WEIT 2012 Chap5

THE ENGINE OF EVOLUTION

What is natural selection ?

Everywhere in nature, animals seem to fit perfectly their environement, as if they had been designed to, and early naturalists believed that this perfection was God's product. It was Charles Robert Darwin (1809-1889), who the first used the terms natural selection to describe the key process of Evolution.
In his book The Origin, he defined the natural selection as a mindless and materialistic process, gradual and nonrandom, by which some genotypical and phenotypical traits become either more or less common in a given population.

He came to this definition by realizing two things:
• The different species produce an excessive number of offspring. As the ressources are limited, they can't all survive.
• In the diverse populations, individuals vary in many heritable traits.

From these observations, he came to the fact that in a polpulation, the individuals who have the biological traits the more adapted to the environment, which fit the best their environment will be more likely to survive to predators, to feed themselves, or to find a mate, etc... As a result, and from the first observation, these individuals will be able to produce more offspring than the others, and to colonize the environment in few generations. This is what he called natural selection. Be more precise here. The definition of natural selection is very important and should be clear for you and for the other students--Pierre.brawand 28 mars 2012 à 13:43 (CEST)

Is natural selection based on chance ?

While learning Darwinism, many people understand that "everything happens by chance", but it is wrong.
A species can neither decide to evolve, nor to wait and hope to evolve. Natural selection and through it, evolution, happens because of necessity.
Adaptation to environment is inevitable.

too short--Pierre.brawand 28 mars 2012 à 13:43 (CEST)

Why is natural selection very long?

...

What are the conditions for natural selection ?

Natural selection needs three conditions:
• First of all the changing population has to be variable. For example, if the colour of the coat is changing, the population has to be diverse. ?????--Pierre.brawand 28 mars 2012 à 13:44 (CEST)
• Then, some of the variations that already exist has to come from changes in the genes. Imagine that mice with dark coat are more often eaten than the ones with light ones. If the change weren't in the genes, the process will be random and they will still be dark mice who will still be eaten more often. But if the change was in the genes, natural selection will allow more light ones to born and they will leave longer. That is why variations in the genes are needed.
• Finally, the genetic variation must allow individuals to have more offspring as others.

Not clear enough--Pierre.brawand 28 mars 2012 à 13:44 (CEST)

What is artificial selection ?

Artificial selection is a process which has the same result that natural selection but through a shortest way. It is a process that consists of a transformation of a plant or an animal into an ameliorated and more adapted form in order to satisfy human's desires in a shortest time than nature selection can.
The most obvious example is the evolution of dogs. All the species have different shapes, temperaments, colours, and sizes however they descend from a single ancestral species which is the Eurasian gray wolf. Of course they evolved because of natural selection over thousand of years but they can't be as different as they are now only through this natural selection. Some dogs for example can run faster than others or are bigger than others. This is not due to natural selection but to artificial selection. For example, because people needed faster dogs in order to win some competitions, breeders changed some traits of the dogs in order to give a size that permits it to run faster than is ancestor.
It shows that artificial selection is a shortest way to obtain what humans want and what nature can make only over thousand of years.

Good start!--Pierre.brawand 15 mars 2012 à 17:34 (CET)

What are the advantages of artificial selection?

Natural selection is very advantageous for humans.
• It is a process that can make life easier. For example, farmers can change the traits of their animals and plants in order to have best harvests and more productive animals in a shortest time. They also need to choose which traits they want to modify to win more time (and consequently more money)...

What are the disadvantages of natural selection?

Artificial selection can have dramatic results because it is not 100% safe: it can undergo mutations...

Why some people dislike artificial selection ?

...

This is not the easiest chapter of the book but it is maybe the most important to explain the mechanisms... There is a lot to do here in order to have a complete picture of the chapter. Try to organize yourself in order to share the work efficiently. OK?--Pierre.brawand 28 mars 2012 à 13:46 (CEST)

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