Why is evolution not taught in every school?
It shouldn’t be controversial, but it is to some folks who don’t understand science, don’t understand religion, or both. Evolution is all about the natural changes that accumulate in populations over time. The mechanism by which this happens is pretty well understood and is described in the modern synthesis of the theory of evolution. It’s got everything a scientific theory needs: it explains an observed phenomenon or set of data, it is internally consistent and consistent with other branches of science, it is supported by vast fields of evidence from many different scientific disciplines (each of which are in turn supported by their own mountains of evidence), and it has been extensively tested. Each time it has been tested, it has passed with flying colors. The last aspect that makes the modern synthesis a true scientific theory is that it is falsifiable. Even one damning piece of evidence would require at least a modification of the theory, and at most a complete restructuring of it
