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Natural selection

The steps of natural selection

 Automatic translation  Automatic translation Updated June 01, 2013

Natural selection is the process that leads to the appearance of species.
It helps in part to answer fundamental questions of man: who are we? Where we come from? Where are we going?
Alfred Russel Wallace and Charles Darwin proposed several steps to natural selection and "survival of the fittest."
Step 1: each generation of a species, too many individuals are born so that environmental resources can meet all their needs.
Step 2: it is established then inevitable competition between individuals for access to resources. As all individuals are different from each other, they discuss the competition with various advantages and disadvantages. Only individuals with more favorable characteristics about the difficulties survive. That is natural selection.
Step 3: If the characters are hereditary advantage, then they are forwarded to the next generation.


In 1798, Thomas Malthus note that living species tend to have exponential growth, so that resources can grow together. It concludes that a demographic catastrophe is inevitable.
Malthusian disasters have already been observed and studied in animal populations. In 1944, 29 reindeer were introduced to the island of St. Matthew, off Alaska's Bering Sea.
Food resources were abundant and the reindeer had no predators, the population exploded, reaching 6,000 individuals in the summer of 1963, representing growth of 30% per year.
A few months after the peak population, the population of deer declined and there remained only 42 female reindeer died of starvation because the vegetation had been severely and permanently degraded.

NB: the steps of natural selection are taken from the book "The Origins of Man" Pascal Picq.

 a population of reindeer

Image: living species tend to have an exponential growth when resources can not grow at the same rate.

A drawback becomes an advantage


The peppered moth is a moth that occurs in two forms, a light colored morph said typica and the other dark or melanic carbonaria said.
These moths arise during the day on trees.
In England before the industrial revolution of the 19th century was characterized by the transition from an agrarian society to an industrial society, populations of moths were primarily made of birch-colored individuals who relied on the trunks of pale, on which they arose.
With pollution due to industrialization, the trunks of trees were blackened and butterflies quickly became clear easy prey for birds.


Regarding the black butterflies, the disadvantage of color had become a major advantage in this new environment.
Spared by predators, they became the majority. The phenomenon is reversed again in the 1960s, when Great Britain made efforts to reduce air pollution.

Image: the peppered moth (Biston betularia L.) is an insect of the order Lepidoptera, family Geometridae. Here, two butterflies and dark colored. Butterflies are clear easy prey for birds. Credit: David Fox / Oxford Scientific Films and The work of the group of B. Kettlewell.

 Peppered moth

Between Lamarck and Darwin


The concept of evolution of species was proposed by Jean-Baptiste Lamarck in 1809.
Based on the observation of the physiological characteristics of organisms, it offers continuity of the living world, ranging from the simplest to most complex, and posits the existence of a relationship between all species. This relationship has its origin in the phenomenon of new species, or speciation: a species gradually accumulate new characters and eventually becomes a different species. Lamarck hypothesized that the adaptation of an animal to new conditions in which they live, allowing it to evolve.
Thus, he wrote in his Zoological Philosophy, about snails he had studied: "Now, if new needs become constant or very durable, animals take on new habits, which are as durable as the needs that have born. "


These theories were taken independently, some fifty years later by the British Charles Darwin and Alfred Russel Wallace. Darwin, during a scientific expedition to South America and the Galapagos Islands, had noticed that some species of the mainland and islands were very similar between them. By comparing species that sketched for the book that made him famous, "On the origin of species through natural selection." He put that in a group of animals belonging to the same species, individuals vary in their anatomical and physiological characteristics. Thus, young people are never completely identical to the parents, nor identical. This "variability native" is different from "acquired variability," in which the medium is gradually transforming the animal until such time that the species is adapted to their new living conditions.

 NB: Jean Baptiste Lamarck 1809, publishing philosophy zoologist, he proposed transmutation. He defends the idea of inheritance of acquired characteristics from one generation to another. This is the first evolutionary theory to be formulated.

NB: Charles Darwin's 1859 publication of "On the Origin of Species." Darwin proposed a scientific theory of evolution based on the principle of natural selection. It is the first to state the fact that the human race is also the result of a change due to natural selection. He did not believe in saltation. In biology, saltation is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism.

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