An ideal view is sketched of the relationship between the facts established in science and the values of ethics and politics, and of the distinction between them. Some necessary qualifications are drawn, which do not essentially undermine the ideal. Then two cases of scientific work are considered in which considerations of value may in different ways be playing a more intimate role in the science than the ideal would suggest. These are Darwin's theory of evolution and the current consensus on climate change. Are any general lessons to be drawn from these cases?