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How fast can evolution take place?
We usually think of evolution of some process that takes thousands or millions of years.
WRONG !

OK, the really big changes need some time to show up. To evolve from a dinosaurus to a bird cannot happen overnight.

But it does not take centuries to see evolution. This studies on guppies show that evolution can go a lot faster.

It all depends on your definition of evolution. For example R.P.Worden uses in a somewhat theoritical article the “rate of increase of Genetic Information in the Phenotype” to measure evolution speed.
I find this a bit silly. If the genetic information does not increase, but nevertheless changes is that not evolution too ? As if you say that two different books of 350 pages each are the same book because of the same number of pages !

I think evolution works on a much smaller scale : whenever the genetic content of a population has changed between two generations there has been evolution !
This simply means that evolution takes place constantly, because there are always tiny changes between following generations.

In the guppy article, the experiment consisted in putting guppies in two different environments. Everyone familiar with evolution knows that evolution is caused by changes in the environment.

Important changes cause fast evolution, like the guppy experiment, where they saw significant evolution in 10 years.

But it can go even more rapidly : during a cold winter on the average the smallest birds in a population suffer most because their lose more heat than the bigger ones (the Bergmann rule). This means that after an extremely cold winter the average size of a bird population has increased, because the big ones survived better. Since size is inherited it is obvious that the genetic content of the population has changed. IN ONLY ONE WINTER !

Did you enjoy this post ? Then you might be interested in the following :
Human evolution : the future of men
top-10 lists on evolution
Evolution of minerals
Evolution in blue and red
The end of evolution

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