394 TEE POPULAR SCIENCE MONTHLY 



Darwin and Wallace have talked of the accumulation of small varia- 

 tions, of the effects of natural selection on the perpetual minute varia- 

 tions which all species exhibit. Antiselectionists answer that most of 

 these are non-heritable "fluctuating variations/' and as for the rest, 

 they are usually not small, nor is the variation " continuous." More- 

 over, selection soon gets to the end of its rope. So it seems when we 

 are looking at a single pair, or two or three pairs of Mendelian allelo- 

 morphs, all active independently of one another. This, however, is not 

 a true picture of living animals, which are bundles of uncounted " fac- 

 tors," acting together in various ways. Any single factor depends for 

 its appearance and form of manifestation on all the others, as Wilson 

 has urged. It is not a thing by itself; it is the result of a complex 

 equation. Sometimes we are getting along well enough with our ex- 

 periments, when suddenly things go wrong; not because of error in 

 our theory, but because some new factor, which we were not watching, 

 has come in and disturbed the results. Thus, in breeding red sun- 

 flowers, we predicted, and got, a dark red homozygous flower. We also 

 got, but did not predict, a homozygous red in which only the basal half 

 of each ray was of that color. The fact is that many of the wild sun- 

 flowers carry a factor for marking, which can be seen with difficulty 

 on close inspection, but in the red it comes out strongly. For reasons 

 of this sort we have not only the complications due to the multitude 

 of factors or determiners, but also those caused by their interactions. 

 Inasmuch as they may influence each other strongly or slightly, and 

 in all sorts of different ways, the net result is that in the more complex 

 types of life we have almost infinite possibilities of variation, quite 

 aside from any question of the alteration of the determiners themselves. 

 Add to this the complications due (it appears) to accidents in the 

 maturation process of the germ cells — such an "accident" probably 

 gave rise to the red sunflower — and we have in most cases as much 

 material for natural selection to operate upon as Darwin or Wallace 

 ever postulated. Enough, indeed, to account for all the wonderful 

 adaptations in the tropical fauna and flora, when we consider the time 

 available for their production. 



It has recently been announced, as the result of the museum work 

 of Dr. K. Jordan, combined with the field and breeding observations 

 of Dr. G. D. H. Carpenter, 3 that an African butterfly of the genus 

 Pseudacroea occurs in a variety of forms, which imitate species of 

 Planema flying with it. The extraordinary thing is that one phase of 

 this Pseudacrcea is sexually dimorphic, imitating a dimorphic Planema, 

 while in the same forests it also occurs in two monomorphic forms, 

 resembling two other monomorphic species of Planema. Dr. Carpenter 

 succeeded in breeding one of the monomorphic Pseudacrceas from an 



3 Entomologists' Becord, XXIV. (1912), p. 233. 



