Vol. XXIII. No. 7.] 



POPULAE SCIENCE NEWS. 



99 



will develop into a new plant? It is easv to imagine 

 the fate of the greater number. Some will serve as 

 food for birds or other animals; others will fall on 

 bare rocks, or on streams by which they will be 

 borne to the sea; others will fall on soil already 

 fully occupied by plants; — all these will fail to re- 

 produce new plants. Only a small minority of the 

 seeds, therefore, will find a situation favorable to 

 germination and development. But not even all of 

 these can fulfil their natural destiny, for the seeds of 

 other plants — probably of several difterent species — 

 will have lodged in the same mtuation, and will 

 eagerly sieze upon the soil. Thus there will be a 

 contest for place, — a struggle for existence, — silent, 

 but intense. To this struggle there can be but one 

 outcome — the more thrifty and hardy plants will 

 crowd out the weaker; in other words, the fittest 

 will survive. The point to which special attention 

 is to be given is, that, due to an excessive seed- 

 producing power in plants, a principle of natural 

 selection conies into play, and that the superior — 

 that is, more vigorous, more hardy — are selected, at 

 the expense of the inferior. Under a like cause the 

 same principle operates in the animal kingdom 

 also. 



z. Animals prey upon each other, and both ani- 

 mals and plants have to contend against adverse 

 physical conditions. As an instance, take the case 

 of a herd of deer pursued by a pack of wolves. 

 What condition will determine whether any given 

 deer will escape destruction.' Plainly it is that it 

 shall excel in swiftness in running; for those that 

 lag behind will be overtaken by the wolves, and, 

 while they are being devoured, the swifter-footed 

 ones will escape. Again, take the case of a flock 

 of birds, crossing a sea in time of migration, 

 and meeting with a heavy storm. Here the condi- 

 tion determining whether a given bird will withstand 

 the stress, is that it excel in strength of body; for 

 the weaker will be overcome, \yhile the stronger 

 will reach shore in safety. Or, to take an instance 

 from the vegetable kingdom, supposing a grove of 

 trees struck by a high wind. Those trees having 

 the strongest and most firmly fixed roots will escape 

 being uptorn, while those least firmly rooted will be 

 destroyed. The point to be observed is, that among 

 members of the same species there is variation in re- 

 spect to physical powers, and that in the struggle for 

 existence, a principle of natural .selection is at work, 

 by which, again, the fittest survive — that is, the 

 strongest, fleetest, etc. Among the higher animals, 

 the same thing grows out of variation in powers of 

 intelligence. 



3. Among animals, a struggle often occurs be- 

 tween the males at the tiine of mating, the stronger, 

 of course, becoming the victors. Other analogous 

 but more peaceful forms of rivalry also occur. For 

 instance, among birds the males seek to attract the 

 females by song and by display of plumage. To 

 this form of natural selection Darwin gave the name 

 seiual selection. It is seen at once how sexual selec- 

 tion favors the propagation of only the strongest, 

 or, in the case of birds, those having the most bril- 

 liant colors or producing the most melodious notes. 



4. Most plants require, as a condition for produc- 

 ing seeds, that the ovules of one flower shall be fer- 

 tilized by pollen from another. This is effected 

 largely by insects which visit flowers for their honey 

 or pollen, and thus accidentally carry the latter from 

 flower to flower. Now flowers having bright colors 

 or strong odors are more readily discovered by 

 insects, and hence are more likely to have part in 

 this distribution of pollen. Thus it comes about 

 that species of plants having these qualities are 

 likely to be perpetuated, while others, inconspicuous 

 for colors or odors, tend to extinction. Moreover, I 



among plants of the same species, those producing 

 the largest flowers — since there will be some varia- 

 tion — are likely to be the ones whose seeds will give 

 rise to new plants of that kind. Hence, in any one 

 species, there is a tendency to the production of more 

 conspicuous flowers, and, perhaps, flowers having 

 sweeter odors. Here, then, is another way in which 

 natural selection operates. 



Without adducing further instances, it is seen that 

 natural selection is a principle by which animals 

 and plants having any qualities of superiority are 

 preserved, while others, lacking in these qualities, 

 are dostroved. Whatever favors a plant or animal 

 in competition with others, either of the same or 

 different species, constitutes such a quality of supe- 

 riority. It may be powers of intelligence (in the 

 higher animals), or strength of body, or mere color- 

 ation, etc. This principle, operating in a great va- 

 riety of ways, pervades all oi;ganic nature. 



Heredity in its Relation to Natural Selection. — 

 Some intimation of the important part played by 

 the law of heredity in connection with natural selec- 

 tion was made above in paragraphs 3 and 4. We 

 have now to consider this matter more fully. 



