Principios de Taxonomia

50j 3 Is the Biological Species a Class or is it an Individual?
independently from each other but instead by descent. The Darwinian theory of
descent implies that the discovery of a Tiger that shares all of the properties of a
terrestrial Tiger on a distant planet must be interpreted as a migration of the Tiger
from the planet Earth to a distant planet, or in turn from the distant planet to the
Earth. If the Tiger has migrated to the planet from Earth, then it is not independent
from the terrestrial Tiger but part of the group of Tigers.
Therefore, these assumed distant Tigers cannot be independent elements of a class
but rather parts of one single whole. A descent community cannot occur simultaneously
and independently at different locations, so the species as a group of
organisms that are bound to each other cannot be a universal. A descent community
cannot be a class.
If, however, these assumed Tigers on the distant planet are independent occurrences
(i.e., the result of a de novo origin but nevertheless identical to terrestrial Tigers
in all of their traits), then these so-called Tigers would be the result of convergent
evolution. However, under the conditions of parallel evolution these apparent Tigers
on the distant planet would not be considered Tigers.
This fundamental difference between chemical elements and living beings is
based on the fact that chemical elements are not subject to evolution. Elements arise
in the stars; they are not born by parents, and they are not subject to mutation and
selection. Tigers cannot arise by astrophysical processes. Tigers only propagate an
entity that already exists. This realization dates back to Louis Pasteur who stated that
life arises from preexisting life, not from non-living material. This awareness is
summarized in the phrase Omne vivum ex vivo, Latin for all life [is] from life, also
known as the law of biogenesis. As a consequence of the law of biogenesis, living
beings cannot be universals or classes.
The opposite of a universal or class is the individual. The perception that biological
species are individuals has been founded mainly by Michael Ghiselin (Ghiselin, 2002).
Here the term individual is used in the philosophical sense, meaning an entity that
is unique and exists only once in space and time. The concept of an individual should
not be confused with the use of the word individual in everyday life, in which
the term individual refers to a single organism, not to the totality of the group.
An individual can only occur once in the world. In contrast, a class is always a
universal. A class is a set of objects with some coincident traits. A group of objects is
always either a class or an individual; it cannot be both simultaneously, nor can a class
and an individual be mixed. The difference between a set of objects as a class and a set
of objects as an individual is a fundamental one. As an individual, the species Tiger
is perceived in an entirely different way ontologically than it would be perceived as a
class. As an individual, the Tiger s physical properties do not affect why all Tigers
belong to a group. The physical properties cannot define group affiliation of the
members of an individual. A single Tiger only belongs to the individual species
Tiger because it has a relational connection to other organisms, namely, a descent
relation (Chapter 7) or a gene-flow relation (Chapter 6), not because it has particular
properties. Of course, the individual species Tiger has a number of physical
properties, but these do not define why particular organisms belong to the individual
species Tiger nor is the individual species Tiger defined by physical properties.