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THE INCOMPETENCY OF “NATURAL SELECTION ?’ To ACCOUNT FOR THE INCIPIENT STAGES OF USEFUL STRUCTURES.
. Darwin supposes that Natural Selection acts by Slight Wariations,—These must be useful at once.—Difficulties as to the Giraffe; as to Mimicry; as to the Heads of Flat-fishes; as to the Origin and Constancy of the Wertebrate Limbs; as to Whalebone; as to the Young Kangaroo; as to Sea-urchins; as to certain Processes of Metamorphosis; as to the Mammary-gland; as to certain Ape Characters; as to the Rattlesnake and Cobra; as to the Process of Formation of the Eye and Ear, as to the Fully-developed Condition of the Eye and Ear; as to the Voice; as to Shellfish; as to Orchids; as to Ants.-the Necessity for the Simultaneous Modification of Many Individuals.--Summary and Conclusion.
“NATURAL Selection,” simply and by itself, is potent to explain the maintenance or the further extension and development of favorable variations, which are at once sus. ficiently considerable to be useful from the first to the individual possessing them. But Natural Selection utterly fails to account for the conservation and development of the minute and rudimentary beginnings, the slight and infinitesimal commencements of structures, however useful those structures may afterward become.
Now, it is distinctly enunciated by Mr. Darwin, that the spontaneous variations upon which his theory depends are individually slight, minute, and insensible. He says," “Slight individual differences, however, suffice for the work, and are probably the sole differences which are effective in the production of new species.” And again, after mentioning the frequent sudden appearances of domestic varieties, he speaks of “the false belief as to the similarity of natural species in this respect.” “ In his work on the “Origin of Species,” he also observes, “Natural Selection acts only by the preservation and accumulation of small inherited modifications.”* And “Natural Selection, if it be a true principle, will banish the belief . . . of any great and sudden modification in their structure.” “ Finally, he adds, “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by mumerous, successive, slight modifications, my theory would absolutely break down.”" Now the conservation of minute variations in many instances is, of course, plain and intelligible enough; such e.g., as those which tend to promote the destructive faculties of beasts of prey on the one hand, or to facilitate the flight or concealment of the animals pursued on the other; provided always that these minute beginnings are of such a kind as really to have a certain efficiency, however small, in favor of the conservation of the individual possessing them; and also provided that no unfavorable peculiarity in any other direction accompanies and neutralizes, in the struggle for life, the minute favorable variation. But some of the cases which have been brought forward, and which have met with very general acceptance, seem less satisfactory when carefully analyzed than they at first appear to be. Among these we may mention “the neck of the giraffe.” At first sight it would seem as though a better example in support of “Natural Selection” could hardly have been chosen. Let the fact of the occurrence of occasional severe droughts in the country which that animal has in* “Animals and Plants under Domestication,” vol. ii., p. 414.
* “Animals and Plants under Domestication,” vol. ii., n 192
habited be granted. In that case, when the ground vegetation has been consumed, and the trees alone remain, it is plain that at such times only those individuals (of what we assume to be the nascent giraffe species) which were able to reach high up would be preserved, and would become the parents of the following generation, some individuals of which would, of course, inherit that high-reaching power which alone preserved their parents. Only the high-reaching issue of these high-reaching individuals would again, casteris paribus, be preserved at the next drought, and would again transmit to their offspring their still loftier stature; and so on, from period to period, through aeons of time, all the individuals tending to revert to the ancient shorter type of body, being ruthlessly destroyed at the occurrence of each drought. (1.) But against this it may be said, in the first place, that the argument proves too much ; for, on this supposition, many species must have tended to undergo a similar modification, and we ought to have at least several forms, similar to the giraffe, developed from different Ungulata." A careful observer of animal life, who has long resided in South Africa, explored the interior, and lived in the giraffe country, has assured the author that the giraffe has powers of locomotion and endurance fully equal to those possessed by any of the other Ungulata of that continent. It would seem, therefore, that some of these other Ungulates ought to have developed in a similar manner as to the neck, under pain of being starved, when the long neck of the giraffe was in its incipient stage. To this criticism it has been objected that different kinds of animals are preserved, in the struggle for life, in very different ways, and even that “high reaching” may be attained in more modes than one—as, for example, by the trunk of the elephant. This is, indeed, true, but then none of the African Ungulata" have, nor do they appear ever to have had, any proboscis whatsoever; nor have they acquired such a development as to allow them to rise on their hind-limbs and graze on trees in a kangaroo attitude, nor a power of climbing, nor, as far as known, any other modification tending to compensate for the comparative shortness of the neck. Again, it may perhaps be said that leaf-eating forms are exceptional, and that therefore the struggle to attain high branches would not affect many Ungulates. But surely, when these severe droughts necessary for the theory occur, the ground vegetation is supposed to be exhausted ; and, indeed, the giraffe is quite capable of feeding from off the ground. So that, in these cases, the other Ungulata must have taken to leaf-eating or have starved, and thus must have had any accidental long-necked varieties favored and preserved exactly as the long-necked varieties of the giraffe are supposed to have been favored and preserved. The argument as to the different modes of preservation has been very well put by Mr. Wallace,” in reply to the objection that “color, being dangerous, should not exist in Nature.” This objection appears similar to mine; as I say that a giraffe neck, being needful, there should be many animals with it, while the objector noticed by Mr. Wallace says, “A dull color being needful, all animals should be so colored.” And Mr. Wallace shows in reply how porcupines, tortoises, and mussels, very hard-coated bombadier beetles, stinging insects, and nauseous-tasted caterpillars, can afford to be brilliant by the various means of active defence or passive protection they possess, other than obscure coloration. He says: “The attitudes of some insects may also protect them, as the habit of turning up the tail by the harmless rove-beetles (Staphylinidae), no doubt leads other animals, besides children, to the belief that they can sting. The curious attitude assumed by sphinx caterpillars is probably a safeguard, as well as the blood-red tentacles which can suddenly be thrown out from the neck by the caterpillars of all the true swallow-tailed butterflies.” But, because many different kinds of animals can elude the observation or defy the attack of enemies in a great variety of ways, it by no means follows that there are any similar number and variety of ways for attaining vegetable food in a country where all such food, other than the lofty branches of trees, has been for a time destroyed. In such a country we have a number of vegetable-feeding Ungulates, all of which present minute variations as to the length of the neck. If, as Mr. Darwin contends, the natural selection of these favorable variations has alone lengthened the neck of the giraffe by preserving it during droughts; similar variations, in similarly feeding forms, at the same times, ought similarly to have been preserved and so lengthened the neck of some other Ungulates by similarly preserving them during the same droughts. (2.) It may be also objected, that the power of reaching upward, acquired by the lengthening of the neck and legs, must have necessitated a considerable increase in the entire size and mass of the body (larger bones requiring stronger and more voluminous muscles and tendons, and these again necessitating larger nerves, more capacious bloodvessels, etc.), and it is very problematical whether the disadvantages thence arising would not, in times of scarcity, more than counterbalance the advantages. For a considerable increase in the supply of food would be requisite on account of this increase in size and mass, while at the same time there would be a certain decrease
* The order Ungulata contains the hoofed beasts; that is, all oxen, deer, antelopes, sheep, goats, camels, hogs, the hippopotamus, the different kinds of rhinoceros, the tapirs, horses, asses, zebras, quaggas, etc.
7 The elephants of Africa and India, with their extinct allies, consti, tute the order Proboscidea, and do not belong to the Ungulata. .8 See “Natural Selection,” pp. 60–75.