The conspiracy theory has been widely discredited and debunked. However, racial theories have been discredited. Scientific investigations have repeatedly discredited such claims. Selective refutation involves searching for plausible theories that enable criticism to be discredited. Most of these hypotheses have been discredited or rejected. This myth has been discredited by scholars for lack of evidence. Phrenology was mostly discredited as a scientific theory by the 1840s. This theory has been discredited by later findings. This view has been largely discredited by modern research. However allegations about the Zero being a copy have been discredited by some authors. His claims are now generally discredited by ghost historians. Behavioural genetics was thereby discredited through its association to eugenics. These ideas have since been discredited by some historians. Although widely believed at the time, these claims were later discredited. More important, says Potter, they permanently discredited Manifest Destiny and "popular sovereignty" as political doctrines.