Phylogeny And Ontogeny: What They Are And How They Differ

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

Phylogeny and ontogeny

Phylogeny and ontogeny are two words that usually 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 is the origin and what types of changes occur in that idea so complex that is to life. Let’s see it next.

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. Today both terms have more or less the same idea behind, although, and 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 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 They populate the planet, in addition to developing 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. 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 similarity.

There are species that can 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 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 us to see how closely different species are related, both modern and past and extinct, and see how these relationships have changed throughout the evolutionary history.

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 the different modern species are related.

On human phylogeny

Human phylogeny is the study of the 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 modern prosimians, the monkeys of the New and Old World, the gibbon, the orangutan, the chimpanzee and the gorillas.

Modern phylogenetics considers that the following species and genera are part of the human phylogenetic tree, based on the findings to date: Pliopithecus, Dryopithecus, Oreopithecus, Ramapitecus, Australopithecus, Paranthropus, advanced Australopithecus, Homo erectus , Homo erectus soloensis , Homo neanderthalensis , Homo rhoesiensis , and 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, that is, it studies how they they form, both before and after birth, the organisms and their maturation process.

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 animal species).

A zygote arises from the union, which is the result of the fertilized cell having carried out 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 one would already have an individual more or less forming.

How they relate?

The concept of ontogeny and 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 what new structures, both anatomical and functional, it acquires. Phylogeny is responsible for the study of the evolution of the species and evolutionary relationships, this is its interspecific kinship, both with other modern species and with extinct species.

By studying ontogeny, and 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 any kind of kinship with humans. However, their embryos are very similar, presenting both indentations and arches in the neck, structures very similar to the pharyngeal fissures 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 nowadays 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 put this theory aside, despite recognizing certain links between ontogeny and the so-called phylogeny (which studies the evolution of a taxon of organisms).

Some scientists in the late 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 also believed that the embryonic development of the individual was a kind of representation, step by step, of that story. These scientists went so far as to affirm that ontogeny recapitulates phylogeny (recapitulation theory), making an organism pass through all the adult stages of its evolutionary history or phylogeny.

Although this idea could make sense, 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 humans, 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 refuted and is not part of the synthetic theory, a theory which considers that evolution occurs from integrating Darwinian natural selection with hereditary biological components and random changes (mutations) that occur in 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, SJ (1977). Ontogeny and Phylogeny. Cambridge, Massachusetts: The Belknap Press of Harvard University Press
  • Toren, C. (2002) “Comparison and ontogeny.” Anthropology, by comparison: 187.

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