Evolution of the concept of species
The farmers probably had not formalized a concept since the very origin of the livestock. Plato speculate that because we see horses and cows, but never a hybrid of both, it must exist somewhere in an ideal form that forcing an animal to be one or the other. Aristotle prefer to avoid its share these speculations and simply list them in the Organon what he observes. Albertus Magnus them try to turn later.
Empirical concept, the concept of species has evolved with time and history has been marked by the thought of great naturalists like Linnaeus, Buffon and Darwin. In the eighteenth century, species were considered as the result of the creation of God and, as such, were regarded as objective and immutable realities. Since the advent of evolutionary theory, the concept of biological species has changed significantly, but no consensus has been reached on its definition.
- Initially, we considered the species as fixed entities defined by morphological criteria. This typological design has found its apogee in the work of Linnaeus and the establishment of collections of individuals "typical" case.
- According to Cuvier, a case can be defined as the collection of all organized bodies born from each other or from common parents and those who resemble them as they resemble each other.
- This concept has evolved into a species 'taxonomy' for which the mathematical analysis of a large number of criteria is sufficient to establish a threshold from which one could say that two individuals belong to different species. The case would then be a useful concept that real biological entity.
- The shortcomings of this method led to another approach is the concept of biological species based primarily on criteria interfécondité and isolation (Ernst Mayr, 1942), again with some difficulty to differentiate such species that are naturally not in contact, etc..
- This has led to amend the definition of species including an environmental component. Beginning in 1963, Ernst Mayr defines species as a reproductive community of populations, reproductively isolated from other communities and which occupies a niche in the special nature. This operational definition of the species is not without problems (eg, recognition of niches).
- Much of these problems can be avoided if one considers the history of living beings. Evolution is a historical process and species are the result of the collapse of species that preceded them (speciation). All the above criteria need to be correlated with genealogical relationships.
A species is a single lineage that has its own evolutionary tendencies and its own historical destiny (according to Delforge P Guide Orchids of Europe ... and Delachaux Niestle 1994). The concept of "fate" has no scientific basis "its own history" corresponds better to what is seen as the subject of ongoing research. The concept of "single lineage" must also be qualified because, as noted, some community is possible between some closely related species: it may result in fertile offspring characteristics most suited to their environment, which form perhaps time a separate species.