The theory of biological evolution
The man is a curious being that throughout history has questioned everything that surrounds him and has been inventing the most diverse ideas to explain it.
It is not surprising that our ancestors also wondered about the animals and plants they saw around: were they always like this or have they changed over time? And if there were differences, What are the mechanisms that have been used to carry out these modifications?
These are the main unknowns that have been tried to solve through what we know today as the theory of biological evolution, which is at the base of biology and communicates with a good part of the realm of psychology, when talking about the origin of certain innate tendencies that could be influencing our behavior and our way of thinking. Let's see what it consists of.
Evolution of a theory
Until the nineteenth century, the predominant idea about the origin of the species was creationism. According to this doctrine, an all-powerful entity had created each of the existing living beings, and these had not changed over time. But at this time, alternative theories began to emerge.
The most remarkable was the proposal by Jean-Baptiste Lamarck ; this French naturalist proposed that all species had the will to change and the ability to transfer to their offspring these changes acquired through their actions, a mechanism of transmission of characteristics known as inheritance of acquired characters.
Lamarck, in opposition to the creationists, defended the idea of the evolution of the species, but it accepted that the species generated of spontaneous form and did not have a common origin. I will not go longer, since you have a very complete article about Lamarckismo in this same link:
- You can see it here: "The Lamarck Theory and the evolution of the species"
Charles Darwin enters the scene
A big step had been taken in admitting the idea of biological evolution, but Lamarck's theory had many fissures. It was not until 1895 when the British naturalist Charles Darwin published the book The Origin of Species, in which proposed a new theory of evolution (which would be known as Darwinism) and a mechanism for it: natural selection . Along with the also British naturalist Alfred Russel Wallace, Darwin exposed new ideas in favor of evolution.
According to Darwin, all species come from a common origin, from which it was diversified thanks to natural selection . This evolutionary mechanism can be summarized in that the species better adapted to the environment that surrounds them, reproduce and have offspring that, in turn, are more likely to reproduce successfully, giving way to new generations. The English naturalist also accepted the idea of extinction, which was the other side of the coin: species less adapted to the environment tended to reproduce less and less, in many cases disappearing.
Thus, first appeared on the scene populations of living beings with different characteristics, and the environment exerted a pressure on it that made some of them had more reproductive success than others, making their characteristics spread and making others disappear. What characterized this process was its natural character, oblivious to the influence of a supernatural entity to direct it; It happened automatically, in the same way that a snowball is made bigger by the influence of the force of gravity applied on the side of a mountain.
Neo-Darwinism
Despite removing the divinity in creation and explaining a basic mechanism by which species are changing and diversifying over time, Darwin was unaware of the term we now know as genetic variability, and did not know the existence of genes. That is, he did not know how the variability of characteristics appeared on which the pressure of natural selection acts. Therefore, he never completely rejected the idea of the inheritance of acquired characters proposed by Lamarck.
Unlike Darwin, Wallace never accepted this idea, and from this dispute appeared a new evolutionary theory called Neo-Darwinism , driven by the naturalist George John Romanes, who in addition to reject Lamarckian ideas in their entirety, believed that the only evolutionary mechanism was natural selection, something that Darwin never held. It was not until the early twentieth century when Mendel's laws were accepted, showing that mutations in DNA are pre-adaptive, that is, first a mutation is suffered and then put to the test if the individual in whom it has been given it is better adapted for the medium or not, breaking the idea of the inheritance of the acquired characters.
With this premise, the geneticists Fisher, Haldane and Wright gave a new twist to Darwinism. They integrated the theory of the evolution of species through natural selection and genetic inheritance proposed by Gregor Mendel, all with a mathematical basis. And this is the birth of the theory currently accepted by the scientific community, known as the synthetic theory. Is proposes that evolution is a more or less gradual and continuous change explained through genetic variability and natural selection.
The social impact of the theory of evolution
The biggest problem that Darwin had was to dispense the figure of the hand of God in his theory on what could be the explanatory mechanism of biological diversity, something unforgivable at a time when religion and creationism were hegemonic.
But nevertheless, The theoretical legacy of Charles Darwin was robust, and over the years the emergence of new fossils gave a good empirical support to his theory ... which did not make his contribution to science from a religious perspective. Even today environments closely linked to tradition and religion deny the theory of evolution, or consider it "simply a theory", implying that creationism enjoys the same scientific endorsements. Which is a mistake.
Evolution is a fact
Although we speak like the theory of evolution, it's actually a fact, and there is evidence to not doubt its existence . What is discussed is how should be the scientific theory that explains the evolution of the species of which there is evidence, does not question that process itself.
Below you can find several of the tests that demonstrate the existence of biological evolution.
1. Fossil record
Paleontology, the discipline that studies fossils, has shown that geological phenomena take a long time to complete, such as fossilization. Many fossils are very different from the current species, but at the same time, they have a certain similarity. It sounds weird but with an example it will be easier to understand.
