64 SECTIONAL ADDRESSES 



and still survives ; whereas Diademopsis, a type, so similar as to be almost 

 the despair of systematists, appeared at the same time and failed to 

 outlast the Jurassic period. 



There is also a wide range of difference in the geographical distribution 

 of genera and species, seemingly independent of the time-range. While 

 it is, of course, natural that planktonic forms, such as some of the Grapto- 

 lites, should be drifted far and wide by ocean currents, it must be realised 

 that most marine organisms pass through a planktonic stage in development. 

 Not all of them take advantage of this opportunity for wide dispersion. 

 In view of the uncertainty as to the truly specific identity of fossils that 

 are apparently alike, and of the incidence of orthogenetic and con- 

 vergent trends in morphogeny, the problems raised by the study of palaso- 

 geographical distribution are too hypothetical to be considered here. 



These diversities of quality, in duration and dispersion, of fossil types 

 in all grades of classification are strikingly reminiscent of the differences 

 of longevity and migration that may occur in different individuals of a 

 single species, or even of a single generation born of the same parents. 

 Whatever may be the explanation (and we know the causes of such diver- 

 sity to be infinitely complex in the case of members of our own species), 

 the tendency towards, or capacity for, the differences seems to exist as a 

 general principle throughout living matter. Palaeontology merely shows 

 here that a quality of life with which all of us are personally familiar 

 applies equally in the larger histories in which individuals or generations 

 are but transient incidents. 



In the perspective given by geological time, we may hope to detect 

 some of the outstanding characters that accompany, and perchance in- 

 fluence, the success or failure of a group of organisms. We lose sight of 

 the innumerable trivial accidents that determine the fate of an individual, 

 so that more fundamental tendencies become clearer. In this particular 

 instance we can observe the characters that history has proved to be 

 associated with longevity or its reverse. 



Without enumerating actual cases (which would be tedious for those 

 who know and still more so for those who do not) we can make at least one 

 generalisation that seems to be true. Simplicity of structure, so long as it 

 is combined with reasonable efficiency, is associated with palaeontological 

 longevity; while complexity of structure, however efficient, implies 

 relatively brief duration. We need not at this stage look for a reason for 

 the existence of such qualities, but it is patent that they exist. The 

 reason for their effect, however, is so manifest that it could be adumbrated 

 even if proof were lacking. Any organism must of necessity be in tune 

 with its environment if it is to survive. Elaborate structures can fit only 

 a special type of environment, whereas simple structures have a wider 

 scope of possible harmonies ; just as a chord of many notes is less easily 

 harmonised with another than a single note. In geological time, environ- 

 mental changes are inevitable, so that simple structures will have a better 

 chance of survival than complex ones. The platitudinous nature of this 

 statement is well shown in everyday experience, for the ignorance of a 

 thoroughgoing specialist of any but his peculiar brand of knowledge 

 is notorious. 



