That a cat and a bird are not organisms of the same species we all know, don't we? However, it is not always so simple to know whether or not an organism is of the same species What other. Appearance, although often helpful, is not a reliable criterion, since there are many organisms of the same species, but with very different characteristics.
Several people have already tried to conceptualize a species, but this conceptualization is not simple and goes through several difficulties. Although there are concepts that are more accepted by specialists, there is still not one that fully explains all the complexity of a species.
→ Biological species concept
The most accepted and most widespread biological species concept is the one proposed by Mayr in 1977. According to this concept:
“Species are groupings of interbreeding natural populations, reproductively isolated from other similar groups"
In a simplified way, we can say that individuals of the same species are those that manage to cross or that have the potential to cross naturally and live in the same population. Note that, in this case, there is no mention of appearance, which, despite being used for identification, is not a decisive criterion in this process.
Mayr's biological concept has flaws concerning reproduction of organisms, for example. When we talk about interbreeding species, we exclude some beings, such as bacteria. In these groups, the reproduction is of the type asexual and therefore there is no crossing. Furthermore, bacteria cannot have the concept of reproductive isolation applied.
There is still another problem: species such as mare and donkey, for example, are able to cross and originate the mule, a hybrid. The emergence of hybrids occurs when individuals of different species interbreed and give rise to a new individual, which is generally not fertile. In this case, it is clear thatalways only individuals of the same species reproduce.
In case of fossils, the situation is even more complicated, since it is impossible to answer exactly about its reproduction. Therefore, the definition of species in Paleontology is analyzed more at the morphological level, since this is the characteristic that can be observed.
→ Other species concepts
There are several species concepts, such as species recognition, phenotypic species concept, and phylogenetic species concept. These concepts seek to complement the biological concept and correct some problems.
According to the cspecies recognition concept, individuals of the same species are able to recognize themselves as potential sexual partners. already the phenotypic concept says that individuals very similar to each other and different from others are of the same species, even if they are prevented from reproducing. already the phylogenetic concept explains that organisms of the same species share a single derived characteristic that is not present in other groups.
It is noteworthy that the concept of species must be chosen by the researcher based on the data available in his research. As said, although appearance is not the best criterion, in the case of fossils, it is sometimes necessary. For the general public, however, the most applied concept is the biological one.
By Ma. Vanessa dos Santos
Source: Brazil School - https://brasilescola.uol.com.br/biologia/conceito-biologico-especie.htm