I'm experiencing the fast paced evolution in my tank. I started with one pregnant, female, feeder guppy. Then I had about 2 dozen little guppies swimming around for a while. Till some of them got eaten or died off. Now there are only a few of that generation that are almost full size. Then there were some fry, that were born larger and with color. Those are getting bigger. And my most current generation consists of large fry, for guppies, with lots red, blue, and black.
I don't really believe in evolution being how Earth is how it is now. But this is showing that it does/can happen.
55g - 1 oscar and 1 red zebra
30g(planted) - 3 Trilineatus cories, 3 peppered cories, 1 female betta, 2 gold rasboras, and snails.
50g - 4 lethrinops intermedius
46g Hex - 2 black neon tetras, 3 bloodfin tetras, 3 blue tetras, 2 snakeskin gouramis, 3 Agassizi corys, 2 von rio tetras ,and 1 pleco