The evolutionary wisdom of specialization: From the octopus's arms to human locomotion

“ With man, the harmony is perfect, because the functions are specialized, and the organs are all adapted in the same respective directions, the fore ones for prehension, the hinder ones for walking. Beyond our branch of the primates, looking toward its origin, the four limbs all exhibit themselves with the same types, but less affirmed, less precise: all four for prehension, the fore ones more so; all four for walking, the hinder ones more so. The evolution begins after the train of the marsupials, and specializations are made in different directions. ”

“ Food to mouth instead of mouth to food is a much later stage in evolution, a fact which may be recalled when we watch the table manners of certain people. Finally, in man the specialisation reaches its natural limit by the complete liberation of the fore-limbs from the purposes of locomotion—though the crawling gait of a child recalls the base degrees by which we did ascend. ”

“ Why, if man can by patience select variations most useful to himself, should nature fail in selecting variations useful, under changing conditions of life, to her living products? What limit can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature,—favouring the good and rejecting the bad? I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life. The theory of natural selection, even if we looked no further than this, seems to me to be in itself probable. ”

“ Thus the reason of one contemplating nature prompts very different judgments from those dictated by the necessity of the needy, or the desire of the voluptuous; for the former considers what value a thing in itself has in the scale of creation, while necessity considers how it meets its need; reason looks for what the mental light will judge to be true, while pleasure looks for what pleasantly titillates the bodily sense. ”

“ Nature, holding fast to the law of economy, does not even always create a new organ for a new function; she may simply adapt an undifferentiated part to special functions, or she may even convert to other uses an organ already specialised (p. 464) . So, for example, the function of respiration is in the lowest animals diffused indifferently over the whole surface of the body, and only as organisation advances is it localised in special organs, such as gills. Now 199suppose that Nature wishes to adapt a fish, which breathes by gills, to life in the air ”

“ But among insects especially we find colonies of numerous multicellular individuals which may be so rigidly specialized for the performance of certain tasks that we can not avoid the use of terms applied to civilized human groups in describing their differentiation and division of labor. ”

“ The division of labour among the organs in the animal organisation has certain limits, since they are hide-bound to the animal organism, cannot be changed at pleasure, and their number is limited. There is also a limit set for the variety of the functions which an animal organism is capable of performing. It is for instance, impossible that the same limb should serve equally well for holding things, for running and flying, not to speak of other specialisations. ”

“ It was necessary that one hand should be chosen to do the dextrous or more skilled tasks, for the simple reason that exercise develops and perfects function, and one would learn to be more skilled and 'handy' with one hand than with both. ”

“ As exercise of the limbs is necessary to physical development, and the act of perceiving, understanding, and fancying, with actual manipulation of nature, is necessary to intellectual development; so is kindness and justice acted out, to the development of the social and moral nature or conscience. ”

“ Had not exercise been absolutely necessary for our well being, says the elegant Addison, nature would not have made the body so proper for it, by giving such an activity to the limbs, and such a pliancy to every part, as necessarily produce those compressions, extensions, contortions, dilatations, and all other kinds of motion, as are necessary for the preservation of such a system of tubes and glands.
We may, indeed, observe, that nature has never given limbs to any animal, without intending that they should be used. ”

“ For the object of nature was to give these animals an organ which should be serviceable in the way of strength, rather than one that should be useful for any of the other purposes to which necks are subservient.
Continuous with the head and neck is the trunk with the anterior limbs. In man the forelegs and forefeet are replaced by arms and by what we call hands. For of all animals man alone stands erect, in accordance with his godlike nature and essence. ”

“ The study of the limbs is of great importance, because, although it is the special province of the bust to contain the organs of vegetative life, it is the limbs which render it useful. In fact, it is the lower limbs which control our locomotion and the upper limbs which execute the labour of mankind. ”

“ The limbs that take their shape from the muscles of locomotion, and the internal parts concerned in those high vital offices, of which minerals and vegetables are wholly destitute, are examples and proof of the configuration proper to the animal kingdom. The thigh, leg, arm, fore-arm, finger, the neck and shoulders, the chest, and the abdomen meeting it and resting on the pelvic bones, are felt to be beautiful or true to the standard form as they taper or conform to this intuitive life-type. ”

