The Birth-Time of the World and Other Scientific Essays Part 11

If the bloom of these higher alpine flowers is especially pleasing to our own aesthetic instincts, and markedly conspicuous to us as observers, why not also especially attractive and conspicuous to the insect whose mission it is to wander from flower to flower over the pastures? The answer to this question involves the hypothesis I would advance as accounting for the bright colours of high-growing individuals. In short, I believe a satisfactory explanation is to be found in the conditions of insect life in the higher alps.

In the higher pastures the summer begins late and

[1] The summer of 1892.

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closes early, and even in the middle of summer the day closes in with extreme cold, and the cold of night is only dispelled when the sun is well up. Again, clouds cover the heights when all is clear below, and cold winds sweep over them when there is warmth and shelter in the valleys. With these rigorous conditions the pollinating insects have to contend in their search for food, and that when the rival attractions of the valleys below are so many.

I believe it is these rigorous conditions which are indirectly responsible for the bright colours of alpine flowers. For such conditions will bring about a comparative scarcity of insect activity on the heights; and a scarcity or uncertainty in the action of insect agency in effecting fertilization will intensify the compet.i.tion to attract attention, and only the brightest blooms will be fertilized.[1]

This will be a natural selection of the brightest, or the

[1] Grant Allen, I have recently learned, advances in _Science in Arcady_ the theory that there is a natural selective cause fostering the bright blooms of alpines. The selective cause is, however, by him referred to the greater abundance of b.u.t.terfly relatively to bee fertilizers. The former, he says, display more aesthetic instinct than bees. In the valley the bees secure the fertilization of all. I may observe that upon the Fridolins Alp all the fertilizers we observed were bees. I have always found b.u.t.terflies very scarce at alt.i.tudes of 7,000 to 8,000 feet. The alpine bees are very light in body, like our hive bee, and I do not think rarefaction of the atmosphere can operate to hinder its ascent to the heights, as Grant Allen suggests. The observations on the death-rate of bees and b.u.t.terflies on the glacier, to be referred to presently, seem to negative such a hypothesis, and to show that a large preponderance of bees over b.u.t.terflies make their way to the heights.

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brightest will be the fittest, and this condition, along with the influence of heredity, will encourage a race of vivid flowers. On the other hand, the more scant and uncertain root supply, and the severe atmospheric conditions, will not encourage the grosser struggle for existence which in the valleys is carried on so eagerly between leaves and branches--the normal offensive and defensive weapons of the plant--and so the struggle becomes refined into the more aesthetic one of colour and brightness between flower and flower. Hence the scant foliage and vivid bloom would be at once the result of a necessary economy, and a resort to the best method of securing reproduction under the circ.u.mstances of insect fertilizing agency. Or, in other words, while the luxuriant growth is forbidden by the conditions, and thus methods of offence and defence, based upon vigorous development, reduced in importance, it would appear that the struggle is mainly referred to rivalry for insect preference. It is probable that this is the more economical manner of carrying on the contest.

In the valleys we see on every side the struggle between the vegetative organs of the plant; the soundless battle among the leaves and branches. The blossom here is carried aloft on a slender stem, or else, taking but a secondary part in the contest, it is relegated to obscurity (P1. XII.). Further up on the mountains, where the conditions are more severe and the supplies less abundant, the leaf and branch a.s.sume lesser dimensions, for they are costly weapons to provide and the elements are unfriendly

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to their existence (Pl. XIII.). Still higher, approaching the climatic limit of vegetable life, the struggle for existence is mainly carried on by the aesthetic rivalry of lowly but conspicuous blossoms.

As regards the conditions of insect life in the higher alps, it came to my notice in a very striking manner that vast numbers of such bees and b.u.t.terflies as venture up perish in the cold of night time. It appears as if at the approach of dusk these are attracted by the gleam of the snow, and quitting the pastures, lose themselves upon the glaciers and firns, there to die in hundreds. Thus in an ascent of the Todi from the Fridolinshute we counted in the early dawn sixty-seven frozen bees, twenty-nine dead b.u.t.terflies, and some half-dozen moths on the Biferten Glacier and Firn. These numbers, it is to be remembered, only included those lying to either side of our way over the snow, so that the number must have mounted up to thousands when integrated over the entire glacier and firn. Approaching the summit none were found. The bees resembled our hive bee in appearance, the b.u.t.terflies resembled the small white variety common in our gardens, which has yellow and black upon its wings. One large moth, striped across the abdomen, and measuring nearly two inches in length of body, was found. Upon our return, long after the sun's rays had grown strong, we observed some of the b.u.t.terflies showed signs of reanimation. We descended so quickly to avoid the inconvenience of the soft snow that we had time for no

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close observation on the frozen bees. But dead bees are common objects upon the snows of the alps.

