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SCIENCE 



[N. S. Vol. LII. No. 1342 



mountaia limestones, the chalks, and the 

 siliceous earths, but the changes of land and 

 sea would have been far other. To the scien- 

 tific interpreter of earth-history, the impor- 

 tance of fossils lies first in their value as date- 

 markers; secondly, in the light which they 

 cast on barriers and currents, on seasonal and 

 , climatic variation. Conversely, the history of 

 life has itself been influenced by geologic 

 change. But all this is just as true of the pres- 

 ent inhabitants of the globe as it is of their 

 predecessors. It does not give the differentia 

 of paleontology. 



That which above all distinguishes paleon- 

 tology — the study of ancient creatures, from 

 neontology — the study of creatures now liv- 

 ing, that which raises it above the mere de- 

 scription of extinct assemblages of life-forms, 

 is the concept of time. ibTot the quasi-absolute 

 time of the clock, or rather of the sun; not 

 various unrelated durations; but an orderly 

 and related succession, coextensive, in theory 

 at least, with the whole history of life on this 

 planet. The bearing of this obvious statement 

 will appear from one or two simple illustra- 

 tions. 



EFFECT OF THE TIME-CONCEPT ON PRINCIPLES OP 

 CLASSIFICATION 



Adopting the well-tried metaphor, let us 

 imagine the tree of life buried, except for its 

 topmost twigs, beneath a sand-dune. The 

 neontologist sees only the unburied twigs. He 

 recognizes certain rough groupings, and con- 

 structs a classification accordingly. From 

 various hints he may shrewdly infer that some 

 twigs come from one branch, some from 

 another; but the relations of the branches to 

 the main stem are matters of speculation, and 

 when branches have become so interlaced that 

 their twigs have long been subjected to the 

 same external influences, he will probably be 

 led to incorrect conclusions. The paleontolo- 

 gist then comes, shovels away the sand, and 

 by degrees exposes the true relations of 

 branches and twigs. His work is not yet ac- 

 complished, and probably he never will reveal 

 the root and lower part of the tree; but already 



he has corrected many natural, if not inev- 

 itable, errors of the neontologist. 



I could easily occupy the rest of this hour 

 by discussing the profound changes wrought 

 by this conception on our classification. It is 

 not that orders and classes hitherto unknovm 

 have been discovered, not that some erroneous 

 allocations have been corrected, but the whole 

 basis of our system is being shifted. So long 

 as we were dealing with a horizontal section 

 across the tree of life — that is to say, with an 

 assemblage of approximately contemporane- 

 ous forms — or even with a number of such 

 horizontal sections, so long were we confined 

 to simple description. Any attempt to frame 

 a causal connection was bound to be specula- 

 tive. Certain relations of structure, as of 

 cloven hoofs with horns and with a ruminant 

 stomach, were observed, but, as Cuvier himself 

 insisted, the laws based on such facts were 

 purely empirical. Huxley, then, was justified 

 in maintaining, as he did in 1863 and for long 

 after, that a zoological classification could be 

 based with profit on " purely structural con- 

 siderations " alone. " Every group in that 

 [kind of] classification is such in virtue of cer- 

 tain structural characters, which are not only 

 common to the members of that group, but dis- 

 tinguish it from all others; and the statement 

 of these constitutes the definition of the 

 group." In such a classification the groups or 

 categories — from species and genera up to 

 phyla — are the expressions of an arbitrary in- 

 tellectual decision. From Linnseus down- 

 wards botanists and zoologists have sought for 

 a classification that should be not arbitrary 

 but natural, though what they meant by " nat- 

 ural " neither Linnffius nor his successors 

 either could or would say. Not, that is, until 

 the doctrine of descent was firmly established, 

 and even now its application remains imprac- 

 ticable, except in those cases where sufficient 

 proof of genetic connection has been furnished 

 — as it has been mainly by paleontology. In 

 many cases we now perceive the causal con- 

 nection; and we recognize that our groupings, 

 so far as they follow the blood-red clue, are not 

 arbitrary but tables of natural affinity. 



Fresh difficulties, however, arise. Consider 



