Which concept is part of the modern evolutionary theory, but not Darwin's original theory?

Heatamount of salt . . .

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When scientist examine data such as historical documents, they are using the "scientific methods"

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on