What Is Evolution
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It is much easier to see if you look into the past. Most organisms have two eyes, two ears, five toes and five fingers. Slowly, over millions and millions of years, all the organisms have evolved, starting from bacteria, molluscs, then fish, and slowly to more developed animals. And on every level, as well as within species, evolution has created plenty of diversity.
It happens by a random mutation happening every so often within inherited characteristics. If the mutation does not suit the environment, obviously the individual is disadvantaged compared to other individuals, the individual is less likely to reproduce so the characteristic is less likely to survive. If the mutation suits the environment better than the original inherited characteristics would have been, it has good chances to be passed on to future generations and start a 'new trend'.
That is what Charles Darwin means by the 'survival of the fittest' in his theory of evolution.
There are some things that get mistaken with what is evolution:
* Evolution only works over a long enough time. That time is different for each species. Insects for example have really short life time and a quick generation turnover. They adapt to new conditions quickly (which is a big evolutionary advanatge), so evolution works on them in quite a short time. Humans, on the other hand, have a slow generation turnover, so a couple of hundreds or even a thousand of years is not a long enough time for evolution to affect us. We need more like a ten thousand of years at the very least.
* Evolution strives to perfection but is not always perfect. Evolution hasn't stopped, (and will never, because the mutations will always happen and the conditions in our environment will always change, so there will always be room for improvement), so you cannot look at a characteristic and say, what is this good for - it has to be good for something? Not necessarily. We have rudimentary organs, we have characteristics that are not exactly good for something. If a characteristic is neither exactly good or exactly bad it can be carried on through generations. It has to be bad, it has to be of a direct disadvantage, for the evolution to 'get rid of it'.
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