No one has ever said that a river doesn't obey the law of gravity. Of course they do, but there is a lot more going on than that. As far as I know, gravity is pretty universal. Would you say life evolves because of the law of gravity or it evolves under the conditions subject to the law of gravity? Maybe your statement "then I say rivers meander because they obey the Law of Gravity" would be better stated as "rivers meander while obeying the law of gravity as well as other physical laws". At least it's been a welcome diversion from the unsupportable claims against evolution.
