BIOLOGICAL SPECIES: CONCEPT, CHARACTERISTICS AND EXAMPLES - BIOLOGY - 2024

A biological species is a population of animal individuals that can reproduce with each other and give rise to fertile offspring. However, they cannot reproduce with members of populations of a different species. This concept was initially proposed by Ernst Mayr and Theodosius Dobzhansky in 1940.

The first criterion to distinguish a species is that the animal population has a common ancestry. This implies that members of a species must be able to trace their ancestry back to a “common ancestral population”.

The panda bear is an example of a biological species

Next is the criterion that a species should be the smallest group that can be distinguished between organisms that share patterns of ancestry and descent.

Finally, the last fundamental criterion is that of the existence of a reproductive community. In this way, members of the same species should form a "community" from which other species are excluded due to reproductive isolation, a criterion of significant importance for the conception of biological species.

Species concepts

A photograph of Ernst Mayr, who formulated the biological species concept (Source: Evolutionforever, derivative work Lämpel via Wikimedia Commons)

There are different concepts of species. None of them is the “definitive” concept and neither is completely true for all living organisms, so the definition of a species is still a matter of discussion today.

- Typological concept

Carlos Linneo. Source: Alexander Roslin

Carlos Linnaeus and many other naturalists up to Darwin used a species concept that still has a certain validity today: the typological concept. In the era that preceded Darwin, a species was considered an immutable entity (that did not change in time) and independent.

Each species was distinguishable by defined and fundamental characteristics, that is, a species was treated as a group of organisms that shared the same essential characteristics, mainly morphological.

The species were also defined based on a “type specimen”, which was deposited in a museum for the consultation of those who wanted to determine if a similar organism belonged to the same species.

- Evolutionary concept

With the advent of Darwinian and neo-Darwinian theories about evolution, the typological concept of species fell into disuse.Many researchers began to consider that species were historical entities, whose unique features and properties were subject to variations and modifications over time (dynamic and not static).

The exact definition of this concept proposes that a species is a lineage of "ancestor-descendant" populations that maintains its identity with respect to different lineages and that, in addition, has its own evolutionary tendencies and its own historical "destiny".

- Phylogenetic concept

According to this concept, a species is a basal group of organisms, distinguishable from other similar ones, within which a pattern of descent and descent can be seen.

- Biological concept

In 1940, the neo-Darwinists T. Dobzhansky and E. Mayr proposed the biological concept of species inspired by Darwin's theories. The concept, worked on and improved by Mayr, was defined more or less like this:

"A species is a reproductive community of populations, isolated from other species from the reproductive point of view, which occupies a specific niche in nature."

This concept "revolutionized" the way of conceiving species, since it does not take into account any morphological characteristics, but rather the intraspecific reproductive capacity and the occupation of the same ecological niche (for which they share certain ecological characteristics as well).

Disadvantages of this concept

According to the biological concept of species, which is applicable only to sexually reproducing individuals (who can mix to produce fertile offspring), those organisms that only reproduce asexually cannot be grouped into species, which means a problem for This concept.

In addition, this concept also suggests that species are distinguished by the defined niche in which they inhabit, which can generate conflicts if it is thought that a species has spatial and temporal dimensions.

This concept may falter if those species that have truly wide ranges of distribution, whose ecological characteristics can be highly variable, as well as some aspects of their morphology, are taken into account.

Characteristics of a biological species

Whale shark. Source: FGBNMS / Eckert

Biological species, according to this concept, are groups of organisms that live in the same ecological niche (they share the same geographic distribution patterns and some of their most important ecological characteristics) and that can reproduce to produce viable and fertile offspring.

Since members of populations of the same biological species can only reproduce with each other, a biological species has a certain set of varied alleles (“gene pool”) and intraspecific variations exist, but may not be very important.

Despite the fact that the members of the same biological species are distinguished (according to the concept) by their reproductive isolation with respect to other species, the members of the same group or biological species share some morphological attributes among themselves, in addition to multiple genetic attributes.

The reproductive isolation of biological species can occur in different ways. In this sense, pre-zygotic and post-zygotic reproductive isolation mechanisms have been defined.

Pre-zygotic mechanisms refer to those by which the fusion of two gametic cells between different species does not occur, although copulation may occur; whereas postzygotic reproductive isolation causes the generation of unviable or simply infertile offspring.

Examples of species

Donkeys and horses

Photograph of mules (Source: Elgaard via Wikimedia Commons)

The biological species concept can be well exemplified by the case of horses and donkeys. When a mare and a donkey reproduce, the fruit of this union corresponds to a "hybrid" individual known as a mule.

Mules are perfectly healthy organisms, expressing characteristics of the two species from which they originate. However, they are sterile animals, so they cannot reproduce to form a new individual.

Human beings

As long as organisms that reproduce sexually are considered, the examples of biological species are indeed numerous. Humans are a clear example of a biological species, since the first case of a human who has reproduced with some other animal species and has had fertile offspring, or offspring at all, has not been reported.

Dogs

Dogs, a highly relevant domesticated species for man, all belong to the same species, which is why multiple mixtures of different breeds can occur, whose offspring can reproduce and give rise to new perfectly fertile individuals.

Other

Endemic species of Mexico.

Species of Mexico in danger of extinction.

References

1. Brusca, RC, & Brusca, GJ (2003). Invertebrates (No. QL 362. B78 2003). Basingstoke.
2. Gallardo, M., H. (2011). Evolution: The Course of Life (No. 575 G 162).
3. Häuser, CL (1987). The debate about the biological species concept ‐ a review. Journal of Zoological Systematics and Evolutionary Research, 25 (4), 241-257.
4. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). New York: McGraw-Hill.
5. Sokal, RR, & Crovello, TJ (1970). The biological species concept: a critical evaluation. The American Naturalist, 104 (936), 127-153.
6. Solomon, EP, Berg, LR, & Martin, DW (2011). Biology (9th edn). Brooks / Cole, Cengage Learning: USA.