Origin of Species Variorum

Comparison with 1866

and similar cases, can we understand the cause of such a wide scale of complexity and of such multifarious means for gaining the same end, both in the case of forms widely remote from each other in affinity, and with forms so closely allied as are the two orchids last described? ↑ It was shown, when we discussed the air-breathing apparatus of certain crustaceans, that the process of adaptation for any purpose may start from two or more forms already differing from each other to a considerable degree, and that in almost all cases the nature of the variability, on which natural selection has to work, will be different; consequently, the final structure gained through natural selection, though serving for the same purpose, will be different. We must also bear in mind that every well-developed organism has already passed through a long course of modification; and that each modified structure tends to be inherited, so that it will not readily be lost, but may be modified again and again. Hence the structure of each part of each species, for whatever purpose used, will be the sum of the many inherited changes, through which that species has passed during its successive adaptations to changed habits and conditions of life.

Although in many cases it is most difficult to conjecture by what transitions an organ could have arrived at its present state; yet, considering that the proportion of living and known forms ... is very small compared with the extinct and unknown forms, I have been astonished how rarely an organ can be named, towards which no transitional grade is known to lead. It certainly is true, that new organs very rarely or never suddenly appear in any class, as if created for some special purpose; as indeed is shown by that old canon in natural history of "Natura non facit saltum." We meet with this admission in the writings of almost every experienced naturalist; .. as Milne Edwards has well expressed it, nature is prodigal in variety, but niggard in innovation. Why, on the theory of Creation, should this be so much variety and so little novelty? Why should all the parts and organs of many independent beings, each supposed to have been separately created for its proper place in nature, be so invariably linked together by graduated steps? Why should not Nature have taken a leap from structure to structure? On the theory of natural selection, we can clearly understand why she should not; for natural selection can act only by taking advantage of slight successive variations; she can never take a sudden leap, but must advance by short and sure though slow steps.

Organs of little apparent Importance, as affected by Natural Selection.

As natural selection acts by life and death,—by .. the preservation of individuals with any favourable variation, and by the destruction of those with any unfavourable deviation of structure,—I have sometimes felt much difficulty in understanding the origin of simple parts, of which the importance does not seem sufficient to cause the preservation of successively varying individuals. I have sometimes felt as much difficulty, though of a very different kind, on this head, as in the case

instances, can we understand the graduated scale of complexity and the multifarious means for gaining the same end. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. The answer no doubt is, as already remarked, that when two forms vary, which already differ from each other .. in some slight degree, the variability will not be of the same exact nature, and consequently the results obtained through natural selection for the same general purpose will not be the same. ↑ We should also bear in mind that every highly developed organism has .. passed through many changes; and that each modified structure tends to be inherited, so that each modification will not readily be quite lost, but may be .. again and again further altered. Hence the structure of each part of each species, for whatever purpose it may serve, is the sum of .. many inherited changes, through which the species has passed during its successive adaptations to changed habits and conditions of life.

Finally then, although in many cases it is most difficult even to conjecture by what transitions .. organs .. have arrived at their present state; yet, considering how small the proportion of living and known forms is to the extinct and unknown, ... I have been astonished how rarely an organ can be named, towards which no transitional grade is known to lead. It certainly is true, that new organs appearing as if created for some special purpose, rarely or never appear in any being;— as indeed is shown by that old, but somewhat exaggerated, canon in natural history of "Natura non facit saltum." We meet with this admission in the writings of almost every experienced naturalist; or as Milne Edwards has well expressed it, Nature is prodigal in variety, but niggard in innovation. Why, on the theory of Creation, should there be so much variety and so little real novelty? Why should all the parts and organs of many independent beings, each supposed to have been separately created for its proper place in nature, be so commonly linked together by graduated steps? Why should not Nature .. take a sudden leap from structure to structure? On the theory of natural selection, we can clearly understand why she should not; for natural selection .. acts only by taking advantage of slight successive variations; she can never take a great and sudden leap, but must advance by short and sure, though slow steps.

Organs of little apparent Importance, as affected by Natural Selection .

As natural selection acts by life and death,— by the survival of the fittest, and by the destruction of the less well-fitted individuals, — I have sometimes felt great difficulty in understanding the origin or formation of parts of little importance; almost as great, though of a very different kind, ... as in the case