In the second place, again, it must not be forgotten that falling in love has never yet, among civilised men at least, had a fair field and no favour.  Many marriages are arranged on very different grounds—­grounds of convenience, grounds of cupidity, grounds of religion, grounds of snobbishness.  In many cases it is clearly demonstrable that such marriages are productive in the highest degree of evil consequences.  Take the case of heiresses.  An heiress is almost by necessity the one last feeble and flickering relic of a moribund stock—­often of a stock reduced by the sordid pursuit of ill-gotten wealth almost to the very verge of actual insanity.  But let her be ever so ugly, ever so unhealthy, ever so hysterical, ever so mad, somebody or other will be ready and eager to marry her on any terms.  Considerations of this sort have helped to stock the world with many feeble and unhealthy persons.  Among the middle and upper classes it may be safely said only a very small percentage of marriages is ever due to love alone; in other words, to instinctive feeling.  The remainder have been influenced by various side advantages, and nature has taken her vengeance accordingly on the unhappy offspring.  Parents and moralists are ever ready to drown her voice, and to counsel marriage within one’s own class, among nice people, with a really religious girl, and so forth ad infinitum.  By many well-meaning young people these deadly interferences with natural impulse are accepted as part of a higher and nobler law of conduct.  The wretched belief that one should subordinate the promptings of one’s own soul to the dictates of a miscalculating and misdirecting prudence has been instilled into the minds of girls especially, until at last many of them have almost come to look upon their natural instincts as wrong, and the immoral, race-destructive counsels of their seniors or advisers as the truest and purest earthly wisdom.  Among certain small religious sects, again, such as the Quakers, the duty of ‘marrying in’ has been strenuously inculcated, and only the stronger-minded and more individualistic members have had courage and initiative enough to disregard precedent, and to follow the internal divine monitor, as against the externally-imposed law of their particular community.  Even among wider bodies it is commonly held that Catholics must not marry Protestants; and the admirable results obtained by the mixture of Jewish with European blood have almost all been reached by male Jews having the temerity to marry ‘Christian’ women in the face of opposition and persecution from their co-nationalists.  It is very rarely indeed that a Jewess will accept a European for a husband.  In so many ways, and on so many grounds, does convention interfere with the plain and evident dictates of nature.