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4.3.2. Darwin and Wallace

Darwin and Wallace's theory of evolution

Charles Darwin , after making a five-year scientific expedition around the world, and carefully observing the flora and fauna of the places he visited, developed a theory about the origin of species and their evolution, the theory of the natural selection.

Alfred Russel Wallace independently reached the same conclusions as Darwin. Although fame has gone to Darwin, both presented their findings jointly to the Linnean Society in London, on July 1, 1858.

The theory of the evolution of species by natural selection or Darwinism can be summarized in these points:

  • Existence of heritable variability. Individuals of the same species have small differences or variations between them, such as coloration, size, ability to obtain food, etc. These characteristics can be passed on to the offspring. The natural selection acts on this variability of individuals in a population.
  • Offspring with modification. The descendant individuals are not the same as the parents, since they inherit the characteristics of both parents and the descendants are different from them.
  • Differential reproduction. Organisms tend to reproduce by having as many descendants as possible, depending on the resources of the environment. A struggle for survival is established, competing with individuals from the same population for resources. Those organisms that have more advantageous characteristics will be able to survive better and have a greater probability that these characteristics will be transmitted to their offspring. Therefore, some agencies are more successful than others. Individuals with less favorable characteristics for a certain environment will have more difficulties living and having offspring.
  • The species changes. If the environmental conditions are maintained, the favorable variations will be more and more abundant, since they are transmitted from generation to generation. The less favorable variations will have less reproductive success and it will be more difficult for them to have offspring, and therefore, that variation will disappear. In this way, the species changes continuously and gradually.

The theories of Darwin and Wallace improved Lamarckist ideas, since they rejected the inheritance of acquired characters and introduced new concepts such as:

  • Population variability. Among the members of a population of a given species there is a great variety of different individuals. Each of them, due to their differences, is better adapted to a certain environment than to another. Therefore, some are better adapted than others to the environmental conditions and may have more offspring, which possibly have this beneficial characteristic. For example, a species of bear that has short hair because it lives in a warm place but in which there are also individuals with long hair. Having long hair is a disadvantage because they are too hot. But if the environmental conditions change, and the environment becomes colder, having long hair will become an advantageous quality compared to other individuals with short hair. Then, the hair ones will be the best adapted,Those that will have the best chance of surviving and leaving offspring, while those with short hair will gradually disappear. The natural selection allows the best adapted to survive and the worst adapted tend to disappear.
  • Sexual selection. Some individuals show characteristics that apparently do not improve their survival and even impair their survival, but instead have an easier time reproducing and passing their genes on to their descendants. For example, the feathers of peacocks that benefit you in courtship but make them more vulnerable. Reroduction, therefore, does not only depend on the ability to survive, but on the ability to call the attention of a partner or struggles between males to copulate with the female.
  • Natural selection. Natural selection, aided by the changes produced bygenetic mutations, causes gradual changes to occur in the individuals of a population that give rise to the appearance of new species. They are responsible for biological evolution. The descendants are not exact replicas of their parents, since two gametes are involved in sexual reproduction and the descendants inherit characteristics from both parents.
  • Coevolution. Some species are so interrelated that changes in one affect the other. For example, the relationship between predators and prey. Another example may be the Angraecum sesquipedales orchid (Darwin's orchid, Madagascar star, Christmas orchid or star of Bethlehem), it has nectar at the bottom of a tube almost 30 centimeters long, so Darwin assumed that there should be a pollinating insect with a proboscis (tongue) long enough to allow it to drink that nectar. Later a moth was found, Xanthopan morganii preadicta, with this characteristic, which is responsible for its fertilization.

Examples of Darwinism

It must be borne in mind that when Darwin and Wallace presented their theory, they were unaware of Mendel's work on the inheritance of characters. That is why they could not explain why such a variety of individuals existed or why there were some traits that were inherited.

Giraffe evolution

The giraffes' predecessors had necks of varying lengths. Environmental conditions made those with shorter necks more difficult to survive and have offspring. The long-necked ones, on the other hand, had an advantage over the others, they reproduced more easily and the offspring had long necks. Over the years, giraffes appeared, all with long necks.