Problems and Concepts of Evolution 17 



and others, the fact so often recorded in nature, that modifications within the 

 phylum and in different minor divisions thereof, the supposed succession of 

 species through successive geological horizons, or over some terrestrial surface, 

 appear to have the relation, one to another, of a series of steps which seem to 

 have moved from the first observed condition to the later one of greater or less 

 complexity, and the fact that in ontogeny the sequence of stages during develop- 

 ment is always uniformly the same, and that this ontogenetic sequence to a 

 greater or less extent parallels that found in phylogenetic series, has led many 

 to postulate a causative agency which maintains organisms in these lines, giving 

 specific end-results. Hence the word "orthogenesis," used descriptively by 

 Haacke, has come to a greater or less extent to designate an unknown but active 

 principle, whose effect is to produce these modifications, one after the other, in 

 an orderly, step-like series. There is no denying the facts of our observation 

 as to the series both in phylogeny, ontogeny, and in the phenomena of distribu- 

 tion, but it is not warranted to personify the unknown agencies which were pro- 

 ductive of these conditions and make the unknown an effective cause. A cause 

 there must be, but that there is a force driving organisms through nature, or an 

 evolution-trend moving towards a goal, or a principle of perfectibility is some- 

 thing which the majority of biologists are unable to believe. As a matter of fact, 

 it is highly improbable that the observed conditions described by the word 

 " orthogenesis " are produced by uniform causes at all, and results that might 

 descriptively be called " orthogenetic " might well be produced by quite hetero- 

 geneous causes. There is no positive evidence, aside from plausible interpreta- 

 tions based upon the hypothesis, that the conditions, placed one after another in 

 paleontology or in distribution, really are in sequence with one another ; nor is 

 it known by exact demonstration in any instance that one arose from the other. 

 The data derived from ontogenesis and the frequent parallelism between onto- 

 genesis and phylogenesis does not signify anything more than the conclusion 

 that like substances react alike imder similar conditions, and that the same 

 reactions follow, under similar conditions, the same sequence of events. In 

 physical nature identical substances and identity of capacities under the same 

 conditions produce identical reactions, and show the same array of sequences; 

 and so I should regard both the ontogenetic and phylogenetic series as merely 

 recurrent operations present in essentially the same substance, and they are not 

 to be interpreted as due to a principle driving organisms through a predeter- 

 mined series of events. The data of orthogenesis are entirely of an observational 

 character, based upon studies in phylogenesis, geographical distribution, and 

 ontogenesis ; but there is no evidence that there are productive forces, or a force 

 at all, apart from the other natural operations, and it is possible to find an 

 explanation for these states which are observed in nature that is in harmony 

 with other aspects of the evolution problem. 



With this array of hypotheses conflicting in principle in some respects and 

 overlapping in others as to the production of species in nature, one is made to 

 wonder whether after all there may not be a common basis upon which they can 

 all be tested and brought into agreement. Each one has its good points as well 

 as its defects, and if a common basis of operation and investigation can be found 

 it will be possible to test the respective propositions of each of the divergent 

 conceptions. 