“ But I think that we are more averse to assent on false grounds than to anything else which is contrary to nature. Now of the limbs, that is to say, of the parts of the body, some appear to have been given to us by nature because of the use which, they are of to us, as, for instance, the hands, legs, and feet, and also those internal organs of the body, of which I may leave it to the physicians to explain the exceeding usefulness ”

“ You are aware that locomotion is one of the distinguishing characteristics of living beings, and is indispensable for them in their progress towards perfection. As they require food and drink to supply animal waste, so they require locomotion, in order to approach that which is good for them and in harmony with their nature, and to escape from what is injurious and contrary to their nature. ”

“ For the mere prolongation of life, much else is required, fleet limbs to distance lions, and keen senses, sight, hearing, and smell, to give warning of the approach of human or other hunters, to say nothing of the extra strengthening of muscles and bones which increased size and weight demands. ”

“ We must suppose that by natural selection of miscellaneous variations, the parts of the hind limbs shall be co-adapted to one another, in sizes, shapes, and ratios; that those of the fore limbs shall undergo co-adaptations similar in their complexity, but dissimilar in their kinds ”

“ But how does symmetry contribute to fitness, or why is it necessary?
“All our limbs and organs,” says Payne Knight, “serve us in pairs, and by mutual co-operation with each other: whence the habitual association of ideas has taught us to consider this uniformity as indispensable to the beauty and perfection of the animal form. There is no reason to be deduced from any abstract consideration of the nature of things, why an animal should be more ugly and disgusting for having only one eye, or one ear, than for having only one nose or one mouth ”

“ Simultaneously, through nervous modifications, there have been developments of the sensations, instincts, emotions, and intellectual aptitudes, needed for the appropriate uses of these organs; as we see in caged rodents that exercise their incisors by purposeless gnawing, in gregarious creatures which are miserable if they can not join their fellows, in beavers which, kept in confinement, show their passion for dam-building by heaping up whatever sticks and stones they can find. ”

“ Thus, side by side with the involution movement, we find the evolution movement. In the animal kingdom, it is represented by the persistent but mysterious tendency toward variation; in human history, by the comet-like appearance of the reformer; in art, by the lawless product of genius. All these are factors in the upward world-movement which saves us from the stagnation of the relentless law of habit.
But habits, like systems, have their good side. They enable us to do a vast number of actions with the minimum of attention and the least expenditure of nervous energy. ”

“ In the variability of instinct, also, we find mechanical organization less domineering, and in the study of wasps, to which we have just referred, the one preeminent, unmistakable and ever-present fact is variability. ”

“ Again, it should be remembered that even in our preferences and habits it is only in a few things that one hand, etc., has the greater expertness, accuracy and rapidity. It is often rather a division of functions, a differentiation of ability, than a unique one. In the dextral the left hand does many tasks of as great or greater importance, and with equal or superior skill, as the right. ”

“ In all snakes a great flexibility is abundantly provided for in the construction of ‘these lithe and elegant beings,’ as Rymer Jones in unprejudiced language calls them (p. 724 of the book above quoted) ; ‘the spinal column admits the utmost pliancy of motion in any required direction.’
Though snakes have no limbs externally, ‘the work of hands, feet, and fins is performed by a modification of the vertebral column.’ [64] ‘Except flying, there is no limit to their locomotion,’ said Professor Huxley in his lecture on ‘Snakes,’ a few weeks previously to that of Ruskin, and under the same roof. ”

“ And why has Nature, in the case of certain snakes, placed under the skin bony representatives of the extremities, the movements of those animals being by the use of the ribs, and feet never being wanted?
We may also turn to the vegetable world, and there we find rudimentary organs, excesses and deficiences of development. As Treviranus says, adaptation to the surrounding world may be shaped either by gradual development or by degeneration, which is equally effective. The same organ may be expanded into a compound leaf, or degenerated into a scale. Development can turn a reptile into a bird ”

“ The fact that some animals have the use of their limbs immediately after birth, is due, not to their superiority, since more perfect animals are not so endowed; but to the dryness of the brain, and to the operations proper to such animals being imperfect, so that a small amount of strength suffices them. ”

“ We need another and a wiser and perhaps a more mystical concept of animals. Remote from universal nature, and living by complicated artifice, man in civilization surveys the creature through the glass of his knowledge and sees thereby a feather magnified and the whole image in distortion. We patronize them for their incompleteness, for their tragic fate of having taken form so far below ourselves. And therein we err, and greatly err. For the animal shall not be measured by man. ”