Mr. Darwin has devoted no small portion of his valuable life to tracing, in two bulky volumes, the Descent of Man. Yet I suppose it is probable that in our narrow anthropinism we should have refused to listen to him had he given us two volumes instead on the Descent of Walnuts. Viewed as a question merely of biological science, the one subject is just as important as the other. But the old Greek doctrine that 'man is the measure of all things' is strong in us still. We form for ourselves a sort of pre-Copernican universe, in which the world occupies the central point of space, and man occupies the central point of the world. What touches man interests us deeply: what concerns him but slightly we pass over as of no consequence. Nevertheless, even the origin and development of walnuts is a subject upon which we may profitably reflect, not wholly without gratification and interest.

This kiln-dried walnut on my plate, which has suggested such abstract cogitations to my mind, is shown by its very name to be a foreign production; for the word contains the same root as Wales and Welsh, the old Teutonic name for men of a different race, which the Germans still apply to the Italians, and we ourselves to the last relics of the old Keltic population in Southern Britain. It means 'the foreign nut,' and it comes for the most part from the south of Europe. As a nut, it represents a very different type of fruit from the strawberry and raspberry, with their bright colours, sweet juices, and nutritious pulp. Those fruits which alone bear the name in common parlance are attractive in their object; the nuts are deterrent. An orange or a plum is brightly tinted with hues which contrast strongly with the surrounding foliage; its pleasant taste and soft pulp all advertise it for the notice of birds or monkeys, as a means for assisting in the dispersion of its seed. But a nut, on the contrary, is a fruit whose actual seed contains an abundance of oils and other pleasant food-stuffs, which must be carefully guarded against the depredations of possible foes. In the plum or the orange we do not eat the seed itself: we only eat the surrounding pulp. But in the walnut the part which we utilise is the embryo plant itself; and so the walnut's great object in life is to avoid being eaten. Accordingly, that part of the fruit which in the plum is stored with sweet juices is, in the walnut, filled with a bitter and very nauseous essence. We seldom see this bitter covering in our over-civilised life, because it is, of course, removed before the nuts come to table. The walnut has but a thin shell, and is poorly protected in comparison with some of its relations, such as the American butternut, which can only be cracked by a sharp blow from a hammer—or even the hickory, whose hard covering has done more to destroy the teeth of New Englanders than all other causes put together, and New England teeth are universally admitted to be the very worst in the world. Now, all nuts have to guard against squirrels and birds; and therefore their peculiarities are exactly opposite to those of succulent fruits. Instead of attracting attention by being brightly coloured, they are invariably green like the leaves while they remain on the tree, and brown or dusky like the soil when they fall upon the ground beneath; instead of being enclosed in sweet coats, they are provided with bitter, acrid, or stinging husks; and, instead of being soft in texture, they are surrounded by hard shells, like the coco-nut, or have a perfectly solid kernel, like the vegetable ivory.

The origin of nuts is thus exactly the reverse side of the origin of fruits. Certain seeds, richly stored with oils and starches for aiding the growth of the young plant, are exposed to the attacks of squirrels, monkeys, parrots, and other arboreal animals. The greater part of them are eaten and completely destroyed by these their enemies, and so never hand down their peculiarities to any descendants. But all fruits vary a little in sweetness and bitterness, pulpy or stringy tendencies. Thus a few among them happen to be protected from destruction by their originally accidental possession of a bitter husk, a hard shell, or a few awkward spines and bristles. These the monkeys and squirrels reject; and they alone survive as the parents of future generations. The more persistent and the hungrier their foes become, the less will a small degree of bitterness or hardness serve to protect them. Hence, from generation to generation, the bitterness and the hardness will go on increasing, because only those nuts which are the nastiest and the most difficult to crack will escape destruction from the teeth or bills of the growing and pressing population of rodents and birds. The nut which best survives on the average is that which is least conspicuous in colour, has a rind of the most objectionable taste, and is enclosed in the most solid shell. But the extent to which such precautions become necessary will depend much upon the particular animals to whose attacks the nuts of each country are exposed. The European walnut has only to defy a few small woodland animals, who are sufficiently deterred by its acrid husk; the American butter-nut has to withstand the long teeth of much more formidable forestine rodents, whom it sets at nought with its stony and wrinkled shell; and the tropical cocos and Brazil nuts have to escape the monkey, who pounds them with stones, or flings them with all his might from the tree-top so as to smash them in their fall against the ground below.

