Phylogeny and ontogeny: what are they and how do they differ?

A summary of these concepts used in biology coined by Ernst Haeckel.

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

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

Nevertheless, 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 rightly so, given that, in essence, both describe the origin and the types of changes that occur in the complex idea that is life. Let's see it below.

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, greatly inspired by the work of Charles Darwin and who popularized the work of the English naturalist in Germany.who was greatly inspired by the work of Charles Darwin and who popularized the work of the English naturalist in German lands.

He used the word phylogeny to describe the historical and generic development of a species, i.e., how a species has changed over time.The word phylogeny describes 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 the individual development, i.e., the maturation of an organism.. Today both terms have more or less the same idea behind them, although, thanks mainly to advances in genetics and the development of technology such as X-rays, both Biological fields have been increasing their knowledge.

What is phylogeny?

Phylogeny (from the 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 them.

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. If similarities in these aspects are found in two or more species, it can be said that there must be some relationship between them, it can be said that there must be some genetic relationship or evolutionary similarity..

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

These trees, which are currently based on genetic studies, constitute the basis on which phylogenetic knowledge is based. They are scientific classifications that allow us to see how closely related different species are to each other, whether modern, past or extinct.They are scientific classifications that allow us to see how closely related different species are to each other, both modern, past and extinct, and to see how these relationships have been changing over the course of evolutionary history.

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

NameOrderFamilyGeneraDromedaryDromedaryArtiodactylaCamelidaeCamelusGinetaCarnivoraViverridaeGenettaWeaselCarnivoraMustelidaeMustelaNutriaCarnivoraMustelidaeLutra

It should 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, in a visual way, how the different modern species are related.

About human phylogeny

Human phylogeny is the study of the origin and development throughout evolutionary history of both modern humans (Homo spp.It is the study of the origin and development of both modern humans (Homo sapiens sapiens) and their predecessor or related hominid species, such as the Neanderthal.

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

Modern phylogenetics considers the following species and genera to be part of the human phylogenetic tree, based on the findings to date: Pliopithecus, Dryopithecus, Oreopithecus, Ramapitecus, Australopithecus, Paranthropus, advanced Australopithecus, Homo erectus, Homo erectus, Homo erectus, Homo erectus, Homo erectus, Homo erectus, Homo erectus, Homo erectus, Homo erectus and Homo erectus, 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 that is responsible for studying the development of living beings throughout their individual lives, ie, studies how organisms are formed, both before and after birth, and their maturation process..

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

From the union arises a zygotewhich 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 comes organogenesis, in which organs and tissues are formed and an individual is more or less formed.

How are they related?

The concept of ontogeny and phylogeny are closely related. As we have said, ontogeny is in charge of studying the individual development of an organism, seeing which phases it goes through and what new structures, both anatomical and functional, it acquires. Phylogeny deals with the study of the evolution of the species and its evolutionary relationships, i.e., its interspecific relatedness, both with other modern species and with extinct species.It is the study of the species' evolution and evolutionary relationships, that is, its interspecific relatedness, both with other modern species and with extinct species.

By studying ontogeny, and focusing on embryos, scientists believe that one can learn about evolutionary history. Although this need not always be the case, it is quite common, While observing an embryo of any given species, it is quite common to find ancestral traits that are preserved in the that are preserved in the development of that organism.

An example of this is the embryo of different animals that, at first sight, do not seem to be related: chickens and human beings. One would say that it is difficult to think that an egg-laying animal with feathers, beak, hollow bones and wings has any kinship with the human being. However, their embryos are very similar, both presenting clefts and arches in the neck, structures very similar to the pharyngeal clefts and gill arches that can be found in fish.

This idea of linking ontogeny and phylogeny is not new, although it is worth noting that today it is used as evidence that two or more species are phylogenetically related. For a long time, ontogeny was thought to show how each species develops during its evolution. Current science, however, has abandoned this theory, despite recognizing certain links between ontogeny and phylogeny (which studies the evolution of a taxon of organisms).

Some scientists at the end of the 19th century, just after the publication of Darwin's work and the appearance of Haeckel, saw that ontogeny could not only reveal things about evolutionary history, but, in addition, believed that the embryonic development of the individual was a kind of step-by-step representation of that history.. These scientists went so far as to claim that ontogeny recapitulates phylogeny (recapitulation theory), causing an organism to pass through all the adult stages of its evolutionary history or phylogeny.

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

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

Bibliographical 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.