Essay Of 1842

[Editor's note: This rough draft of an essay was never published, but was found among Darwin's papers after his death.  Passages which were crossed out in Darwin's original hand-written manuscript are reproduced here in strike-out letters]

PART I  

On Variation under Domestication, and on the Principles of Selection.

 An individual organism placed under new conditions often sometimes varies in a small degree and in very trifling respects such as stature, fatness, sometimes colour, health, habits in animals and probably disposition. Also habits of life develop certain parts. Disuse atrophies. Most of these slight variations tend to become hereditary.

When the individual is multiplied for long periods by buds the variation is yet small, though greater and occasionally a single bud or individual departs widely from its type (example) and continues steadily to propagate, by buds, such new kind.

When the organism is bred for several generations under new or varying conditions, the variation is greater in amount and endless in kind especially holds good when individuals have long been exposed to new conditions. The nature of the external conditions tends to effect some definite change in all or greater part of offspring—little food, small size—certain foods harmless &c. &c. organs affected and diseases—extent unknown. A certain degree of variation (Müller's twins) seems inevitable effect of process of reproduction. But more important is that simple generation, especially under new conditions when no crossing causes infinite variation and not direct effect of external conditions, but only in as much as it affects the reproductive functions. There seems to be no part (beau ideal of liver) of body, internal or external, or mind or habits, or instincts which does not vary in some small degree and often some to a great amount.

All such variations being congenital or those very slowly acquired of all kinds decidedly evince a tendency to become hereditary, when not so become simple variety, when it does a race. Each parent transmits its peculiarities, therefore if varieties allowed freely to cross, except by the chance of two characterized by same peculiarity happening to marry, such varieties will be constantly demolished. All bisexual animals must cross, hermaphrodite plants do cross, it seems very possible that hermaphrodite  animals do cross—conclusion strengthened: ill effects of breeding in and in, good effects of crossing possibly analogous to good effects of change in condition.

Therefore if in any country or district all animals of one species be allowed freely to cross, any small tendency in them to vary will be constantly counteracted. Secondly reversion to parent form—analogue of vis medicatrix. But if man selects, then new races rapidly formed—of late years systematically followed—in most ancient times often practically followed. By such selection make race-horse, dray-horse—one cow good for tallow, another for eating &c.—one plant's good lay «illegible» in leaves another in fruit &c. &c.: the same plant to supply his wants at different times of year. By former means animals become adapted, as a direct effect to a cause, to external conditions, as size of body to amount of food. By this latter means they may also be so adapted, but further they may be adapted to ends and pursuits, which by no possibility can affect growth, as existence of tallow-chandler cannot tend to make fat. In such selected races, if not removed to new conditions, and if preserved from all cross, after several generations become very true, like each other and not varying. But man selects only what is useful and curious—has bad judgment, is capricious—grudges to destroy those that do not come up to his pattern—has no knowledge power of selecting according to internal variations—can hardly keep his conditions uniform—cannot does not select those best adapted to the conditions under which the form lives, but those most useful to him. This might all be otherwise.

II.  On Variation in a State of Nature and on the Natural Means of Selection.

Let us see how far above principles of variation apply to wild animals. Wild animals vary exceedingly little—yet they are known as individuals. British Plants, in many genera number quite uncertain of varieties and species: in shells chiefly external conditions. Primrose and cowslip. Wild animals from different countries can be recognized. Specific character gives some organs as varying. Variations analogous in kind, but less in degree with domesticated animals—chiefly external and less important parts.

Our experience would lead us to expect that any and every one of these organisms would vary if the organism were taken away and placed under new conditions. Geology proclaims a constant round of change, bringing into play, by every possible change of climate and the death of pre-existing inhabitants, endless variations of new conditions. These generally very slow, doubtful though «illegible» how far the slowness would produce tendency to vary. But Geologists show change in configuration which, together with the accidents of air and water and the means of transportal which every being possesses, must occasionally bring, rather suddenly, organism to new conditions and expose it for several generations. Hence we should expect every now and then a wild form to vary; possibly this may be cause of some species varying more than others.

