Evolution and gravity Two peas in a scientific pod

The fact of gravity is beyond dispute. When you drop something, it falls — a fact that most (dare I say all?) of us have personally established, either intentionally or accidentally. We not only know that things fall, but we also know a few details about the falling process. We know that whatever we drop falls toward the Earth, and we can measure the downward acceleration. We know that the pull of gravity is different away from Earth. On a smaller body such as the moon, things don't fall as fast. In deep space, far from the Earth and the moon, things don't fall at all; they just float. The strength of this attractive force (a fancy way of saying gravity) has to do with the mass of the attractive body and the other object's distance from it. The moon, for example, which is smaller than Earth, has less gravity.

Humans know all these things about gravity, but it turns out that we're not exactly sure what gravity is or how it works. Why, for example, does a dropped object go down rather than up? Scientists in the field of physics called gravitational theory are trying to figure these things out, and they continually fine-tune their theories as more information becomes available. But just because they can't say definitively what gravity is doesn't mean that gravity is any less real.

Just because you and I don't understand gravitational theory doesn't affect how we interact with gravity on a daily basis. We know it happens even if we don't know why, and we take it into consideration when we launch things into space, skateboard, land an airplane, or try to get that nine-iron shot onto the green. The same is true of evolution: We have the facts of evolution (the aspects of heritable changes in living organisms that we can see and measure), and we have the processes that evolutionary biologists theorize are responsible for these facts. As it turns out, compared with their theories about gravity, scientists have an excellent understanding of the basic process of evolution.

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