Definition of Biological Evolution

A very remarkable recent finding is the discovery that some of our genes are the same as those of others. organisms unicellular This serves as evidence that all forms of life - including bacteria, plants, fungi and animals - share their ancestors. Biological evolution is one of the great unifying theories of Biology.

Historical background of evolution

By the mid-19th century, a growing number of biologists had concluded that current species evolved from earlier species. One of the first scientists to propose a mechanism for evolution was the French biologist Jean Baptiste Lamarck (1744-1829). In 1809, Lamarck hypothesized that organisms evolved through the inheritance of acquired characteristics, a process in which that the bodies of living organisms were modified by the use or lack of use of parts and these modifications were inherited to their offspring decendents. However, today it is known that evolutionary processes do not occur in this way.

In 1858, Charles Darwin (1809-1882) and Alfred Russel Wallace (1823-1913) independently shared evidence convincing evidence that it supported biological evolution and that it also explained the mechanism through which organisms they changed. Darwin proposed two main hypotheses: organisms have descended, with modification, from common ancestors; and the most important factor causing modification is natural selection, acting on the variation that can be inherited.

Darwin provided abundant information on descent with modification, since then various observations of geographic distribution, paleontology, embryology, genetics, molecular biology, comparative anatomy, paleontology and biochemistry have confirmed that all living organisms are related to each other in a history of common ancestry.

Determining factors to understand the concept

The word evolution is widely used as a synonym for change. However, it is important to note that the type of evolution we are talking about in this article is biological. The body of a triathlete who spends months in the Himalayas gets used to being at high altitude. Part of this is because the number of red blood cells, cells responsible for transporting oxygen, increase in number in response to the oxygen-deprived environment. The color change of the arctic fox's fur from brown to white in the winter, the color change of the skin of the human body when exposed to the sun are only changes that last one season a year. It is not about evolutionary changes. Changes in traits during an individual's life in response to the environment are not evidence that the individual has evolved, since such traits are not heritable.

For traits to be evolutionary they have to have the ability to be passed on to subsequent generations. Evolutionary changes occur at the population level, which is defined as a group of organisms of the same species that inhabit the same geographic area and a given time. Darwin noted that populations, not individuals, evolve, although he was unable to explain how these traits change over time. It is now known that the diversity of a population is a function of the genetic diversity of individuals within a population. Because genes and phenotypic traits are related, evolution involves genetic changes.

Natural selection and adaptation

Natural selection is survival and reproduction differential of different genotypes in a population, causing changes in the genetic frequencies of the populations. He is the natural "filter" of phenotypic traits in populations in a given environment. Evolution includes other processes besides natural selection, but this is the only one that results in adaptations.

Darwin and Wallace resulted in four observations on which the process of natural selection is based:

1. Organisms have variations that are inherited from generation to generation: Darwin emphasized that members of a population vary in their physical, behavioral, and functional characteristics. Furthermore, he pointed out that variation is essential for natural selection to operate. He thought there was a mechanism of inheritance, but he was never sure what it might be.

2. Organisms compete for available resources: Darwin, inspired by Malthus's postulates about the exponential growth of the human population vs. the linear growth of Resources He realized that if all the descendants of an animal population were to survive, the available resources would be insufficient to support the growing population. increase. He imagines that all human beings who have been born throughout history have survived to their death. adult stage and had reproduced, the lack of resources would be much greater than what we live currently.

3. Individuals within a population differ in reproductive success: Some individuals have favorable traits that help them compete in an environment with limited resources. Individuals with favorable traits for a given environment obtain more resources and increase their probability of survival than those with less favorable traits for that environment, which favors, what Dawin called, a differential reproductive success.

4. Species adapt to conditions as the environment changes: An adaptation is any evolutionary trait that causes an organism to thrive in a given environment. Adaptations are especially noticeable when unrelated organisms living in similar environments exhibit similar traits. Manatees, penguins, and sea turtles, for example, have flippers that help them move through the water. Adaptations to specific environments are the result of natural selection. The accumulation of adaptations results in new species.

Evidence of evolution

fossil record

Fossils are the remains and traces of past life or any other direct evidence of it. Traces include, for example, trails, footprints, burrows, droppings, and galleries of subterranean organisms. In general, the soft parts of an organism are not preserved because they are eaten by scavengers or are decomposed by microorganisms. Sometimes the organism is buried very quickly and, in this way, the decomposition never takes place. complete, or is completed slowly, so that the soft tissues leave an imprint on their structures. However, most of the fossil record is made up of the hard parts of organisms—such as bones, shells, or teeth—because they are generally not eaten or destroyed.

Biogeographic evidence

Darwin emphasized that in the case where the geography separates seas, islands and continents, a different mix of plants and animals was to be expected. For example, Darwin observed that there were no rabbits in South America, even though the environment was suitable for them to live there. In Earth's history, South America, Antarctica, and Australia were originally connected. Marsupials, mammals whose females have an external body bag where their young complete their development, evolved through oviparous mammalian ancestors. Currently marsupials are endemic to South America and Australia. The territory that is now Australia split off, resulting in a great diversification of marsupials. consequence of the little competition exerted by the placental mammals, whose young end their development within the maternal womb. The opposite process occurred in South America where placental mammals predominated, competition for marsupials was greater and, therefore, the diversification of the marsupials was less with respect to that which occurred in Australia.

anatomical evidence

The forelimbs of vertebrates are used in different ways, to fly, swim, run, climb, swing on tree branches. However, all limbs have the same number of bones organized in similar ways. Structures that are anatomically similar, because they are inherited from a common ancestor, are called homologous. On the other hand, the analogous structures have the same function, but they originated in the different groups independently.

vestigial structures

It is a reduced or incompletely developed structure that has no function or has a reduced function. Although vestigial structures appear to have no function, they can sometimes have new uses. Examples of vestigial structures are the wings of the ostrich, they no longer have the function of flight, but they give stability to the bird when it runs and this allows it to reach a greater speed, this shows that natural selection can give a different function to vestigial structures.

biochemical evidence

All living organisms use the same basic biochemical molecules, including DNA, RNA and ATP. From this we infer that the first living cells possessed these biomolecules and were the ones that gave rise to life as we know it. Furthermore, some amino acid sequences of some proteins they are similar throughout the tree of life.