These remarks I noted down roughly while at Linthal last summer, but quite recently I read in Natural Science[1] the following note:

"Late Flowering Plants.--While we write, the ivy is in flower, and bees, wasps, and flies are jostling each other and struggling to find standing-room on the sweet-smelling plant. How great must be the advantage obtained by this plant through its exceptional habit of flowering in the late autumn, and ripening its fruit in the spring. To anyone who has watched the struggle to approach the ivy-blossom at a time when nearly all other plants are bare, it is evident that, as far as transport of pollen and cross-fertilization go, the plant could not flower at a more suitable time. The season is so late that most other plants are out of flower, but yet it is not too late for many insects to be brought out by each sunny day, and each insect, judging by its behaviour, must be exceptionally hungry.

"Not only has the ivy the world to itself during its flowering season, but it delays to ripen its seed till the spring, a time when most other plants have shed their seed, and most edible fruits have been picked by the birds. Thus birds wanting fruit in the spring can obtain little but ivy, and how they appreciate the ivy berry is evident

[1] For December, 1892, vol. i., p. 730.

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by the purple stains everywhere visible within a short distance of the bush."

These remarks suggest that the ivy adopts the converse att.i.tude towards its visitors to that forced upon the alpine flower. The ivy bloom is small and inconspicuous, but then it has the season to itself, and its inconspicuousness is no disadvantage, _i.e._ if one plant was more conspicuous than its neighbours, it would not have any decided advantage where the pollinating insect is abundant and otherwise unprovided for. Its dark-green berries in spring, which I would describe as very inconspicuous, have a similar advantage in relation to the necessities of bird life.

The experiments of M. C. Flahault must be noticed. This naturalist grew seeds of coloured flowers which had ripened in Paris, part in Upsala, and part in Paris; and seed which had ripened in Upsala, part at Paris, and part at Upsala. The flowers opening in the more northern city were in most cases the brighter.[1] If this observation may be considered indisputable, as appears to be the case, the question arises, Are we to regard this as a direct effect of the more rigorous climate upon the development of colouring matter on the blooms opening at Upsala?

If we suppose an affirmative answer, the theory of direct effect by sun brightness must I think be abandoned. But I venture to think that the explanation of the Upsala

[1] Quoted by De Varigny, _Experimental Evolution_, p. 56.

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experiment is not to be found in direct climatic influence upon the colour, but in causes which lie deeper, and involve some factors deducible from biological theory.

The organism, as a result of the great facts of heredity and of the survival of the fittest, is necessarily a system which gathers experience with successive generations; and the princ.i.p.al lesson ever being impressed upon it by external events is economy. Its success depends upon the use it makes of its opportunities for the reception of energy and the economy attained in disposing of what is gained.

With regard to using the pa.s.sing opportunity the entire seasonal development of life is a manifestation of this att.i.tude, and the fleetness, agility, etc., of higher organisms are developments in this direction. The higher vegetable organism is not locomotory, save in the transferences of pollen and seed, for its food comes to it, and the necessary relative motion between food and organism is preserved in the quick motion of radiated energy from the sun and the slower motion of the winds on the surface of the earth. But, even so, the vegetable organism must stand ever ready and waiting for its supplies. Its molecular parts must be ready to seize the prey offered to it, somewhat as the waiting spider the fly. Hence, the plant stands ready; and every cloud with moving shadow crossing the fields handicaps the shaded to the benefit of the unshaded plant in the adjoining field. The open bloom

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is a manifestation of the generally expectant att.i.tude of the plant, but in relation to reproduction.

As regards economy, any principle of maximum economy, where many functions have to be fulfilled, will, we may very safely predict, involve as far as possible mutual helpfulness in the processes going on. Thus the process of the development towards meeting any particular external conditions, A, suppose, will, if possible, tend to forward the development towards meeting conditions B; so that, in short, where circ.u.mstances of morphology and physiology are favourable, the ideally economical system will be attained when in place of two separate processes, a, , the one process y, cheaper than a + , suffices to advance development simultaneously in both the directions A and B. The economy is as obvious as that involved in "killing two birds with the one stone"--if so crude a simile is permissible--and it is to be expected that to foster such economy will be the tendency of evolution in all organic systems subjected to restraints as those we are acquainted with invariably are.

