Phylogeny and ontogeny: what they are and how they differ

Phylogeny and ontogeny are two words that often appear together, which makes, on more than one occasion, one think that they are synonymous. But they are not.

The first describes the evolutionary relationship between the species that populate the earth, while the second is responsible for studying the maturation process of living beings.

However, and despite the fact that they do not mean the same thing, the theory of evolution has not been able to avoid relating them, and with good reason, since, in essence, both describe what the origin is and what types of changes occur in that complex idea that is at lifetime. Let's see it next.

• Related article: "The theory of biological evolution"

Phylogeny and ontogeny: what do they describe in biology?

The words "phylogeny" and "ontogeny" were introduced in 1866 by the German naturalist and philosopher Ernst Haeckel, very inspired by the work of Charles Darwin and who popularized the work of the English naturalist in German lands.

The word phylogeny was used to describe the historical and generic development of a species

, that is, how a species has changed over time and how it can be related to other species within the tree of evolution.

The word ontogeny would describe individual development, that is, the maturation of an organism. Nowadays both terms have more or less the same idea behind, although, and thanks mainly to the advances of the genetics and the development of technology such as X-rays, both biological fields have been increasing their knowledge.

What is phylogeny?

Phylogeny (from Greek "phylon", species, race, and "genesis", origin, generation) is the study within biology that is dedicated to studying the origin and development throughout the evolutionary history of the species that populate the planet, in addition to elaborating genealogies that relate.

The starting point to know the phylogeny of living beings is to establish similarities between different species. This is done by analyzing their DNA, morphology, embryology, similar use of limbs, and other aspects. In the event that in two or more species similarities are found in those aspects mentioned, it can be said that there must be some genetic relationship or evolutionary resemblance.

There are species that may have a very close evolutionary relationship, since it may be the case of that share a common ancestor, that is, a species of which both modern species descend. This is the main question that the phylogenetic study occupies, and it is what allows to elaborate very sophisticated phylogenetic trees.

These trees, which currently choose to be based on studies of genetics, constitute the bases on which phylogenetic knowledge is based. They are scientific classifications that allow you to see how closely different species are related, both modern and past and extinct, and see how these relationships have changed over the course of evolutionary history.

On the other hand, the kinship relationships between species serve to establish classifications of living beings in several hierarchically organized categories. Here you can see an example, with the categories arranged in columns from the most general to the most specific:

It must be said that these phylogenetic trees are not a modern thing. Already in "The Origin of Species" (1859), by Charles Darwin, a tree is drawn in which the English naturalist tries to represent, visually, how different species are related modern.

• You may be interested: "Charles Darwin: biography of this famous English naturalist"

On human phylogeny

The human phylogeny is the study of origin and development throughout evolutionary history, both of the modern human being (Homo sapiens sapiens) and of their hominid predecessor or related species, as would be the case of the Neanderthal.

In the human phylogenetic tree we also find other primates, such as the modern prosimians, the monkeys of the New and Old World, the gibbon, the orangutan, the chimpanzee and the gorillas.

Modern phylogenetics considers that they are part of the human phylogenetic tree, based on the findings found to date, the following species and genera: Pliopithecus, Dryopithecus, Oreopithecus, Ramapitecus, Australopithecus, Paranthropus, Australopithecus advanced, Homo erectus, Homo erectus soloensis, Homo neanderthalensis, Homo rhoesiensis, Y Modern homo sapiens.

What is ontogeny?

Ontogeny (from the Greek "onto", being and "genesis", origin, generation) is another field of biology which is in charge of studying the development of living beings throughout their individual lives, is say, studies how organisms and their maturation process are formed, both before and after birth.

Ontogeny recognizes different stages in the development of the organism, beginning with the fertilization of one reproductive cell with another, that is, the union between two gametes (in many species animals).

From the union arises a zygote, which is the result of the fertilized cell having undergone a process of mitosis, dividing into several cells and creating a blackberry-shaped structure. The next phase consists of embryogenesis, in which the zygote is segmented. Then organogenesis would come, in which organs and tissues are formed and an individual would already be more or less forming.

How they relate?

The concept of ontogeny and that of phylogeny are closely related. As we have said, ontogeny is responsible for studying the individual development of an organism, seeing which phases it goes through and which new structures, both anatomical and functional, acquiring. Phylogeny is responsible for the study of the evolution of the species and evolutionary relationshipsThis is their interspecific kinship, both with other modern species and with extinct species.

By studying ontogeny, and by focusing on embryos, scientists believe that evolutionary history can be learned. Although this does not always have to happen, it is quite frequent that, while observing an embryo of any species, ancestral characters are found that are conserved in the development of said organism.

An example of this is the embryo of different animals that, at first glance, do not seem to be related: chickens and humans. One would say that it is difficult to think that an animal that lays eggs, with feathers, beak, hollow bones and wings has some kind of kinship with humans. However, their embryos are very similar, presenting both indentations and arches in the neck, structures very similar to pharyngeal clefts and gill arches that can be found in fish.

This idea of ​​relating ontogeny and phylogeny is not new, although it should be noted that today it is used as proof that two or more species are phylogenetically related. For a long time, ontogeny was believed to be a sample of how each species develops during its evolution. Current science, however, has neglected this theory, despite recognizing certain links existing between ontogeny and the so-called phylogeny (which studies the evolution of a taxon of organisms).

Some scientists of the late nineteenth century, just after the publication of Darwin's work and the Haeckel's appearance, they saw that ontogeny could not only reveal things about evolutionary history, but that, what's more, believed that the embryonic development of the individual was a kind of representation, step by step, of that history. These scientists went so far as to affirm that ontogeny recapitulates phylogeny (theory of recapitulation), causing an organism to pass it through all the adult stages of its history evolutionary or phylogeny.

Although this idea could have its meaning, already at that same time there were many scientists who argued that evolution did not work in this way. It could not be that an embryo, because yes, was a representation of the evolutionary history of its species. If this were the case, for example, in human beings, at some point in ontogenetic development something similar to a reptile, a monkey or a Homo erectus would have to appear.

The recapitulation hypothesis was disproved and is not part of the synthetic theory, theory which considers that evolution occurs from integrating natural selection Darwinian with the hereditary biological components and random changes (mutations) that occur in the genes.

Bibliographic references:

• de Queiroz, K.; Gauthier, J. (1990). "Phylogeny as a Central Principle in Taxonomy: Phylogenetic Definitions of Taxon Names". Syst. Zool. (39): 307-322. doi 10.2307 / 2992353.
• Gould, S.J. (1977). Ontogeny and Phylogeny. Cambridge, Massachusetts: The Belknap Press of Harvard University Press
• Toren, C. (2002) "Comparison and ontogeny." Anthropology, by comparison: 187.