Nothing falls more within common observation 

 than that individual animals transmit their peculiar- 

 ities to their descendants. In the case of plants, the 

 same principle holds true, though less noticeable 

 for individual members. It is upon a knowledge of 

 this principle that particular races, strains, or vari- 

 eties of domesticated animals and cultivated plants 

 are produced. For instance, in this way have been 

 derived one strain of horses remarkable for speed, 

 another for draught, etc., or one variety of wheat 

 superior in size of grain, another in prolificncss of 

 yield, etc. Man, by selecting for propagation the 

 superior members of a species through a series of 

 generations, causes that new and superior strains 

 and varieties shall be produced. Now, just as, 

 under the operation of the law of heredity, particular 

 varieties are produced artificially under man's selec- 

 tion, so in nature, according to the same law, vari- 

 eties, and, in the end, species, are produced by nat- 

 ural selection. 



The relation of heredity to natural selection, then, 

 is this : heredity conserves what natural selection 

 acquires. Natural selection causes that the fittest of 

 any one generation shall be kept alive in the strug- 

 gle for existence ; heredity causes that the qualities 

 that render these fittest shall be passed on to suc- 

 ceeding generations. Thus, under the operation oi 

 the two forces, there is a constant cumulation of 

 superior qualities. 



It is readily seen how natural selection, thus sus- 

 tained by heredity, may be a cause of the evolution 

 of organic lorms. It is certainly true that successive 

 generations of any one species must possess in 

 greater and greater degree those qualities which 

 natural selection seizes upon, and if this progressive 

 change takes place along certain lines, it becomes 

 only a matter of the extent to which the process is 

 carried which determines the derivation of species 

 from species. To illustrate : In the case cited 

 above, of the preservation by natural selection of 

 those individuals ot a herd of deer which excelled in 

 running, their superiority in fleetness may have 

 been due to having slightly longer legs than those 

 which were overtaken by the wolves. Now, if in 

 this species of deer length of limb continued to be 

 the quality seized upon by natural selection, it would 

 come about in the course of a number of generations 

 that a variety of deer (though, as yet, of the same 

 species) having unusually long limbs and greatly 

 excelling in speed would be developed. Animals of 

 this variety would be likely to wander away from 

 their shorter-legged congeners, and thus might 



come to inhabit a region difl^erent in climate, food- 

 supply, and other conditions. Under these changed 

 surroundings, or environment, a further natural 

 selection would take place, superiority in some other 

 bodily quality determining which should survive. 

 These changes would go on progressively, and, in 

 the end, a new species of deer would result. The 

 change in specific character would be facilitated and 

 perhaps conditioned by the variety being separated 

 from the parent stock. 



It is upon considerations such as these that natu- 

 ral selection is set forth as the eflScient cause of or- 

 ganic evolution. That natural selection is a com- 

 petent cause for producing varieties of the same 

 species, is admitted by all, but there is yet some dif- 

 ference of opinion whether in the same way deriva- 

 tion of species from species could take place. The 

 balance of opinion is decidedly in favor of the effi- 

 ciency of natural causes to effect derivation, the 

 chief of these causes being natural selection. 



The writer hopes that the present paper has en- 

 abled the reader to clearly apprehend the truth of 

 the following propositions : 



1. Darwin discovered and virtually demonstrated 

 the existence of a great principle of natural selection 

 pervading the organic kingdom. 



2. He set forth this principle as an explanation 

 of the process by which the evolution of the organic 

 kingdom has been effected. 



3. The evidences of organic evolution are quite 

 apart from the evidences of natural selection as its 

 cause. 



One other concluding remark may be made : 

 Darwin, by offering an hypothesis to explain or- 

 ganic evolution, caused general attention to be given 

 to the theory or scientific doctrine of evolution. 

 Since then, evolution has been the key-note — the 

 guiding idea — to discoveries in almost every depart- 

 ment of knowledge. The theory of evolution, by 

 thus stimulating the intellectual activity of our age, 

 has been, and much more is destined to be, of in- 

 calculable service to mankind. 



Union College, Schenectady, N. Y. 



[The four numbers of the Science News con- 

 taining this valuable and interesting article in full, 

 will be sent to any address on receipt of twenty-five 

 cents.] 



INTERESTING SCIENTIFIC EXHIBITS. 



At the recent conversazione of the Royal Society 

 at Burlington House, given by Professor G. G. 

 Stokes, M. A., president, among the scientific ob- 

 jects of interest exhibited was a new adjunct to the 

 optical lantern, invented by Mr. Eric S. Bruce, and 

 called by him the "electro-graphoscope." It con- 

 sisted of a white lath about an inch wide and iS 

 inches long, which was made to rotate windmill 

 fashion by an electro-magnetic motor; a picture then 

 thrown on the rotating lath by the magic lantern 

 was visible in its entirety, on the principle of the re- 

 tention of vision ; the background some distance 

 behind the lath was also visible, hence the picture 

 cast by the lantern, which was one representing a 

 statue, seemed to stand out in midair. 



Mr. A. W. Clayden exhibited a shallow vessel 

 containing water, with projecting flat horizonial 

 pieces of zinc shaped to represent Europe and 

 America, while the water represented the oceans. 

 Then, by means of a dozen or more small pipes, jets 

 of air were blown over the water in such a manner 

 that all the trade and other regular winds were thus 

 represented ; the result was that the surface of the 

 water took up motions representing the Gulf Stream, 

 the cold current flowing down the coast of Labrador, 

 and that other actual oceanic currents were imi- 

 tated. 



