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• 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.<br> | • 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.<br> | ||
• Finally, the genetic variation must allow individuals to have more offspring as others. | • Finally, the genetic variation must allow individuals to have more offspring as others. | ||
=What is artificial selection ?= | |||
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*retour à [[Evolution_3BIbDF10-11_2011/12]]<br> | *retour à [[Evolution_3BIbDF10-11_2011/12]]<br> | ||
*retour à [[Accueil]] | *retour à [[Accueil]] | ||
Version du 14 mars 2012 à 22:01
THE ENGINE OF EVOLUTION
What is natural selection ?
Darwin realises two things:
• The different species produce an excessive number of offspring. As the resources are limited, they can't all survive.
• In the diverse populations, individuals vary in many heritable traits.
From these observations, he comes to the fact that the individuals that have the best traits to live will be more likely to survive.and they will be able to have more offspring than the others. This is what he called natural selection.
Is natural selection based on chance ?
While learning Darwinism, many people understand that "everything happens by chance", but it is wrong.
If natural selection was only based on chance, many species would have go extinct.
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.
• 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.
What is artificial selection ?
- retour à Evolution_3BIbDF10-11_2011/12
- retour à Accueil