In a recent series of posts (Embryo screening should be mandatory, Allowing children to be born with severe disease is morally equivalent to child abuse, round 2, and Arguments against routine screening for severe disease genes; food for thought), Daniel MacArthur over at Genetic Future has discussed the issue of genetic screening of potential parents and embryos so that genetic diseases can be avoided in the population. Many of the arguments revolve around moral issues, with some discussion on the accuracy of such testing. In this argument, as for many of its ilk, the lines are drawn and scientists end up on one side and ethicists end up on the other. In this case, scientists are typically in favor of genetic screening and ethicists typically oppose it. That is why these arguments, from scientists, center on the "ethical" reasons supporting genetic screening. Unfortunately, the singular focus on ethical arguments forces all other concerns, e.g., scientific concerns, to the background. So, are there scientific reasons not to screen embryos for known disabling genetic markers? Well, quite possibly, but human hubris is not likely to give one of them much weight: what makes us think we can do a better job than nature in selecting traits that are suitable for survival? How can we be certain that some of these markers determined to be detrimental are not in linkage disequilibrium with traits that increase survivability for the overall population? In other words, will the elimination of these traits also eliminate other, favorable traits? Would the widespread practice of eugenics decrease the natural variation in our species such that our ability to survive environmental change is reduced? Contrarily, given the current state of science and our existing political structures, are Homo sapiens still even susceptible to natural selection? Finally, if we are unable to replicate even relatively simple biological processes, e.g., fixation of nitrogen at room temperature and the efficient conversion of sunlight to energy, how can we hope to properly navigate the human biological system? It seems to me that these are the sorts of questions that need to be answered before the ethical questions, which are important, should even be asked.