Now with reason dominant over instinct in man, there is a grave danger that with each man consulting his own interests instead of those of the species, some groups and even races will become exterminated. Along with reason, therefore, it is necessary that some other forces shall appear to control reason and give the interests of the species a chance to be heard along with the interests of the individual. One such force is religion. Without insisting that this is the only view which may be taken of the origin of religion, or that this is the only function of religion, we may yet assert that one of the useful purposes served by religion is to cause men to adopt lines of conduct that will be for the good of the race, although it may sacrifice the immediate good of the individual.[187] Thus if a young Mohammedan be put in the situation just described, he may decide that it is to his material interest to postpone marriage. His religion then obtrudes itself, with quotations from the Prophet to the effect that Hell is peopled with bachelors. The young man is thereupon moved to marry, even if it does cause some inconvenience to his business plans. Religion, reinforcing instinct, has triumphed over reason and gained a victory for the larger interests of the species, when they conflict with the immediate interests of the individual. From this point of view we may, paraphrasing Matthew Arnold, define religion as _motivated ethics_. Ethics is a knowledge of right conduct, religion is an agency to produce right conduct. And its working is more like that of instinct than it is like that of reason. The irreligious man, testing a proposition by reason alone, may decide that it is to the interests of all concerned that he should not utter blasphemy. The orthodox Christian never considers the pros and cons of the question; he has the Ten Commandments and the teachings of his youth in his mind, and he refrains from blasphemy in almost the instinctive way that he refrains from putting his hand on a hot stove. This chapter proposes primarily to consider how eugenics can be linked with religion, and specifically the Christian religion; but the problem is not a simple one, because Christianity is made of diverse elements. Not only has it undergone some change during the last 1900 years, but it was founded upon Judaism, which itself involved diverse elements. We shall undertake to show that eugenics fits in well with Christianity; but it must fit in with different elements in different ways. We can distinguish four phases of religion: