308 THE ZOOLOGIST. 



may be taken to indicate that segregation can happen at earlier stages 

 of differentiation. 



The paradoxical descent of colour-blindness and other sex-limited 

 conditions — formerly regarded as an inscrutable caprice of nature — 

 has been represented with approximate correctness, and we already 

 know something as to the way, or, perhaps, I should say ways, in 

 which the determination of sex is accomplished in some of the forms 

 of life — though, I hasten to add, we have no inkling as to any method 

 by which that determination may be influenced or directed. It is 

 obvious that such discoveries have bearings on most of the problems, 

 whether theoretical or practical, in which animals and plants are 

 concerned. Permanence or change of type, perfection of type, purity 

 or mixture of race, " racial development," the succession of forms, 

 from being vague phrases expressing matters of degree, are now seen 

 to be capable of acquiring physiological meanings, already to some 

 extent assigned with precision. For the naturalist — and it is to him 

 that I am especially addressing myself to-day — these things are 

 chiefly significant as relating to the history of organic beings — the 

 theory of Evolution, to use our modern name. They have, as I shall 

 endeavour to show in my second address to be given in Sydney, an 

 immediate reference to the conduct of human society. 



I suppose that everyone is familiar in outline with the theory of 

 the Origin of Species which Darwin promulgated. Through the last 

 fifty years this theme of the Natural Selection of favoured races has 

 been developed and expounded in writings innumerable. Favoured 

 races certainly can replace others. The argument is sound, but we 

 are doubtful of its value. For us that debate stands adjourned. We 

 go to Darwin for his incomparable collection of facts. We would 

 fain emulate his scholarship, his width and his power of exposition, 

 but to us he speaks no more with philosophical authority. We read 

 his scheme of Evolution as we would those of Lucretius or of 

 Lamarck, delighting in their simplicity and their courage. The 

 practical and experimental study of Variation and Heredity has not 

 merely opened a new field ; it has given a new point of view and new 

 standards of criticism. Naturalists may still be found expounding 

 teleological systems * which would have delighted Dr. Pangloss 



* I take the following from the Abstract of a recent Croonian Lecture 

 " On the Origin of Mammals "' delivered to the Royal Society : — "In Upper 

 Triassic times the larger Cynodonts preyed upon the large Anomodont, 

 Konnemeyeria, and carried on their existence so long as these Anomodonts 

 survived, but died out with them about the end of the Trias or in Rha^tic 

 times. The small Cynodonts, having neither small Anomodonts nor small 

 Cotylosaurs to feed on, were forced to hunt the very active long-limbed 

 Thecodonts. The greatly increased activity brought about that series of 

 changes which formed the mammals — the flexible skin with hair, the four- 

 chambered heart and warm blood, the loose jaw with teeth for mastication, 

 an increased development of tactile sensation and a great increase of 

 cerebrum. Not improbably the attacks of the newly-evolved Cynodont or 

 mammaliau type brought about a corresponding evolution in the Pseudosu- 

 chian Thecodonts which ultimately resulted in the formation of Dinosaurs 

 and Birds." Broom, R.. Proc. Roy. Soc. B., 87, p. 88. 



