species. If an individual Tiger did not share a common ancestor with
all other Tigers, it could not belong to the species Tiger. All of its properties are rather
unimportant; it only must belong to one and the same descent community.