LAMARCK'S THEORY OF EVOLUTION: ORIGIN, POSTULATES, EXAMPLES - BIOLOGY - 2024

The theory of Lamarck was the first coherent theory where it was proposed that organisms evolved. It focuses on the existence of a "vital force" within living beings that pushes them to modify certain physical features over time with a defined purpose.

This theory opened the doors to evolutionary thinking and was the predecessor of the theory of the evolution of species proposed by Darwin in the book The Origin of Species. However, it was harshly criticized, as there was not enough experiment or evidence to support it.

Larmack's theory or Lamarckism defends the idea that an organism can transmit characteristics that it has acquired during its life to its offspring. For example, giraffes that stretch their necks to reach eaten transmit this characteristic to their offspring.

Lamarck's theory of evolution was proposed in 1809 by the French naturalist Jean-Baptiste Pierre Antoine de Monet, better known today as "Lamarck", the name with which he signed his publications.

Lamarck was one of the fathers of paleontology and, in addition, he was the one who coined the term "Biology" to identify the science that studies living things.

At the historical moment in which Lamarck raised his concepts on evolution, creationist ideas predominated, that is, religious ideas about the origin of the universe through "Divine Creation."

His theory supported the idea of ​​the "spontaneous generation of life" and the search for perfection by living organisms. Lamarck was in favor of which the life of all the beings arose from the inorganic matter and, through a “breath of life”, a unique soul was given to each body.

Lamarck proposed that the change of species occurred with a "sense" or a "purpose" and considered that the more complex animals arose from simpler animals.

Origin of the theory

Portrait of Lamarck (Jean-Baptiste Pierre Antoine de Monet) (Source: Charles Thévenin via Wikimedia Commons)

Lamarck was born on August 1, 1744 in Paris. He devoted himself mainly to the observation and classification of plants and animals, carrying out important studies on typical French vegetation. In addition, he was one of the first to use the model of dichotomous keys proposed by Linnaeus for the classification of living beings.

Lamarck's theory was first published in the book "Zoological Philosophy" in 1809. There are no other Lamarck "notebooks" apart from this book that reveal or lead us through the thoughts that led the scientist to his conclusions regarding evolution.

In this book, Lamarck proposed that the organs of animals "evolve" or are modified according to a kind of "norm" of use and disuse, depending on physiological needs and the environment where they are found.

Therefore, a drastic change in certain environmental conditions can "activate" behaviors that could lead to the acquisition of new organs that, over time, would significantly change organisms and their life cycles.

For other scientists of the time, his theory was based on very few observations and a lot of speculation (things that he expected to be so). However, Lamarck was a great scholar and was well acquainted with the works of Descartes, Leibniz, and Newton, to name a few.

Postulates

Lamarck mixed the findings of his taxonomic observations with his philosophical thoughts and thought that the organisms we observe today are the most complex and advanced versions of simpler ancestor organisms.

Thus, Lamarck described evolution as a progressive and continuous process, where nature produces increasingly complex and perfect beings from simple organisms that arise rapidly by spontaneous generation.

Lamarck's postulates can be summarized in two central ideas:

1. Frequent and continuous use of an organ develops it in proportion to the duration of its use, while lack of use gradually weakens it until it disappears.
2. The characteristics or organs that individuals acquire or lose due to certain circumstances (use or lack of use) are preserved in their children (descendants) through reproduction, provided that these changes are acquired by both parents (parental).

Some additional ideas to these postulates, although of less relevance, are:

- Life originates spontaneously, using as a “substrate” bodies that have been modeled from inorganic materials.

- All living organisms have an internal impulse that "pushes" them towards perfection, in the French literature of the time they refer to this as "élan vital".

- The path to the perfection of each organism is a linear and progressive process that, in animals, occurs to finally achieve the human form.

- There are some alternate paths in that evolutionary linearity, where some organisms stop or deviate, so that different forms can be observed at the same time.

Examples

Giraffes

Evolution according to Lamarck (Source: Solarist via Wikimedia Commons)

The most famous example of Lamarckism is the drawing of a giraffe with a short neck that tries to reach, without success, the leaves of a high branch of a tree and, next to it, another drawing where a giraffe, related to the first but many generations later, he manages to reach the leaves of said tree by stretching his neck.

Kangaroos

Lamarck also referred to the legs of kangaroos as an example of the development of the organs he was referring to. As the kangaroo constantly used its legs to move, these limbs were overdeveloped in the animal.

Ostriches

Other examples included the upper limbs of ostriches (the wings) as an example of stunted limbs, in contrast to highly developed legs, practically specialized for running at high speeds.

Moose

The hardness of elk horns was an example widely publicized by Lamarck, who showed males with highly developed antlers, hard, resistant and of great size, in obvious contrast to the antlers of female moose, which did not need for fights.

Hominid ancestors

As an amateur paleontologist, Lamarck relied on the fossils of our hominin ancestors to claim that humans were the culmination of the complexity of monkeys.

Elephants

The nose of elephants was also used by Lamarck as a strong example to defend his theory, since when observing drawings of the ancestors of elephants, the change of the trunk could be appreciated, both in size and in strength and texture.

Neo-Lamarckism

Many authors are of the opinion that the image of Lamarck has been unfairly judged and diminished since, if the ideas that predominated in his time are taken into consideration, his works could be considered rather as “avant-garde”.

In this way arose a current of thought known as “Neo-Lamarckism”, where the defenders of Lamarck's theories rescued many of his ideas and proposals. Nonetheless, "neo-Lamarckist" scientists continue to face the difficulty of testing Lamarck's hypotheses and predictions.

The case of John Cairns

Lamarck's central proposal implies that organisms evolve in a directional way, that is, with a purpose or towards a "goal", in response to circumstances of the environment that surrounds them.

Despite the fact that modern evolutionists (Darwinists) consider evolution to be a completely random process, molecular biologist John Cairns made one of the few experimental findings on which neo-Lamarckism relies.

Cairns inoculated a strain of E. coli (a bacterium present in the intestinal flora of humans) unable to digest lactose in a medium where lactose was the only available sugar, hoping that, as the cells divided, it would appear (at random) a mutation such as to allow individuals of successive generations to use lactose as a nutrient.

To Cairns' surprise, bacteria in the presence of lactose went into a period of starvation (stopped eating) so they did not reproduce. Furthermore, within a short time, mutant bacteria appeared within the colonies, capable of digesting lactose, as if the bacteria in the colony had divided at least 100 times.

All of these observations appeared only when lactose was added to a medium in which the bacteria had been deprived of nutrients for several days, suggesting that the mutations occurred in response to the presence of lactose and not randomly, as might be expected.

Molecular foundations of Neo-Lamarckism

At present, molecular mechanisms such as epigenetics and microRNas (miRNAs) have been found that can influence and direct in a certain way and through offspring, evolutionary changes in living organisms as a function of environmental changes.

One of the main mechanisms of epigenetic regulation is exerted through histone proteins, which directly influence the expression of genes that code for the traits of individuals.

These proteins are able to expose or hide, as necessary, the DNA fragments where the genes are so that they are read (or not) inside the cells. These regulatory patterns and the way in which histones are found in each cell can be inherited from parents to children.

MicroRNas (miRNAs) are small single-band nucleic acids found within cells and are responsible for regulating many of the processes involved with gene expression.

Many authors consider that miRNAs are a kind of "vehicles" that parents use to transmit information about the environment to their offspring.

Despite these "molecular bases" on which neo-Lamarckists rely, this remains a highly controversial topic and has attracted the attention of many researchers, both geneticists and evolutionary scholars, since it touches on sensitive aspects of this field. of scientific research.

References

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