For centuries, the question of how different forms of life could have emerged has fascinated humanity. Myths and legends have been created around this question, but more complete and systematic theories have also been developed .

Lamarck’s theory is one of the most famous attempts to propose an idea of the evolution of species in which there is no divine intelligence to direct the process.

Who was Lamarck?

The person who proposed what we know today as Lamarck’s theory was Jean-Baptiste de Lamarck , a French naturalist born in 1744. In his time, the study of living beings was a totally different discipline from what biology is today, and that is why he held ideas regarding the functioning of natural processes in which the divine intervened, something that would be scandalous by today’s scientific standards.

Lamarck made biology largely independent of religion by proposing a theory of evolution in which the intelligences of the beyond had no role .

What was Lamarckism?

Before the English naturalist Charles Darwin proposed the theory of evolution that would change the world of biology forever, Lamarck’s theory already proposed an explanation about how different forms of life could have appeared without the need to resort to one or several gods.

His idea was that while the origin of all forms of life could be created spontaneously (presumably by direct act of God) but that, after that, evolution was taking place as a product of a mechanical process resulting from the physical and chemical properties of the matter with which organisms and their environment are formed.

The basic idea of Lamarck’s theory was as follows: the environment changes, life forms struggle to continually adapt to the new demands of their habitat , these efforts modify their bodies physically, and these physical changes are inherited by the offspring. That is to say, that the evolution proposed by Lamarck’s theory was a process sustained by a concept called inheritance of acquired characteristics : parents transmit to their children the traits they acquire from how they relate to the environment.

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We know how this hypothetical process worked using the most famous example of Lamarck’s theory: the case of giraffes that stretch their necks.

The example of giraffes and Lamarck

At first, an antelope-like animal sees its environment become increasingly dry, so that grass and shrubs become scarce and it needs to resort to feeding on the leaves of trees more often. This makes stretching the neck one of the defining day-to-day habits of some members of its species.

Thus, according to Lamarck’s theory, pseudo-antilopes who do not fight for access to the leaves of trees by stretching their necks tend to die leaving few or no offspring, while those who stretch their necks not only survive since having their necks stretched is prolonged, but this physical characteristic (the longer neck) is transmitted to their inheritance.

In this way, with the passage of time and generations, a form of life appears that did not exist before: the giraffe .

From simplicity to complexity

If we move from the foreground of describing the process by which one generation passes on its acquired characteristics to the next, we will see that the explanation for which Lamarck’s theory tries to account for species diversity is quite similar to the ideas of Charles Darwin.

Lamarck believed that the origin of species was embodied in a very simple form of life that generation after generation gave way to more complex organisms. These late species carry the traces of the adaptive efforts of their ancestors , thus the forms in which they could adapt to new situations are more diverse and give way to a greater variety of life forms.

What is wrong with Lamarck’s theory?

If Lamarck’s theory is considered an outdated model it is, first of all, because it is known today that individuals have a limited margin of possibilities when it comes to modifying their body with its use. For example, necks do not lengthen simply by stretching, and the same is true for legs, arms, etc.

In other words, the fact that certain strategies and body parts are used a lot does not make them adapt their morphology to improve the fulfilment of this function, with some exceptions.

The second reason why Lamarckism fails is because of its assumptions about the inheritance of acquired capabilities. Those physical modifications that do depend on the use of certain organs, such as the degree of arm musculature , are not automatically transmitted to the offspring , since what we do does not modify the DNA of the germ cells whose genes are transmitted during reproduction.

Although it has been proven that some forms of life transmit their genetic codes to others through a process known as horizontal gene transfer, this form of modification of the genetic code is not the same as that described in Lamarck’s theory (among other things because the existence of genes was not known at the time).

In addition, a type of gene has recently been discovered whose function is to restart the epigenome of the life forms being created in their zygote phase , that is, to ensure that there are no acquired changes that can be inherited by the offspring.

The differences with Darwin

Charles Darwin also tried to explain the mechanisms of biological evolution, but unlike Lamarck he did not simply place the inheritance of acquired traits at the centre of this process.

Instead, he theorized about the way in which the pressures and demands of the environment and of the forms of life that coexist among them cause, in the long run, certain features to be passed on to the offspring with a greater frequency than others , which in the course of time would cause a good part of the individuals of the species, or even almost all of them, to end up possessing that characteristic.

Thus, the progressive accumulation of these changes would cause different species to be created over time.

The merits of Lamarckism

The fact that this naturalist rejected the idea that miracles have an important role in the creation of all species meant that Lamarck’s theory of evolution was ignored or disregarded until the time of his death. In spite of this Lamarck is today widely recognized and admired not because his theory was correct and served to explain the process of evolution, since Lamarck’s theory has become obsolete, but for two different reasons.

The first is that Lamarck’s understanding of evolution can be interpreted as an intermediate step between classical creationism, according to which all species have been directly created by God and remain the same through generations, and Darwin’s theory, which is the basis of the theory of evolution that is the current foundation of the science of biology.

The second is simply the recognition of the difficulties this naturalist had to face in devising and defending the Lamarckist theory of evolution in its historical context at a time when the fossil record of life forms was scarce and chaotically classified. Studying something as complex as biological evolution is no easy task, because this requires analyzing very concrete aspects of life forms in detail and building from this a highly abstract theory which explains the kind of natural law that is behind all these kinds of changes.