200 THE POPULAR SCIENCE MONTHLY 



THE ROLE OF SEX IN THE EVOLUTION OF MIND 



By Professor S. J. HOLMES 



THE UNIVERSITY OF CALIFORNIA 



THE reason for the existence of sex is one of those biological problems 

 which has long perplexed the scientific world, and to-day its solu- 

 tion seems as remote as it did a century ago. Many remarkable dis- 

 coveries have been made in regard to the microscopic structure and 

 development of the germ cells. We have learned much of the general 

 biology of sex, and the probable evolution of sex in the organic world. 

 And substantial progress has been made in respect to the old problem 

 of the determination of sex. But to the question, Why came there to be 

 two sexes at all? or, in other words, Why did not organisms continue 

 to reproduce asexually as it is probable they once did ? we can only offer 

 answers that, at best, are very hypothetical. The bacteria and the blue- 

 green algse, so far as careful investigation has yet ascertained, reproduce 

 exclusively by the asexual method, usually by fission or the formation 

 of spores. But among the higher plants and in nearly all animals we 

 find the existence of two sexes of very general occurrence. While the 

 fact that sex is absent in the lowest forms of life indicates that evolu- 

 has proceeded, at least a certain distance, without its aid, and suggests 

 the possibility of the evolution of sexless forms of a high degree of 

 organization, yet the general prevalence of sex in all but the most primi- 

 tive organisms points to the conclusion that sex has played a funda- 

 mental role in the evolution of the organic world. There are many 

 theories as to the part which sex has played, but the profound disagree- 

 ment among several of these which have secured the widest following is 

 significant of how little is positively established in regard to this subject. 

 While the cause of the development of sex may remain obscure, it is 

 not difficult to point out some of its consequences, although it would be 

 futile to attempt a very accurate picture of what the organic world would 

 be had sex never been evolved. Even if the processes of variation and 

 selection had gone on to the same extent — which is scarcely probable — 

 the absence of sex would have given a very different direction to evolu- 

 tion from that which was actually followed. Many of the most complex 

 structural arrangements of organisms have especial reference to the 

 union of the germ cells. The color and scent of flowers, and their many 

 and beautiful adaptations to secure cross fertilization would never have 

 appeared if plants were propagated exclusively by the asexual method, 

 and this would doubtless have entailed more or less extensive changes 

 in other parts of the organism. In animals the structural peculiarities 



