Darwin - Evolution
Texte du Storyboard
- Let's explain together what are the four mechanisms of the evolution of species!
- - Chapter 1 : Mutations- Chapter 2 : Natural selection- Chapter 3 : Genetic drift - Chapter 4 : Reproductive isolation
- EVOLUTION
- A G T C C
- T C C A G G
- First of all, MUTATIONS ... You see the road, it's actually a strand of DNA, which is used to build our body and make it work.We can see on it, the little guys called nucleotides. There are the red ones with the letter T associated with the A-blue ones. The C-yellow ones with the G-pink ones.But when they multiply, sometimes there are random errors... Some of them can DISAPPEAR or CHANGE their color and letter, which causes DISEASES or CHANGES in the body.
- Mutations
- Now let's see the NATURAL SELECTION! There are TWO butterfly species and a frog, a PREDATOR. It eats butterflies. At night the frog doesn’t see the brown butterflies but it can see the yellow ones, so it eats it. Gradually there are less yellow butterflies because they don't survive, they are EATEN more easily. The descendants of the brown butterflies are brown too, little by little yellow butterflies DISAPPEAR, it’s the natural selection !
- Natural Selection
- Then the GENETIC DRIFT! It is a random modification of alleles in a population over successive generations. (Alleles are VERSIONS OF THE GENE, for example for the "eye colour" gene, the alleles are "blue" and "brown") Some individuals do not have children so their alleles are not transmitted. In this group, the "brown" allele disappears. Genetic drift occurs more rapidly when there are few individuals in the population.
- Genetic Drift
- Finally, REPRODUCTIVE ISOLATION is when the same species ADAPTS to two environments. It CHANGES and becomes two DIFFERENT SPECIES that can no longer have descendants who are not sterile. A long time ago horses and zebras were part of the same species, but they reproduced on their own (like horses in Europe and zebras in Africa). Now they are TOO DIFFERENT to have an unsterile baby together.
- Reproductive isolation
- Now you know that each species has not always been the way they are today. Each one had changed thanks to these four MECHANISMS from Darwin's theories.
- EVOLUTION OF SPECIES
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