Vol. XXIII. No. 6.] 



POPULAR SCIENCE I^EWS. 



83 



skeletons of these parts, placed side by side, would 

 strikingly show their correspondence. Each would 

 show hones answering to those of the upper arm. 

 lower arm, wrist, palin, and fingers of the arm of 

 man. Or, if parts apparently so diverse as the wing 

 of a bird, the flipper of a seal, and the fore-leg of a 

 tortoise, be compared with one another and with the 

 fore-limbs of the animals just named, all will be 

 seen to l)e made on a common plan. Even the fin 

 of a fish (including the fin-bones) shows homology 

 with the fore-limbs of the other classes of vertebrate 

 animals. It is from studies like these, extending 

 through the whole scale of organic structure, that 

 strong evidences of the common origin of widely 

 divergent types are brought to light. An evolution 

 of the different classes of vertebrate animals (under 

 1(1 uses to be considered later) from that of an ances- 

 tral vertebrate type, is the only way of accounting, 

 under natural causes, for the facts of homology just 

 noticed. 



Evidences of Geology. 



It is well known that the remains of plants and 

 animals that lived in past ages are found in the 

 rocks as fossils. By what seeins to be the mere bv- 

 play of nature's processes, there are preserved to us 

 perfect reproductions in enduring stone of the bodilv 

 forms of living creatures of ages millions of years 

 gone by. Thus there is open to us a record of the 

 liistory of organic nature — a record of absolute reli- 

 ability, and of completeness sufficient to enable us to 

 read with certainty the main lines of the historv. 



These fossils are found in stratified rocks, and, 

 inasmuch as the strata are always super-imposed in 

 order froin oldest to most recent, we have alreadv 

 determined for us the relative ages of the organic 

 remains contained in them. It is evident at once 

 that a study of the fossils, in respect to their grade 

 of organization in its relation to the age of the rock- 

 '■trata in which they are contained, throws light on 

 the question of organic evolution. For if with the 

 passage of time, there was an evolution of succes- 

 sively higher and higher organic forms, then the 

 oldest rocks should contain remains of the lowest 

 organisms, and the rocks formed at successively 

 later periods the remains of forms successively 

 liigher in grade. Now, upon the whole, it is this 

 state of things that the study of the rocks reveals. 

 The doctrine of organic evolution, therefore, stands 

 the test of geology. 



It is to be expected, of course, on the theorv of 

 t volution, that among the ancient animals found in 

 the fossil state, some will be of such a nature as to 

 indicate strongly that they were the ancestors of 

 different groups of animals now living. This is 

 indeed the case. For instance, fossil animals are 

 found possessing in a remarkable degree a combina- 

 tion of the characters of the present classes of birds 

 and reptiles. It is difficult to say whether these 

 animals should be called reptilian birds or avian 

 reptiles. Other fossil types, combining the charac- 

 ters of fishes and reptiles, reptiles and inammals, 

 etc., are found. Only in a few instances has it been 

 l(nmd possible to trace a series of fossil forms from 

 an ancient extinct species to a living species. But 

 tliis is not to be wondered at, since the remains of 

 rocks could not be expected to be complete. In the 

 rases of the horse and the camel, such series have 

 been worked out quite perfectly. It may be accepted 

 as absolutely demonstrated that the horse has been 

 Lvolved from an ancient animal about the size of a 

 ^lieep, and somewhat resembling the modern tapir 

 in its general bodily structure. 



I'.ridences of Geographical Dislrihulion. 



It is a familiar observation of travelers that the 

 jilants and anitnals native to one region of country 

 diflfer from those of another. This is noticeable not 



only in going from warm to cold latitudes, or the 

 reverse, but in going from one region to another of 

 the same latitude. For instance, the native plants 

 of our northern states are not only different from 

 those of the southern states, but also from those of 

 western states having about the same climate. A 

 careful study of the subject has shown that when 

 countries similar in climate have different fauna and 

 flora, there are always geographical barriers, — such 

 as mountain-ranges, seas, and deserts, — preventing 

 communication. For instance, the island of Mada- 

 gascar. \yhich has an animal population strikingly 

 different from that of southern Africa, is cut off from 

 the main land by a broad channel. In the same 

 way, southern Europe, the fauna of which differs 

 from that of northern Africa, is separated from the 

 latter by the Mediterranean Sea. But these differ- 

 ences in the general fauna do not relate to birds or 

 to species capable of being transported by winds or 

 waves. In this connection it may be said that the 

 animals and plants inhabiting mid-ocean islands are 

 alwavs such as are capable of being transported 

 (often in the form of seeds or ova) by natural agen- 

 cies, or, in the case of birds, bats, and insects, by 

 power of flight. 



Now, these facts find an explanation in the theory 

 of evolution. For, if we suppose that organic 

 forms are all the while undergoing slow changes, 

 progressive and divergent, it is seen at once that the 

 inhabitants of countries cut off by geographical bar- 

 riers would, in the course of a long period of time, 

 become very different, exception being made in the 

 case of those having powers to surmount these bar- 

 riers. It is found that, upon the whole, the dissimi- 

 larity of fauna or flora between different regions of 

 like climatic conditions, is in proportion to the 

 length of time (estimated upon geological data) they 

 have been separated, and the degree of impassibility 

 of the separating barrier. 



