细菌 part 1 Hints： thermal fluctuate cell

They haven't changed because their environment has stayed the same. The water they live in bubbles up from deep in the earth, and so it's always the same temperature. But just meters away the environment is very different, away from the thermal vents with the ebb and flow of the water, the temperature fluctuates. Billions of years ago, bacteria were living here too, but as their living conditions changed, they changed as well. From one generation to the next, there were minute alterations. In themselves they were almost insignificant, but these tiny changes started the most amazing process.
Because if you add up enough tiny changes from generations through millions of generations, you can get a revolutionary transformation.
From being simple bacteria the creatures in these pools became more complicated. Single cells became groups of cells, and groups of cells early plants and animals, and the changes continued. Dozens of species became hundreds, and hundreds turned into tens of thousands. Parts of bodies were adapted to meet new challenges. Great leaps were made. A fish's fins over countless generations developed into legs and it became a reptile.

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