The scientific view is that the common laws are due to common human experience, which is much the same everywhere. It is closely allied with the doctrine of evolution as applied to human institutions. If we could only assume that the nations developed each separately and independently, without mutual intercourse, it might suffice. But for ages before the institutions we are considering, both Babylonia and Palestine had been the meeting-place of many peoples. We cannot tell by any _a priori_ method which race introduced which custom. All we know is that an improvement is often readily adopted by people from those with whom they come in contact, even when not forced upon them by conquest. But we also know that even superior usefulness or comfort is not always sufficient to keep a custom alive. We now know that without much apparent reason even an essential craft may die out. In fact, this common humanity origin of common customs is very useful, like the theory of evolution, to account for observed results when we have no knowledge of what preceded them and can only guess at the previous history. One can then, without fear of contradiction, assert what we consider most likely to have led up to them as their antecedents. But these easy explanations do not absolve us from careful research where history can be produced to work upon. The evolution of human institutions, if such be a legitimate expression to use, has many a set-back or reaction, and we may very well at any time be comparing progress in one history with reaction in another.