genetic drift
"Imagine a game in which you have a bag holding 100 marbles, 50 of which are brown and 50 green. You are allowed to draw 10 marbles out of the bag. Now imagine that the bag is restocked with 100 marbles, with the same proportion of brown and green marbles as you have just drawn out. The game might play out like this:"
see the link.
"There are various and overlapping theories regarding evolution. Here the term "theories" is meant as it is applied in common usage, not the strict scientific definition. Genetic drift is like a relaxed form of natural selection. Adaptive mutation, as I understand it, is like natural selection on steroids. To what degree either or both have had an influence on overall evolution has yet to be determined. There is room for discusion."
"Genetic drift is like a room with flypaper on all the walls. The walls represent loss and fixation, and sooner or later (depending upon population size, which in this analogy is directly related to the size of the room)," the fly(the allele frequency), will hit a wall and be stuck.
"The way I think about genes and genetic drift is as a clay sculpture of a beautiful woman's face. It's finely and delicately contoured. She has a pointed noise, raised cheek bones, large almond eyes, and a well defined chin that just sticks right out there. Then you get out a sandblaster and start blasting off the features around the main shape of the head. In the end, you've still got a head, but no ears, no nose, or mouth. Genetic drift is like the sandblaster that rips defined features off the organism. The resulting genetic variation can be thought of as the newly created real estate on the face. Now new things can be made!"
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