Tool Module: What Is Evolution?

People have always been trying to explain the origin and profusion of the forms of life on Earth. Over the centuries, many explanations have been offered. One was fixism: the doctrine that the species living on Earth have always been the same and have not evolved since their creation. Another was Lamarck's theory of the transmission of acquired characteristics, based on the idea that populations are gradually transformed as the direct result of the environmental constraints they face.

But the theory that has ultimately been confirmed by the facts is Darwin's, that species evolve through mutations, followed by natural selection.

Histoire: La théorie de l'évolution (I)Histoire: Histoire des idées sur l'évolutionHistoire: Vers la grande synthèse : la théorie de l’évolutionHistoire: A history of evolutionary tought

For nearly two centuries now, so many confirming observations have been accumulating that we can now state that evolution is a phenomenon that has in fact occurred and continues to occur today. All the evidence, from disciplines as diverse as paleontology, genetics, anatomy, chemistry, and geography, converges to confirm the existence of evolution.

Lien: Evidence of EvolutionLien: Introduction to Evolutionary BiologyLien: LES PREUVES DE L'ÉVOLUTIONLien: Quelles sont les preuves de l'Évolution ?Lien: Extrait du livre « Le miroir du monde »de Cyrille Barrette

Scientists have now discovered that natural selection was not the only mechanism of this evolution. But they can state that all living species are the product of evolution and are derived from common distant ancestors.

Ironically, it is often the great diversity and complexity of the forms of life that makes the idea of evolution so difficult for so many people to accept. They find it hard to imagine that random genetic mutations, combined with a natural selection mechanism, could be solely responsible for such complex beings as humans, and such complex organs as their brains. They find it more logical to believe that the human brain was “designed” by some divine engineer — hence the persistent attraction of creationism.

But the human brain was not designed by any engineer. It is a product of evolution, a series of small changes that have accumulated gradually over very long periods. And that is the real reason that people have so much trouble with the idea of evolution: the geologic time scale on which it takes place.

Lien: The Cosmic CalendarLien: The Universe in one yearLiens: Cosmic Calendar (From The Dragons of Eden - Carl Sagan)

On the time scale of a human life, to design a complex machine, someone must first decide on its function, then draw up plans for a mechanism that can perform that function, and then manufacture that mechanism. But that is not how the process of evolution produced the human brain. Evolution built on top of what it already had to work with, rather than starting from zero. On the scale of a human life, this approach is totally inefficient; it would be like trying to build a car by modifying a wheelbarrow. But on the geologic time scales on which life evolves, it works just fine.

Here it is important to stress that evolution does not have a plan. Human beings are an accident of evolution, just like carnivorous plants or the duck-billed platypus. The larger brains that appeared late in the course of evolution are not “better” than the smaller ones that came before them. Evolution is an ongoing exploration of the variability created by chance mutations in existing forms of life. When a trait appears later in evolution, it just means that evolution is trying something new, not that it has necessarily found a better alternative.

Lien: Interview  with Stephen Jay Gould, author of Full House: The Spread of Excellence from Plato to Darwin. Lien: THE EVOLUTION OF LIFE ON THE EARTHLien: Is There Progress and Direction in Evolution?

In fact, when you consider how the activities of some groups of humans are threatening the planet Earth today, you may well wonder whether the advent of our species was really such a great idea on evolution's part.

Lien: Evolution  Lien: EVOLUTION LESSONSLien: Frequently Asked Questions About EvolutionLien: Questions and answers on evolutionLien: Evolution WingLien: If cognitive ability confers an evolutionary advantage, why are humans (apparently) so unique in this trait?Lien: The Tree of Life
Lien: Cours sur l’ÉvolutionLien: Biology Links: EvolutionLien: Brain Evolution:Expanding Our MindsLien: L'évolution des espècesLien: Evolving Ideas: Isn't Evolution Just a Theory? (Video, lenght 6:15)Lien: What is science ? nombreux liens...Lien: Evolution is a Fact and a Theory
Lien: Evolution as Fact and TheoryLien: What is the evidence for evolution ?Lien: l'évolutionLien: L'Évolution : Diaporama PP : l’évolution 1Outil: La sélection naturelle de Darwin Lien: Vers une loi généralisée de l’évolutionLien: WHAT IS A SPECIES?
Lien: EvolutionLien: Biology and Evolutionary TheoryLien: Les modèles informatiques de l'évolutionLien: Life dropLink : Evolution


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