312 THE ZOOLOGIST. 



Sheep, Poultry, Wheat, Oats, Eice, Plums, Cherries, have in turn 

 been accepted as " polyphyletic " or, in other words, derived from 

 several distinct forms. The reason that has led to these judgments 

 is that the distinctions between the chief varieties can be traced as 

 far back as the evidence reaches, and that these distinctions are 

 so great, so far transcending anything that we actually know varia- 

 tion capable of effecting, that it seems pleasanter to postpone the 

 difficulty, relegating the critical differentiation to some misty anti- 

 quity into which we shall not be asked to penetrate. For it need 

 scarcely be said that this is mere procrastination. If the origin of a 

 form under domestication is hard to imagine, it becomes no easier to 

 conceive of such enormous deviations from type coming to pass in 

 the wild state. Examine any two thoroughly distinct species which 

 meet each other in their distribution, as, for instance, Lychnis diurna 

 and vespertina do. In areas of overlap are many intermediate forms. 

 These used to be taken to be transitional steps, and the specific 

 distinctness of vespertina and diurna was on that account questioned. 

 Once it is known that these supposed intergrades are merely mongrels 

 between the two species the transition from one to the other is 

 practically beyond our powers of imagination to conceive. If both 

 these can survive, why has their common parent perished ? Why 

 when they cross do they not reconstruct it instead of producing 

 partially sterile hybrids ? I take this example to show how entirely 

 the facts were formerly misinterpreted. 



When once the idea of a true-breeding — or, as we say, homozygous 

 — type is grasped, the problem of variation becomes an insistent 

 oppression. What can make such a type vary ? We know, of 

 course, one way by which novelty can be introduced — by crossing. 

 Cross two well-marked varieties — for instance, of Chinese Primula — 

 each breeding true, and in the second generation by mere recombina- 

 tion of the various factors which the two parental types severally 

 introduced, there will be a profusion of forms, utterly unlike each 

 other, distinct also from the original parents. Many of these can be 

 bred true, and if found wild would certainly be described as good 

 species. Confronted by the difficulty I have put before you, and 

 contemplating such amazing polymorphism in the second generation 

 from a cross in Antirrhinum, Lotsy has lately with great courage 

 suggested to us that all variation may be due to such crossing. I do 

 not disguise my sympathy with this effort. After the blind com- 

 placency of conventional evolutionists it is refreshing to meet so 

 frank an acknowledgment of the hardness of the problem. Lotsy's 

 utterance will at least do something to expose the artificiality of 

 systematic zoology and botany. Whatever might or might not be 

 revealed by experimental breeding, it is certain that without such 

 tests we are merely guessing when we profess to distinguish specific 

 limits and to declare that this is a species and that a variety. The 

 only definable unit in classification is the homozygous form which 

 breeds true. When we presume to say that such and such differences 

 are trivial and such others valid, we are commonly embarking on a 

 course for which there is no physiological warrant. Who could have 



