WEIT Chap5
The Engine of Evolution
The engine of evolution
We have many proofs that adaptatioin occur in amnimals, for example the woodpecker has a really strong skull and muscles that allow him to do his drumming. In his book "The Origin" of Charles Darwin he explained that that was "natural selection" that triggered it.
However there are problems, there are not unattackable proofs for evolution. First, evolution was extremely slow and so it is impossible to observe the new evolutions in a lifetime.
Natural selection is a process not a mechanism, it happens and it is independant from any external will.
There are three things involved in creating an adaptation by natural selection:
1)The starting population has to b e variable (genetically speaking)
2)The variations must be able to be transmitted by the genes. (heritability)
3) The genetic variation must affect an individual's probability of leaving offspring
In evolution everything happens "by chance" "by accident" The filtering of that variation by natural selection produce adaptations and this is not random. The problem is that it must explain complex physiological traits.
Ozgul and Marie Charlotte: on pense qu'il faudrait refaire toute la première partie p.111-122 pour expliquer les problèmes soulevés par Coyne sur la natural selection de Darwin. Pcq ici c'est très bordelique ce qu'on a marqué donc voilà good luck! =)
Evolution without selection
Genetic drift: Helps natural selection to build evolution. It is a random fact that in a probalistic situation that an outcome comes more often than the other: For example in a F1 generation one parent having a AB (one A and one B allele) blood type, if the parent has only 1 child it will transmit only one of the two alleles and the other one would be lost. (the parent could have 4 children and the same problem, always randomly give one of the two alleles.)(cf. p.122)
difference between Nat selec and gen drift
Natural selection will select only the useful features whereas the genetic drift is random and can generate useful or harmful changes. Genetic drift happens because there are only limited amount of offsprings (the ideal probability will thus not be respected since there are not an infinity of them. It is impossible to reach an ideal probability as we seen in maths when there are not an infinite of "tries")
Animal and plant breeding
artificial selection: the human can choose for a given species which individuals are to reproduce and thereby enhance a particular feature from the two previous genetic material (cf. ETIVAZ documentary on cows seen in class) Thanks to this process men has "created" new domestic dog races from the original wolf. This selection has been done really quickly so we can think that natural selection takes more time and tries and can build much more diversity.
difference between nat selec and artif selec
In artificial selection this is the breeder rather than the nature who sort out which variants are good or bad. In other words, the criterion of reproductive success is human desire rather than adaptation to a natural environment.
Proof that natural selection occurs and evolution is true because we can observe it. IT is now easier to accept natural evolution since we have seen that artificial selection happens."
evolution is the test tube
Try to show what happens in nature by observing it in laboratory. We change for exeemple the environment of a given organisme let's say bacterias. We change their environment in order to see how they can adapt themselves and how selection occurs. Bacterias are good because a new generation is done every 20min and it is easier in a lifetime to observe changes.
resistance to drugs and poisons
Viruses. The big problem is that the virus adapt themselves to the new environment of antibiotics according to natural selection. The weak ones are killed and only the resistant ones develop.(this is why each year the flu vaccin changes.)
Fortunately not all pathogens don't adapt to treatments for example measles didn't manage to evolve and to develop a resistance to the new vaccine.
Selection in the wild
Selection in nature is really slow to happen. That's why it is hard to believe for some people because they want to observe it in a lifetime. We may however observe microevolutions as well as macroevolution in species that reproduce quickly (such as bacteria and viruses).
Can selection build complexity?
If you let time the natural selection can build big things because we have seen that artificial selection has changed things.
We will never be able to reconstruct how selection created everything, some things will always be unknown due to lack of data and to the huge amount of information that we should know.
"What is the alternative theory? Creationism." Some people are not convinced by this theory because we don't know everything.
expliquez mieux ce que c'est la complexity
Vocabulary List
artificial selection =
random = regardless of wether it is useful to the individual
heritability = the genetic basis of a variation
process = a description of how genes that produce better adaptation become more frequent over time, without external will.
mechanism = a process imposed on a population from the outside
fitness = average number of offspring
mutation =
neutral variation = a variation which is neither good or bad
environment =
macroevolution = transforming one "type" of plant by evolution.
microevolution = small changes in one or a few features of a species.
stabilizing selection = when an animal is perfectly adapted the only evolution which is happenning is the stabilizing selection, it will approach itself to the golden mean.
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