37° 



C. SKOTTSBERG 



This is pure Lamarckian language. We may say, of course, that change of environ- 

 ment may cause mutations, but our experience tends to prove that only a fraction 

 of I % are valuable, the remainder, if not deleterious, at least indifferent. Mutations, 

 gene losses, hybridization, polyploidy and so forth, all may have their share, but 

 they are only ripples on the surface. No theory has been able to penetrate to 

 the nucleus of the problem. Anyhow we have no reason to think that, in its pro- 

 duction of species and genera, families and orders. Nature has followed other lines 

 in islands than in continents. A prominent Swedish geneticist, after a life-time's 

 speculation on the causes generally accepted as responsible for the "origin of species", 

 rejected all of them; unfortunately he threw the egg away with the shell and con- 

 vinced himself that there had been no evolution at all. He did not, however, 

 revert to an omnipotent creator but invented a new and entirely revolutionary theory; 

 if there ever was a stillborn one, it was this [i86). 



I guess we can take it for granted that no peculiar, outstanding types were 

 created on young volcanic islands, whatever their present faunistic and floristic 

 status may be like. Their basic stock is much older than the rocks and inseparably 

 connected with the great continental faunas and floras. Wallace, however, made a 

 distinction between i.sland and continental history. He emphasized that evolution 

 has required an enormously long time to produce the present status, that from 

 the Cretaceous until now nothing of a revolutionary character had happened, families, 

 genera and in cases even species still living date from early Tertiary at least — 

 but on islands the great period of creation was repeated during the last epochs. 



Finally I shall quote some selected passages from Stebp.INS' book on variation 

 and evolution (257). 



The difterentiation of orders and families of flowering plants through the action of 

 natural selection under present conditions is well-nigh impossible. . . . All the trends 

 leading to the dififerentiation of families of flowering plants probably took place simul- 

 taneously and at a relatively early stage of angiosperm evolution. For instance, both 

 distributional and paleontological evidence indicates that the Compositae, the most highly 

 specialized family of dicotyledons, already existed in the latter part of the Cretaceous 

 period, and distributional evidence indicates a similar age for the most advanced families 

 of monocotyledons, the Orchidaceae and Gramineae. It is likely, therefore, that the 

 major part of angiosperm evolution, involving the principal trends in the modification 

 of the flowers, took place during the Mesozoic era (pp. 501-502). 



The gymnosperms prove, he remarks, that neither great antiquity nor rigid 

 stability necessarily leads to senescence, but here, as in other cases, a stenotopic 

 character has resulted in restricted areas and also in extinction. 



Isolated records excepted — the latest discovery is a palm from a Triassic stratum, 

 if correctly determined — angiospermic fossils are found in greater quantity from 

 younger Cretaceous and then in many surprisingly modern types. Evidence is strong, 

 Stebrins has found, that evolution was rapid during one period and slower during 

 another. At the end of the Cretaceous and the beginning of the Eocene the number 

 of modern types increased rapidly. In eocene deposits in North America and Eurasia 

 "the majority of the species belonged to or closely approximated modern genera" 

 (p. 520). This conclusion, mainly based on leaf impressions, is strengthened by the 



