Evolution

164

SOME LOCAL PLANT-GALLS.

ARACHNIDA are represented by the Gall-mites* :—Eriophyes rudis, Canest, causes frequent Witches Brooms on birch.

E. brevitarsus, Nal., and E. laevis, Nal., are both widespread on alder. E. galii, Karp., was first discovered in early May by Mr. Rumbelow on Galium aparine, L., in which Situation it occurs here in all hedgerow areas throughout the summer. E. ribis, Nal., is still fairly frequent, despite the Board of Agriculture's strictures, causing " big b u d " in black-currant bushes.

E. macrorhynchvs, Nal., is present on nearly every maple.

E. similis, Nal., is widespread on sloe ; and E. tatanothrix, Nal., frequent on goat sallow. Phyllocoptes acericola, Nal., abounds on sycamore leaves ; and P. fraxini, Nal., on ash, particularly in damp situations.

EVOLUTION.

BY ERNEST A . ELLIOTT, F . Z . S . , F . E . S . ,

&c.

means development. Now it is evident, that whatever is to be developed, must be already in existence ; hence Evolution has nothing to say as to the origin of life.

Briefiy stated, the Theory is : all existing forms of life have been developed out of earlier forms. It has been both misunderstood and misrepresented. At one time Atheists hoped by means of it to disprove the existence of a Creator. Evolution practically demands a Creator to produce the original germ of life. Some asked, " Have you ever seen such development ? " ; others again asked, " Have you ever known a dog develop into a cat, or a lion into a tiger ? " As to the first of these we reply, that Evolution is the work of countless years ; to the second the answer is, that the existing forms are the ends of many branching radii whereof, could we trace them sufficiently far back, we should find the point whence they have diverged. For examples of Evolution we may point to the numerous varieties of horses, cattle, dogs, poultry or pigeons, on the production of which man has simply taken a page from the book of Nature.

EVOLUTION

T h e saying that " Like produces like " is true only in a limited sense. Man reproduces man, animal reproduces animal, but there are individual differences. It is rare in a human family to find two children exactly alike ; and so, throughout the animate world, there are individual differences. These may be so slight as to be negligible, or so great as to be advantageous or otherwise to the individual. Great strength or power of endurance may *A species of these Gall-mites (Phytoptidae), Tetranychus tiliarum, M ü l l . , was f o u n d to be swarming on L i m e trees at Nettlestead High Hall in 1929 by o u r M e m b e r , M r . W h i t e - C o o p e r . — E d .

EVOLUTION.

165

enable the individual to survive in the struggle for existence, when those less gifted in these respects perish. Weakness or deformity would handicap the victim in the struggle : and this struggle for existence is a very real thing. In the dense woods trees struggle upwards towards the light, forming a covering which cuts off air and sunlight from the ground ; hence only such plants can live on the ground as can endure subdued light, stagnant heat and moisture.

In the Tropics many climbing plants twine round the stems of tall trees, eventually reaching the light, where they flower profusely. Every living creature seeks food ; the strengest come off best. Everything depends on how far each is able to accommodate itself to its surroundings, correspond to its environment. Those which best achieve this will survive, and this is spoken of as " survival of the fittest." Such will transmit to their offspring those qualities which enabled them to survive ; and these qualities, graduaUy increasing, will eventually produce something differing greatly from the original type. " Natural Selection " is the term used to describe the Operation of Nature in favouring those which best correspond to their environment.

Man has taken advantage of these small differences and, by selecting and breeding from them, has produced all the varieties we now see under cultivation. The process, however, is nonnatural selection. Were man's sheltering care withdrawn, these varieties could not persist. Among pigeons, for instance, the more conspicuous and the clumsy flyers would soon fall victims to birds of prey ; ground feeders would be carried off by ground vermin ; few would be able to feed themselves in a natural way, and these few would soon be forced to revert to the original wild type.

In early geological times the surface of our earth was constantly undergoing changes : mountains rose and sank ; continents arose and subsided ; climates altered, and each fluctuation necessitated corresponding changes in such forms of life as succeeded in surviving. Hence Evolution was then active. At the present time, our earth appears to have attained a great measure of stability ; the existing forms are those which have shown themselves best adapted to existing conditions : Evolution may, therefore, be said to be now almost at a stand-still. Such slight modifications as have been noted are due to the interference of man ; for instance, certain moths, after living in smoky towns, are found to become darker in colour.

It must be borne in mind, that Evolution may proceed both upwards and downwards, the latter process being called degeneration. An interesting example of progressive development can be traced from the straight shell of the Orthoceratite from the "ilurian, through the hooked Hamites, to the much-curled

166

EVOLUTION.

Ammonites of the Triassic strata. On the other hand, certain creatures living in dark caverns have lost the use of their eyes, which would be no longer of any service to them. No doubt nature has compensated them for this loss by sharpening other senses. These creatures continue able to exist because they have become adapted to their environment.

One theory supposes that life originated, or was first created, in the sea in the form of a simple cell, gifted with the power of reproduction : other cells, detached from the parent cell, were carried by ocean currents into many differing conditions and accordinglv developed in different ways. It is not possible to trace the steps of the earliest development, but every one of the earlier fossil remains belongs to marine organisms, gradually rising in complexity of Organization. Excepting rare instances, Fishes appear first in the Old Red Sandstone. T o them succeed the Amphibians which, becoming more and more accustomed to terrestrial life, gave us the Reptiles and other land animals.

Birds appear to have evolved from saurian reptiles. An interesting theory traces them to members of Pseudosuchia, a genus of terrestrial Lizards. These reptiles, with progressive frequency, raised the fore part of the body from the ground, moving about on the hind feet only; they then became arboreal climbers, leaping from bough to bough, from tree to tree and to the ground ; and the first toe changed to a hind toe in order to grip the branches, the hind legs being kept close to the body when leaping. The pressure of the air produced, chiefly on the fore limbs and tail, a parachute plane consisting of longish scales, developing along the posterior edges of the forearm and the side edges of the flattened tail. By the friction of the air, the outer edges of the scales become frayed, the frayings changing into still longer processes, becoming more feather-like until the perfect feather is produced. From tail, arms and flanks of the Proavian, the feathering spreads over the whole body : and thus the Reptile, through ages and innumerable generations, has evolved into a Bird.

Great bodily development and brain power do not seem to go together ; in fact all creatures of former ages, that possessed enormous bulk, appear to have had small wits. It may be objected that the Elephant, the largest of living creatures, is also the most intelligent; but the recent elephant is small when compared with Mastodon and Mammoth. Tt would almost appear that the vital forces, concentrated on the brain, can more easily control a smaĂźer body. And mentality must eventually control our Earth ; for, as long as it retains its present surface and climate, there can be but little scope for Natural Selection, because the existing forms correspond with their environment and there is no need for further drastic modification.