The Glyptodon was a Pleistocene mammal that bears a striking resemblance to a current armadillo but in a giant version: it is a trace of the evolutionary tree that leads to the current armadillos . The same fossils are also proof of extinction, since they show that in the past there were organisms that today are no longer among us. The most emblematic example are the dinosaurs.
2. Imperfect vestiges and designs
Some living beings have designs that we could say are imperfect. For example, penguins and ostriches have hollow wings and bones, but can not fly. The same goes for the whale and the snake, which have pelvis and femur, but do not walk. Is The organs are known as vestiges, organs that were useful to an ancestor but now have no use .
This is another proof of the evolution that, in addition, reveals that this process is opportunistic, since it takes advantage of what is at hand to organize a new organism. The species of life are not the result of an intelligent and well-planned design, but are based on functional "sloppiness" that are being perfected (or not) with the passage of generations.
3. Homologies and analogies
When you compare the anatomy between different organisms, we can find cases that, once again, are proof of evolution . Some of them are consist of homologies, in which two or more species present a similar structure in some of the parts of their anatomy, but they are to exercise different functions, which is explained because they come from the same ancestor. Examples are the extremities of the tetrapods, as they all have a similar structural arrangement despite the fact that their limbs have different functions (walking, flying, swimming, jumping, etc.).
The other case is the analogies, organs of different species that do not have the same anatomy but share a function. A clear example are the wings of birds, those of insects and those of flying mammals. They have been developed by different ways to reach the same function, that of flying.
4. DNA sequencing
Finally, the genetic code, with some exceptions, is universal, that is, every organism uses the same. If it were not, it would not be possible for E.coli bacteria to produce human insulin by introducing the gene (of human origin) responsible for generating this substance, as we do today. In addition, transgenics are another evidence that the genetic material of all life forms has the same nature. OR evidence that all species have a common origin and evidence of evolution .
Evolutionary mechanisms
Although we have talked about natural selection as a mechanism that uses evolution to advance, it is not the only one that is known. Here we will see the different types of selection that influence evolution .
1. Natural selection
In the theory of biological evolution born with Darwin, this naturalist originated the idea of natural selection from his observations on the voyage of the Beagle during his voyage through the Galapagos Islands. In them, it struck him that each island had its own species of finch, but all had a resemblance between them and those found in the neighboring continent, South America.
The conclusion reached is that the finches of the islands originally came from the continent, and that upon reaching each island suffered an "adaptive radiation", in this case by food, thus generating a range of variants from the same group of ancestors; thus, these birds have very different peaks, having adapted to the ecosystem of each island separately .
Today we can clarify better the functioning of natural selection. The environment is not stable and changes over time. The species undergo mutations in their genome at random, and these make them change their characteristics. This change can favor their survival or, on the contrary, it can make their life difficult and cause them to die without offspring.
2. Artificial selection
It is not properly an evolutionary mechanism, but a variety of natural selection . It is said to be artificial, since it is the human being who directs the evolution for his own interests. We speak of a practice that has occurred in agriculture and livestock for millennia, choosing and crossing plants and animals for greater productivity and performance. It also applies to domestic animals, such as dogs, where other characteristics were sought, such as more strength or more beauty.
3. Genetic drift
Before talking about this mechanism, you have to know the allele concept. An allele consists of all the mutational forms of a particular gene. To give an example, the different genes of eye color in man. Genetic drift is defined as a random change of the allelic frequency from one generation to another, that is, the environment does not act. This effect is best seen when the population is small, such as inbreeding , where genetic variability is reduced.
This mechanism can eliminate or fix characteristics in a random way, without the need for the environment to act in its selection. And therefore, in small populations, it is easier to lose or gain a quality by chance.
Controversy related to evolution
As we have seen, the theory of evolution currently accepted is synthetic theory (also known as modern synthesis), although there are alternatives that are against it because it is considered to contain certain shortcomings or concepts that are not explained or are not included.
1. Neutralism
Until not long ago, it was thought that there were only harmful mutations (negative selection) and beneficial mutations (positive selection). But the Japanese biologist Motoo Kimura said that at the molecular level there are many mutations that are neutral, that are not subject to any selection and whose dynamics depends on the mutation rate and the genetic drift that eliminates them, creating a balance.
From this idea was born an idea opposed to the one proposed by the synthetic theory, where Beneficial mutations are common. This idea is neutralism . This branch proposes that neutral mutations are common, and the beneficial ones are the minority.
2. Neolamarckismo
Neolamarckism is the part of the scientific community that still maintains that Lamarck's theory and its inheritance of acquired characters can not be ruled out. From there it is tried to reconcile this idea with the genetics, affirming that the mutations are not at random but that it is the consequence of the "effort" of the species to adapt to the environment. But nevertheless, its empirical basis can not be compared to that of the synthetic theory .
