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ally led on to the consideration of many of the phenomena which are discussed under the head of sexual selection。 The subject is difficult and complex； and it was treated by Darwin with all the strength he could summon to the task。 It can only be dealt with here from a special point of viewthat which may serve to illustrate the influence of certain mental factors on the course of evolution。 From this point of view too much stress can scarcely be laid on the dominance of emotion during the period of courtship and pairing in the more highly organised animals。 It is a period of maximum vigour； maximum activity； and； correlated with special modes of behaviour and special organic and visceral accompaniments； a period also of maximum emotional excitement。 The combats of males； their dances and aerial evolutions； their elaborate behaviour and display； or the flood of song in birds； are emotional expressions which are at any rate coincident in time with sexual periodicity。 From the combat of the males there follows on Darwin's principles the elimination of those which are deficient in bodily vigour； deficient in special structures； offensive or protective； which contribute to success； deficient in the emotional supplement of which persistent and whole…hearted fighting is the expression； and deficient in alertness and skill which are the outcome of the psychological development of the powers of perception。 Few biologists question that we have here a mode of selection of much importance； though its influence on psychological evolution often fails to receive its due emphasis。 Mr Wallace （〃Darwinism〃； pages 282； 283； London； 1889。） regards it as 〃a form of natural selection〃； 〃to it；〃 he says； 〃we must impute the development of the exceptional strength； size； and activity of the male； together with the possession of special offensive and defensive weapons； and of all other characters which arise from the development of these or are correlated with them。〃 So far there is little disagreement among the followers of Darwin for Mr Wallace； with fine magnanimity； has always preferred to be ranked as such； notwithstanding his right； on which a smaller man would have constantly insisted； to the claim of independent originator of the doctrine of natural selection。 So far with regard to sexual selection Darwin and Mr Wallace are agreed； so far and no farther。 For Darwin； says Mr Wallace （Ibid。 page 283。）； 〃has extended the principle into a totally different field of action； which has none of that character of constancy and of inevitable result that attaches to natural selection； including male rivalry； for by far the larger portion of the phenomena； which he endeavours to explain by the direct action of sexual selection； can only be so explained on the hypothesis that the immediate agency is female choice or preference。 It is to this that he imputes the origin of all secondary sexual characters other than weapons of offence and defence。。。In this extension of sexual selection to include the action of female choice or preference； and in the attempt to give to that choice such wide…reaching effects； I am unable to follow him more than a very little way。〃
Into the details of Mr Wallace's criticisms it is impossible to enter here。 We cannot discuss either the mode of origin of the variations in structure which have rendered secondary sexual characters possible or the modes of selection other than sexual which have rendered them； within narrow limits； specifically constant。 Mendelism and mutation theories may have something to say on the subject when these theories have been more fully correlated with the basal principles of selection。 It is noteworthy that Mr Wallace says （〃Darwinism〃； pages 283； 284。）： 〃Besides the acquisition of weapons by the male for the purpose of fighting with other males； there are some other sexual characters which may have been produced by natural selection。 Such are the various sounds and odours which are peculiar to the male； and which serve as a call to the female or as an indication of his presence。 These are evidently a valuable addition to the means of recognition of the two sexes； and are a further indication that the pairing season has arrived； and the production； intensification； and differentiation of these sounds and odours are clearly within the power of natural selection。 The same remark will apply to the peculiar calls of birds； and even to the singing of the males。〃 Why the same remark should not apply to their colours and adornments is not obvious。 What is obvious is that 〃means of recognition〃 and 〃indication that the pairing season has arrived〃 are dependent on the perceptive powers of the female who recognises and for whom the indication has meaning。 The hypothesis of female preference； stripped of the aesthetic surplusage which is psychologically both unnecessary and unproven； is really only different in degree from that which Mr Wallace admits in principle when he says that it is probable that the female is pleased or excited by the display。
Let us for our present purpose leave on one side and regard as sub judice the question whether the specific details of secondary sexual characters are the outcome of female choice。 For us the question is whether certain psychological accompaniments of the pairing situation have influenced the course of evolution and whether these psychological accompaniments are themselves the outcome of evolution。 As a matter of observation； specially differentiated modes of behaviour； often very elaborate； frequently requiring highly developed skill； and apparently highly charged with emotional tone； are the precursors of pairing。 They are generally confined to the males； whose fierce combats during the period of sexual activity are part of the emotional manifestation。 It is inconceivable that they have no biological meaning； and it is difficult to conceive that they have any other biological end than to evoke in the generally more passive female the pairing impulse。 They are based on instinctive foundations ingrained in the nervous constitution through natural （or may we not say sexual？） selection in virtue of their profound utility。 They are called into play by a specialised presentation such as the sight or the scent of the female at； or a little in advance of； a critical period of the physiological rhythm。 There is no necessity that the male should have any knowledge of the end to which his strenuous activity leads up。 In presence of the female there is an elaborate application of all the energies of behaviour； just because ages of racial preparation have made him biologically and emotionally what he isa functionally sexual male that must dance or sing or go through hereditary movements of display； when the appropriate stimulation comes。 Of course after the first successful courtship his future behaviour will be in some degree modified by his previous experience。 No doubt during his first courtship he is gaining the primary data of a peculiarly rich experience； instinctive and emotional。 But the biological foundations of the behaviour of courtship are laid in the hereditary coordinations。 It would seem that in some cases； not indeed in all； but perhaps especially in those cases in which secondary sexual behaviour is most highly evolved；correlative with the ardour of the male is a certain amount of reluctance in the female。 The pairing act on her part only takes place after prolonged stimulation； for affording which the behaviour of male courtship is the requisite presentation。 The most vigorous； defiant and mettlesome male is preferred just because he alone affords a contributory stimulation adequate to evoke the pairing impulse with its attendant emotional tone。
It is true that this places female preference or choice on a much lower psychological plane than Darwin in some passages seems to contemplate where； for example； he says that the female appreciates the display of the male and places to her credit a taste for the beautiful。 But Darwin himself distinctly states （〃Descent of Man〃 （2nd edition）； Vol。 II。 pages 136； 137； （Popular edition）； pages 642； 643。） that 〃it is not probable that she consciously deliberates； but she is most excited or attracted by the most beautiful； or melodious； or gallant males。〃 The view here put forward； which has been developed by Prof。 Groos （〃The Play of Animals〃； page 244； London； 1898。）； therefore seems to have Darwin's own sanction。 The phenomena are not only biological； there are psychological elements as well。 One can hardly suppose that the female is unconscious of the male's presence； the final yielding must surely be accompanied by heightened emotional tone。 Whether we call it choice or not is merely a matter of definition of terms。 The behaviour is in part determined by supplementary psychological values。 Prof。 Groos regards the coyness of females as 〃a most efficient means of preventing the too early and too frequent yielding to the sexual impulse。〃 （Ibid。 page 283。） Be that as it may； it is； in any case； if we grant the facts； a means through which male sexual behaviour with all its biological and psychological implications； is raised to a level otherwise perhaps unattainable by natural means； wh