Gravity in the same essence - is not 100% understood - but we are able to manipulate it ,and yes we do know basically , how it works - or at least about 90% and are able to engineer around it.
You're confusing cause and effect. We can readily see and measure the effects of gravity, that is how engineers design planes and everything else. We can NOT manipulate it, no one can turn it on or off or adjust its force.
We can't see gravity, only measure its effect on our world. Evolution is similar in that we can't easily see it directly but we can see the effects it has on the fossil record and the biology of living organisms.