Our own hazel-nut supplies an excellent illustration of the general tactics adopted by the nuts at large. The little red tufted blossoms which everybody knows so well in early spring are each surrounded by a bunch of three bracts; and as the nut grows bigger, these bracts form a green leaf-like covering, which causes it to look very much like the ordinary foliage of the hazel-tree. Besides, they are thickly set with small prickly hairs, which are extremely annoying to the fingers, and must prove far more unpleasant to the delicate lips and noses of lower animals. Just at present the nuts have reached this stage in our copses; but as soon as autumn sets in, and the seeds are ripe, they will turn brown, fall out of their withered investment, and easily escape notice on the soil beneath, where the dead leaves will soon cover them up in a mass of shrivelled brown, indistinguishable in shade from the nuts themselves. Take, as an example of the more carefully protected tropical kinds, the coco-nut. Growing on a very tall palm-tree, it has to fall a considerable distance toward the earth; and so it is wrapped round in a mass of loose knotted fibre, which breaks the fall just as a lot of soft wool would do. Then, being a large nut, fully stored with an abundance of meat, it offers special attractions to animals, and consequently requires special means of defence. Accordingly, its shell is extravagantly thick, only one small soft spot being left at the blunter end, through which the young plant may push its head. Once upon a time, to be sure, the coco-nut contained three kernels, and had three such soft spots or holes; but now two of them are aborted, and the two holes remain only in the form of hard scars. The Brazil nut is even a better illustration. Probably few people know that the irregular angular nuts which appear at dessert by that name are originally contained inside a single round shell, where they fit tightly together, and acquire their queer indefinite shapes by mutual pressure. So the South American monkey has first to crack the thick external common shell against a stone or otherwise; and, if he is successful in this process, he must afterwards break the separate sharp-edged inner nuts with his teeth—a performance which is always painful and often ineffectual.

Yet it is curious that nuts and fruits are really produced by the very slightest variations on a common type, so much so that the technical botanist does not recognise the popular distinction between them at all. In his eyes, the walnut and the coco-nut are not nuts, but 'drupaceous fruits,' just like the plum and the cherry. All four alike contain a kernel within, a hard shell outside it, and a fibrous mass outside that again, bounded by a thin external layer. Only, while in the plum and cherry this fibrous mass becomes succulent and fills with sugary juice, in the walnut its juice is bitter, and in the coco-nut it has no juice at all, but remains a mere matted layer of dry fibres. And while the thin external skin becomes purple in the plum and red in the cherry as the fruits ripen, it remains green and brown in the walnut and coco-nut all their time. Nevertheless, Darwinism shows us both here and elsewhere that the popular distinction answers to a real difference of origin and function. When a seed-vessel, whatever its botanical structure, survives by dint of attracting animals, it always acquires a bright-coloured envelope and a sweet pulp; while it usually possesses a hard seed-shell, and often infuses bitter essences into its kernel. On the other hand, when a seed-vessel survives by escaping the notice of animals, it generally has a sweet and pleasant kernel, which it protects by a hard shell and an inconspicuous and nauseous envelope. If the kernel itself is bitter, as with the horse-chestnut, the need for disguise and external protection is much lessened. But the best illustration of all is seen in the West Indian cashew-nut, which is what Alice in Wonderland would have called a portmanteau seed-vessel—a fruit and a nut rolled into one. In this curious case, the stalk swells out into a bright-coloured and juicy mass, looking something like a pear, but of course containing no seeds; while the nut grows out from its end, secured from intrusion by a covering with a pungent juice, which burns and blisters the skin at a touch. No animal except man can ever successfully tackle the cashew-nut itself; but by eating the pear-like stalk other animals ultimately aid in distributing the seed. The cashew thus vicariously sacrifices its fruit-stem for the sake of preserving its nut.

All nature is a continuous game of cross-purposes. Animals perpetually outwit plants, and plants in return once more outwit animals. Or, to drop the metaphor, those animals alone survive which manage to get a living in spite of the protections adopted by plants; and those plants alone survive whose peculiarities happen successfully to defy the attack of animals. There you have the Darwinian Iliad in a nutshell.