A single illustration may be added : The island 

 of Australia contains no native mammals except 

 marsupials (the kangaroo class) and bats. Why no 

 others? and, also, why these.' Because this island 

 was separated from the main continent before there 

 were any other mammals than marsupials. Other 

 classes of mammals have been evolved since, but 

 elsewhere than in Australia, and none of them could 

 get there except bats, these being the only mammals 

 that have the power of extensive flight. The kan- 

 garoo class became inhabitants of the region when 

 it was connected with the main land, and when that 

 class was dominant throughout the eastern conti- 

 nent. When the island was formed, its inhabitants, 

 becoming imprisoned there, escaped the destruction 

 that befell their congeners on the continent, in the 

 strife for existence with the larger and more power- 

 ful mammalia that followed. But that the original 

 marsupials of Australia were not absolved by their 

 isolation from the edict of evolution, is shown by 

 the very large number of distinct species and also 

 genera now found there. 



Evidences of Embryology. 



The study of embryology — the developinent of the 

 individual animal or plant — gives strong corrobora- 

 tion to the conclusions arrived at by investigations 

 along the several lines of inquiry just considered. 

 It is found that the stages through which an animal 

 passes in its individual development, are such as, it 

 is assumed under the theory of evolution, the class 

 to which the animal belongs passed through in its 

 development. To watch the development of a chick 

 through a period of a few weeks (this is practically 

 possible) is, therefore, to see in recapitulation the 

 development of the class of birds through the long 

 jjeriods of geologic time. It is certainly entirely 

 true that the stages through which the chick passes 



in its development form a series which is exactly 

 similar to a series of type-forms of the principal ani- 

 mal groups, taken in order, from the lowest group 

 to the bird group. Now it is just such type-forms 

 that we should expect would succeed one another in 

 the evolution of the animal kingdom, — each in turn 

 being a centre from which was evolved ultimately 

 the multitude of specific forms making up a great 

 animal group. To put the matter in another way, 

 it is probable that type-forms of the zoological 

 groups, taken in order from lowest to highest, 

 represent the succession of type-fonns in the evolu- 

 tion of the animal kingdom. But each animal, in 

 its individual development, or embryology, shows a 

 similar succession of forms. Hence, the conclusion 

 of modern biology : The history of the individual is 

 an epitome of the history of its class. This is one 

 of the broadest and grandest generalizations of 

 science. 



The evidence afforded by embryology, then, tends 

 strongly to confirm the conclusion pointed to by 

 the several classes of facts illustrated above. Com- 

 parative anatomy, geology, and geographical distri- 

 bution bring forward a multitude of facts which find 

 their only explanation in a theory of evolution. 

 Embryology shows that such an evolution actually 

 does take place, in epitome, in the development of 

 the individual organism. 



If, on these grounds, it be concluded that organic 

 evolution is true, it still remains to explain the 

 causes of evolution. We have seen that social insti- 

 tutions are evolved by human agencies ; that the 

 earth and the cosmos have been evolved by the 

 agency of natural forces ; by what agencies has the 

 organic kingdom been evolved.' This question we 

 will consider in the next paper. 



One other point may be referred to here. Any 

 discussion of organic evolution (as intimated above) 

 must begin by assuming the existence of certain 

 primordial forms of life. Whence came these forms .' 

 It can only be said that to this question science 

 makes no answer. We have no knowledge of any 

 natural process by which living organisms are cre- 

 ated. But this question really forms no part of the 

 general question of organic evolution. It must be 

 remembered (see first paper) that evolution does not 

 seek to explain the origination, but the formation, 

 of things. 



Union College, Schenectady, N. Y. 



^^i^ 



[Original in The Popular Science Wcws.J 



A SHORT STUDY IN GEOLOGY. 



BY SAMUEL BRAZIER. 



When, emerging from his pre-savage state, man 

 had acquired the use of his reflective faculties, his 

 observation would be attracted, notonly by the powers 

 and phenomena which nature exhibits by day, but, 

 when the glare of day was succeeded by the solemn 

 gloom of night, the glittering constellations of the 

 starry heavens invited his upward gaze, exciting his 

 wondering admiration and trembling awe. Age 

 after age passes silently away, during which the un- 

 tutored vision of the savage is turned irresisliblv to 

 to the shining orbs of the midnight sky. Millenni- 

 ums roll by, and watchers on the plains of Babylon, 

 Chaldean shepherds, Indian and Egyptian priests, 

 keep up their endless vigils. Then, in later ages, 

 when science dawned on Europe, Ptolemy and 

 Tycho Brahe, Copernicus and Galileo, Kepler and 

 Newton, directed the highest powers of the human 

 intellect to the solution of those problems which the 

 shining heavens present. 



It could not be otherwise. From the dawn of the 

 human intellect, through all ages, the magnificence 

 of the star-lit sky must attract the ignorant wonder 

 or intelligent inquiries of man. But it required the 

 slow and painful march of long ages of barbarism 



