TROPICAL STUDIES OF EVOLUTION.e

How far Darwin was aided in his formation of the theory of evolution by investigations of tropical nature in the course of his voyage in the 'Beagle ' is rather a moot question ; but there is no doubt whatever of the enormous support afforded to the theory by the work done in tropical regions by other naturalists, notably Wallace and Belt. To any one who con- siders the question carefully, it must seem almost a truism to assert that the best field for inquiry is that in which a rapid growth is most favoured by Nature, and the least trammeled by any other laws save those of Nature herself. Such a field has Mr. Rodway found in the impenetrable forest of British Guiana ; and, as he brings to bear upon his task not only a wide scientific knowledge, but also a con- siderable power of literary expression and exposition, his sketches of tropical life and the theories he deduces from them are unusually valuable and interesting. In attempting to paint for us the interior of that living temple of Nature, its solemn silences, its distant and leafy dome upborne upon innumerable columns, and the bewildering welter of life and death, of vivid beauty and swift decay, that lies within its depths, the author has essayed the impossible, though, we must admit, if any description in words could achieve a success, he has done all that was possible to succeed. But setting aside the difficulty of bringing home to the mind of one who has never seen it, a satisfactory picture of the tropical forest, the author has at least succeeded in giving a lively and most convincing object-lesson of the doctrine of evolution which may be learnt beneath its shade. As he says,— " Here, in the Guiana forest, the evidence for continual de-

• In the Guiana Forest. By James Bodway, F.L.S. London, T. Fisher Unwin.

velopment is beyond question. Every tree, every animal, and every man is a living example of heredity and environment,— natural and sexual selection. The struggle for life and the survival of the fittest can be seen every day in the forest, on the banks of the rivers, among the sedges and grasses of the swamps, along our muddy shores, and in our semi-wild gardens. The man of the forest, when untainted by contact with his more 3ivilisecl cousin, also, like every other animal, shows that evolution is at work to-day as it has been through all past ages."

In the case of man, however, we might remark that the author has little to show in evidence of his development. One of the chief factors in the straggle for existence, density of popula- tion, is here wanting. It is otherwise in the case of vegetable growth, where development is not only continuous but swift :—

" Everything is the outcome of selfishness and energy. Nature has been lavish with her gifts. Both light and moisture have been plenteously bestowed ; yet few trees can get room to assimilate as much of the two latter as they need. The forest is densely populated,—more so, in fact, than any city ever was or could be. There is not room for one in a thousand of the children born therein, so that the fight for standing-room is like that of a crowd at a fête. It follows, therefore, that every possible contrivance to gain a position has been developed, and the result is almost per- fection. The victory, however, has not been to the few, but to the many. One species has progressed on certain lines, but others have not been idle; although the development may be different, in each case the end is almost identical."

The struggle for existence in the forest is largely a struggle for light and air. Out of the innumerable saplings that find a footing on some open space between the giant stems of their parents, it is obvious that only one or two can survive.

The race upwards, towards the light, seems to absorb all their energies. Woe betide those who are left behind in it! The victors, when once they have struggled to a sufficiently lofty post of vantage, begin putting out their side-branches, elbowing each other, and all below them are doomed to dark- ness and death. Nor does the forest tree find enemies and rivals only amongst his own kind. There are other com- petitors for the light of heaven, against whom no strength of growth can prevail. The creeper has no power to rise save by the help of its upright neighbour. When once it has reached the light by crawling up the sturdy stem of its victim, it begins to smother the latter beneath its spreading canopy of leaf and blossom, while, like a gigantic python, it slowly strangles its growth with the compression of its own coils. Even more insidious is the hostility of other plants,

which, like the clusia or wild-fig, attack their host from above

and not from below. The seed of the fig, dropped by a bird -upon the branch of the tallest tree, if it germinates, may live and grow until it has more than taken the place of its former host. Its soft aerial roots which stream downwards to the soil, when once they have taken hold upon the earth, harden into iron bands about the helpless trunk within their grip. The dense, glossy foliage above shuts out the light, and the

strangling cordage of roots below crushes out the life of the tree until nothing is left but the triumphant clusia

embracing the skeleton of what was once, perhaps, the loftiest tower of the forest. Even worse is the parasite—of the same family as the mistletoe, though of a far more monstrous growth—which sucks for its own maintenance the life-giving sap of the tree upon which it falls. It is against these enemies from without, that the palm has learnt to put on its defensive armour.

Not the least interesting chapter of Mr. Rodway's book is that in which he treats of the interdependence of plant and animal life; though some of the illustrations which he offers are a little fanciful. Rather fanciful also is his account of the human denizens of the forest, who, to tell the truth, hardly fit into the scheme of evolution as it is revealed in the case of animal and plant. Nevertheless, the author's description of the Guiana Indian is well worth reading. One statement that he makes is curious in so far as it accounts for one of the

strangest customs of savage life. The Indian usage that bids the father go to bed when a child is born, and allows, the mother to return at once to her household duties, is explained

by a superstition which attaches the spirit of the child to the body of the father :—

" He must not hunt, shoot, or fell trees for some time, because there is an invisible connection between himself and the babe, whose spirit accompanies him in all his wanderings, and might be shot, chopped, or otherwise injured unwittingly. He therefore retires to his hammock, sometimes holding the little one, and receives the congratulations of his friends, as well as the advice of the elder members of the community. If he has occasion to travel, he must not go very far, as the child and spirit might get

tired, and in passing a creek must first lay across it a little bridge, or bebd a leaf into the shape of a canoe for his com- panion."

The author is much exercised to account for the fact that no Indian is called by his name, and fancies that it may be attributed to some superstition which makes the personal name sacred. After all, it is mere conjecture that any such name is given to a child. Indians, he says, become sullen when a stranger persists in plying them with questions on the subject. They might do that, and yet have no name at all. Among many savage peoples anything like a recognised system of nomenclature is quite unknown. Nor can the author find a satisfactory reason for the choice of the cassava, whose root contains a deadly poison, and consequently needs much troublesome preparation, as the Indian's principal breadstuff. But there is more than one kind of mandioca, as it is called in Spanish America, and they do not all contain the same noxious properties. Would it not be possible, then, that the natives began by eating the innocent kind, and were aided by their experience with that food in discovering a method of eliminating the poison of the other variety P The chapter upon the senses of plants is very sug- gestive, and the author opens a curious question when he asks if plants may not be credited with a sense of smell. " It would be a great anomaly to have a perfume distiller without the sense of smell, and we can see no reason why plants should not enjoy the odours they have taken so much care to mann. facture." Why not, indeed P Though, after all, Nature affords many other instances of sic vos non, vobis, besides plants without a sense of smell. Taken altogether, Mr. Rodney's book is a valuable contribution to the reading of the unscientific naturalist and botanist,—to the ordinary man, that is to say, whose interest in natural history is greater than his opportunity of acquiring knowledge. The photographs, however, by which it is illustrated, give one but a very imperfect and inadequate idea of the subjects they are meant to represent.