Why didn’t Darwin think you could observe natural selection in a lifetime?

There aren't enough generations visible within a lifetime to have any visible changes or evidence of natural selection. Essentially, evolution takes much longer than 1 lifespan to happen.

relative humidity, temperature and dew point -- are bound together in the mathematical relationship below. relative humidity changes when temperatures change. because warm air can hold more water vapor than cool air, relative humidity falls when the temperature rises if no moisture is added to the air. so i would say a

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