Evolutionary theories are all those that have been raised by the great thinkers of humanity in the course of history to provide plausible explanations for the evolution of living beings on Earth.
Since the beginning of human societies, man has asked himself where living beings come from and where they come from; therefore, evolution has been the subject of intense debate for many centuries, heavily influenced by philosophical and religious beliefs. and, more recently, scientific.
However, as a current of scientific thought, evolutionism was probably born with the theories of Charles Darwin (1809-82), an English scientist who dedicated an important part of his life to the study of the effects of “natural selection” and “Adaptations”. ” about species.
What is evolution?
Evolution is the biological process by which species in the biosphere (whatever their type) originate, diversify, and become extinct. Through fossil evidence, evolution seeks to explain the changes and transformations that different species undergo throughout their history.
As Darwin set a revolutionary precedent in the scientific world (he is considered the “father of evolutionism”), today we list evolutionary theories as “pre-Darwinist” and Darwinian, suggesting the historical and scientific context in which these were formulated.
Below are different theories of evolution.
There were many “pre-Darwinian” thinkers who, in their time, dedicated themselves to the study of living beings and the search for answers to the multiple questions related to their evolution.
you are reading theories of evolution.
– Aristotle and the immutability of organisms
Aristotle (384-322 BC) was perhaps one of the first thinkers to implement a hierarchical system of classification for living things.
This insisted on the “immutability” and eternal perfection of the species, as well as on the existence of a progressive, that is, ascending, hierarchical order, at whose “peak” man was.
Aristotle stated that the order thus proposed responded to a “vital force” and that there was nothing that led to fundamental changes in individuals, hence the theory of immutability, that is, of living beings created and not prone to change.
– James Ussher and the day of creation
Other great philosophers began to investigate life and the human being as a fabulous spectator. The acceptance of theories about biological evolution slowly penetrated society, with the religious being its main detractors.
Today religion is not entirely closed to discussion, but in the past many popular creationist thinkers have tried to reinforce the version of the origin of the universe, the earth and living beings in the hands of a “creator” of a higher nature, to exclude any atheistic thinking.
Among them was the Irish Anglican Archbishop James Ussher (1581-1656) who, from an analysis of biblical texts, deduced that the creation took place on an exact date: October 23, 4004 BC.
His statements, therefore, proposed that the Earth was no more than 6,000 years old and that God created infinite creatures, each “surpassing” the next (both simple and complex forms), including human beings as we know them today, that is, immutable.
The strong influence of religion on scientific thought was evident until the 19th century.
This is demonstrated in history by the fact that thinkers of the late 17th and early 18th centuries were clearly devoted to the description of plants and animals and not to any attempt to explain how they acquired their characteristics and forms.
Carolus Linnaeus (1707-78), for example, was a naturalist (botanist) who devoted immense efforts to describing nature, apparently “revealing” the unchanging order of life that had been created by God.
– Georges-Louis Leclerc and spontaneous generation
Also known as “the Count of Buffon”, Leclerc (1707-88) favored the idea of the origin of life through spontaneous generation and the existence of a “master plan” inherent in nature.
In a way, he refuted the Aristotelian conception of immutability, as he went so far as to propose that species had the capacity to change over time, perhaps due to the influence of the environment or mere chance.
Furthermore, as part of his speculations, Leclerc proposed that the Earth was at least 75,000 years old and even suggested in his notes that man and apes were somehow related.
– Jean-Baptiste Lamarck and the theory of acquired characters
Perhaps the first true pre-Darwinian evolutionist was Lamarck (1744-1829), a French naturalist who published an evolutionary theory generated from observations of invertebrate fossils deposited at the Natural History Museum in Paris.
According to this character, all organisms had an “internal progressive tendency” that forced them to “go up” in the natural scale, that is, that living beings actually changed over time, always tending to an “improved version of themselves”. themselves”. .
More specifically, Lamarck proposed that if an organism (his examples were based on animals) had not yet reached the “peak” of its development, the consecutive use of any organ could give it a “potency” proportional to the duration of that use, and otherwise, disuse made it disappear.
In short, Lamarck established that, for example, if a giraffe could not reach the highest leaves on a tree branch, its neck would gradually increase and these small changes due to use would be passed on to the next generation and then to the next and so on. onwards, until one of the individuals managed to reach that food.
– Georges Cuvier and the theory of catastrophism
Soon after Lamarck released his theories, some scientists went to great lengths to discredit them. Among them was George Cuvier (1769-1832), a French naturalist who was the first to document the extinction of ancient animals (he was an expert on dinosaurs).
His ideas were summarized in the doctrine of catastrophism, in which evolution was explained through violent catastrophes (floods, mountain formations, etc.) that caused the loss of numerous species and the development of new ones.
With this theory, Cuvier and the other adherents sought to explain the abrupt differences between fossil records and the sudden changes that were noticed in extinct species.
– Charles Lyell and uniformitarianism
Cuvier’s catastrophism was refuted by Lyell (1797-1875), who proposed an evolutionary theory known as uniformitarianism, according to which the evolution of species was strongly influenced by slow, gradual changes that occurred from the beginning of time on the Earth’s surface and that are imperceptible to the human eye.
– Alfred Russell Wallace and natural selection
Wallace (1823-1913) was a British naturalist who, around 1858, reached the same conclusions as Darwin, explaining the evolution of species thanks to natural selection.
Since Wallace and Darwin made their findings public to the Linnean Society of London at the same time, many authors believe that the theory of natural selection should actually be known as the Darwin-Wallace theory.
Charles Darwin and natural selection
As the “father of evolutionism”, Darwin was the first of all naturalists until the mid-1800s to establish a relationship between evolutionary thinking (usually only conceptual) and the “real world”.
This means that Darwin demonstrated with facts (gathered and explained in The Origin of Species ) the process of evolution by natural selection and adaptation.
According to his theory, natural selection allows individuals with the most favorable characters to survive in a given environment and, in addition, to reproduce more, passing these characters on to their children (survival of the fittest).
Consistent with this, Darwin also proposed that nature produces more individuals than is “necessary” for each species in order to allow natural selection to take place.
Thus, the survival of the fittest is nothing more than a result of the “nature preservation instinct” itself, to ensure that only the best adapted individuals survive and spread in the changing environment.
Darwin also proposed that the new species observed are the product of the accumulation of successive small changes (gradualism), produced by different types of adaptations.
The post-Darwinian era
Darwinian theories of evolution had a lot of support in the scientific community, as did Mendelian theories of character inheritance and chromosomal inheritance theory later on.
However, for many years these approaches seemed “divorced” or “incompatible”, until the emergence of the synthetic theory of evolution, also known as modern synthesis or neo-Darwinism.
Thanks to the contributions of scientists such as S. Wright, J. Haldane, R. Fisher and T. Dobzhansky, this theory now has the molecular basis to explain the effect of natural selection on the variability of species (of their populations) or rather on the frequencies alleles of a population.
We hope that you have grasped the theories of evolution.