Such economy might be simply ill.u.s.trated by considering the case of a reservoir of water elevated above two hydraulic motors, so that the elevated ma.s.s of water possessed gravitational potential. The available energy here represents the stored-up energy in the organism. How best may the water be conveyed to the two motors [the organic systems reacting towards conditions A and B] so

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that as little energy as possible is lost in transit? If the motors are near together it is most economical to use the one conduit, which will distribute the requisite supply of water to both. If the motors are located far asunder it will be most economical to lay separate conduits. There is greatest economy in meeting a plurality of functions by the same train of physiological processes where this is consistent with meeting other demands necessitated by external or internal conditions.

But an important and obvious consequence arises in the supply of the two motors from the one conduit. We cannot work one motor without working the other. If we open a valve in the conduit both motors start into motion and begin consuming the energy stored in the tank. And although they may both under one set of conditions be doing useful and necessary work, in some other set of conditions it may be needless for both to be driven.

This last fact is an ill.u.s.tration of a consideration which must enter into the phenomenon which an eminent biologist speaks of as physiological or unconscious "memory,"[1] For the development of the organism from the ovum is but the starting of a train of interdependent events of a complexity depending upon the experience of the past.

[1] Ewald Hering, quoted by Ray Lankaster, _The Advancement of Science_, p. 283.

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In short, we may suppose the entire development of the plant, towards meeting certain groups of external conditions, physiologically knit together according as Nature tends to a.s.sociate certain groups of conditions. Thus, in the case in point, climatic rigour and scarcity of pollinating agency will ever be a.s.sociated; and in the long experience of the past the most economical physiological att.i.tude towards both is, we may suppose, adopted; so that the presence of one condition excites the apparent unconscious memory of the other. In reality the process of meeting the one condition involves the process and development for meeting the other.

And this consideration may be extended very generally to such organisms as can survive under the same a.s.sociated natural conditions, for the history of evolution is so long, and the power of locomotion so essential to the organism at some period in its life history, that we cannot philosophically a.s.sume a local history for members of a species even if widely severed geographically at the present day. At some period in the past then, it is very possible that the individuals today thriving at Paris, acquired the experience called out at Upsala. The perfection of physiological memory inspires no limit to the date at which this may have occurred--possibly the result of a succession of severe seasons at Paris; possibly the result of migrations --and the seed of many flowering plants possess means of migration only inferior to those possessed by the flying and swimming animals. But, again, possibly the experi-

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ence was acquired far back in the evolutionary history of the flower.[1]

But a further consideration arises. Not only at each moment in the life of the individual must maximum income and most judicious expenditure be considered, but in its whole life history, and even over the history of its race, the efficiency must tend to be a maximum. This principle is even carried so far that when necessary it leads to the death of the individual, as in the case of those organisms which, having accomplished the reproductive act, almost immediately expire. This view of nature may be repellent, but it is, nevertheless, evident that we are parts of a system which ruthlessly sacrifices the individual on general grounds of economy. Thus, if the curve which defines the mean rate of reception of energy of all kinds at different periods in the life of the organism be opposed by a second curve, drawn below the axis along which time is measured, representing the mean rate of expenditure of energy on development, reproduction, etc. (Fig. 7), this latter curve, which is, of course,

[1] The blooms of self-fertilising, and especially of cleistogamic plants (_e.g._ Viola), are examples of unconscious memory, or unconscious "a.s.sociation of ideas" leading to the development of organs now functionless. The _Pontederia cra.s.sipes_ of the Amazon, which develops its floating bladders when grown in water, but aborts them rapidly when grown on land, and seems to retain this power of adaptation to the environment for an indefinite period of time, must act in each case upon an unconscious memory based upon past experience. Many other cases might be cited.

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physiologically dependent on the former, must be of such a nature from its origin to its completion in death, that the condition is realized of the most economical rate of expenditure at each period of life.[1] The rate of expenditure of energy at any period of life is, of course, in such a curve defined by the slope of the curve towards the axis of time at the period in question; but this particular slope _must be led to by a previous part of the curve, and involves its past and future course to a very great extent_.

{Fig. 7}

There will, therefore, be impressed upon the organism by the factors of evolution a unified course of economical expenditure completed only by its death, and which will give to the developmental progress of the individual its prophetic character.

In this way we look to the unified career of each organic unit, from its commencement in the ovum to the day