There is a certain attitude about the application of science to human life with which I have some sympathy, though I do not, in the last analysis, agree with it. It is the attitude of those who dread what is “unnatural.” Rousseau is, of course, the great protagonist of this view in Europe. In Asia, Lao-Tze has set it forth even more persuasively, and 2400 years sooner. I think there is a mixture of truth and falsehood in the admiration of “nature,” which it is important to disentangle. To begin with, what is “natural”? Roughly speaking, anything to which the speaker was accustomed in childhood. Lao-Tze objects to roads and carriages and boats, all of which were probably unknown in the village where he was born. Rousseau has got used to these things, and does not regard them as against nature. But he would no doubt have thundered against railways if he had lived to see them. Clothes and cooking are too ancient to be denounced by most of the apostles of nature, though they all object to new fashions in either. Birth-control is thought wicked by people who tolerate celibacy, because the former is a new violation of nature and the latter an ancient one. In all these ways those who preach “nature” are inconsistent, and one is tempted to regard them as mere conservatives. Nevertheless, there is something to be said in their favour. Take for instance vitamines, the discovery of which has produced a revulsion in favour of “natural” foods. It seems, however, that vitamines can be supplied by cod-liver oil and electric light, which are certainly not part of the “natural” diet of a human being. This case illustrates that, in the absence of knowledge, unexpected harm may be done by a new departure from nature; but when the harm has come to be understood it can usually be remedied by some new artificiality. As regards our physical environment and our physical means of gratifying our desires, I do not think the doctrine of “nature” justifies anything beyond a certain experimental caution in the adoption of new expedients. Clothes, for instance, are contrary to nature, and need to be supplemented by another unnatural practice, namely washing, if they are not to bring disease. But the two practices together make a man healthier than the savage who eschews both.