How does evolution account for symmetry?

Natural selection doesnt make any sense as an explanation for how things came to be. I guess strong species of animals kill weak ones. But, the killing is usually cyclical, where animals are killed off but reproduce to keep their populations in balance. Generally, extinction seems to occur like when something like an asteroid hits the planet or people kill them off constantly enough. So I guess, people can killl them off and in that instance, natural selection is true. But even fossils are symmetrical. So the whole idea that beneficial mutations beat out negative mutations to get the symmetry we see doesnt seem likely to me, because if it was, there'd at least be some sort of fossil that DID have random positions of feet and hands and arms and all that. Theistic evolution i suppose is plausible. But even the whole tree of life thing that says that every living thing, could it be upside down?. Whatever killed the dinosaurs, killed most of life on the planet, So would it not stand to reason that a lot of the fossils of extinct animals are NOT of weaker animals waiting to evolve into something better, but of animals that, like the dinosaurs, became extinct around the same period, because of the same asteroid impact? Not only that but a m extinction should cut evolution off from occurring over billions of years to having to occur over only hundreds of millions of years. Yet. Supposably evolution can only occur if you give it over tons and tons of generations so any changes are supposed to be too small to even observe. Sure, microscopic organisms can change and be observed and "mutate", but does that mean they can become a bear or a functioning person even if you give them a billion years? Animals can reproduce within their kind. Different breeds of dogs can obviously mate. But that doesnt mean a person and a monkey, who are apparently evolutionary cousins, can mate and have a Humonkey or something does it? Its kinda gross to think about, but over the years im sure people have tried different disgusting things or experimented and no ones come up with any breed of human-monkeys. So how then does evolution account for symmetry if even ancient fossils are symmetrical? I just do not see how it makes any logical sense.