Some evolutionary biologists have argued that the neutral theory should be taken as the null hypothesis to explain genetic variation within species or populations and genetic differences among them. In this view, adaptation and natural selection should be the preferred explanation only if genetic drift cannot explain the data. Others might argue that since there is so much evidence that natural selection has shaped species' characteristics, selection should be the explanation of choice and that the burden of proof should fall on advocates of the neutral theory. Why might one of these points of view be more convincing than the other?