According to nature of new conditions, so we might expect all or majority of organisms born under them to vary in some definite way. Further we might expect that the mould in which they are cast would likewise vary in some small degree. But is there any means of selecting those offspring which vary in the same manner, crossing them and keeping their offspring separate and thus producing selected races: otherwise as the wild animals freely cross, so must such small heterogeneous varieties be constantly counter-balanced and lost, and a uniformity of character kept up preserved. The former variation as the direct and necessary effects of causes, which we can see can act on them, as size of body from amount of food, effect of certain kinds of food on certain parts of bodies &c. &c.; such new varieties may then become adapted to those external natural agencies which act on them. But can varieties be produced adapted to end, which cannot possibly influence their structure and which it is absurd to look at as effects of chance. Can varieties like some vars of domesticated animals, like almost all wild species be produced adapted by exquisite means to prey on one animal or to escape from another—or rather, as it puts out of question effects of intelligence and habits, can a plant become adapted to animals, as a plant which cannot be impregnated without agency of insect; or hooked seeds depending on animal’s existence: woolly animals cannot have any direct effect on seeds of plant. This point which all theories about climate adapting woodpecker to crawl up trees, «illegible» mistletoe, «sentence incomplete». But if every part of a plant or animal was to vary «illegible», and if a being infinitely more sagacious than man (not an omniscient creator) during thousands and thousands of years were to select all the variations which tended towards certain ends (or were to produce causes which tended to the same end), for instance, if he foresaw a canine animal would be better off, owing to the country producing more hares, if he were longer legged and keener sight—greyhound produced. If he saw that aquatic animal would need skinned toes. If for some unknown cause he found it would advantage a plant, which like most plants is occasionally visited by bees &c.: if that plant’s seed were occasionally eaten by birds and were then carried on to rotten trees, he might select trees with fruit more agreeable to such birds as perched, to ensure their being carried to trees; if he perceived those birds more often dropped the seeds, he might well have selected a bird who would «illegible» rotten trees or gradually select plants which he had proved to live on less and less rotten trees. Who, seeing how plants vary in garden, what blind foolish man has done in a few years, will deny an all-seeing being in thousands of years could effect (if the Creator chose to do so), either by his own direct foresight or by intermediate means—which will represent the creator of this universe. Seems usual means. Be it remembered I have nothing to say about life and mind and all forms descending from one common type. I speak of the variation of the existing great divisions of the organized kingdom, how far I would go, hereafter to be seen.

Before considering whether there be any natural means of selection, and secondly (which forms the 2nd Part of this sketch) the far more important point whether the characters and relations of animated things are such as favor the idea of wild species being races descended from a common stock, as the varieties of potato or dahlia or cattle having so descended, let us consider probable character of selected races wild varieties.

Natural Selection. De Candolle’s war of nature—seeing contented face of nature—may be well at first doubted; we see it on borders of perpetual cold. But considering the enormous geometrical power of increase in every organism and as every country, in ordinary cases countries must be stocked to full extent, reflection will show that this is the case. Malthus on man—in animals no moral check restraint—they breed in time of year when provision most abundant, or season most favorable, every country has its seasons—calculate robins—oscillating from years of destruction. If proof were wanted let any singular change of climate occur here, how astoundingly some tribes increase, also introduced animals, the pressure is always ready—capacity of alpine plants to endure other climates—think of endless seeds scattered abroad—forests regaining their percentage—a thousand wedges are being forced into the economy of nature. This requires much reflection; study Malthus and calculate rates of increase and remember the resistance—only periodical.

The unavoidable effect of this is that many of every species are destroyed either in egg or young or mature (the former state the more common). In the course of a thousand generations infinitesimally small differences must inevitably tell; when unusually cold winter, or hot or dry summer comes, then out of the whole body of individuals of any species, if there be the smallest differences in their structure, habits, instincts senses, health &c., it will on an average tell; as conditions change a rather larger proportion will be preserved: so if the chief check to increase falls on seeds or eggs, so will, in the course of 1000 generations or ten thousand, those seeds (like one with down to fly) which fly furthest and get scattered most ultimately rear most plants, and such small differences tend to be hereditary like shades of expression in human countenance. So if one parent fish deposits its egg in infinitesimally different circumstances, as in rather shallower or deeper water &c., it will then tell.

Let hares increase very slowly from change of climate affecting peculiar plants, and some other «illegible» rabbit decrease in same proportion let this unsettle organization of, a canine animal, who formerly derived its chief sustenance by springing on rabbits or running them by scent, must decrease too and might thus readily become exterminated. But if its form varied very slightly, the long legged fleet ones, during a thousand years being selected, and the less fleet rigidly destroyed must, if no law of nature be opposed to it, alter forms.

Remember how soon Bakewell on the same principle altered cattle and Western, sheep—carefully avoiding a cross (pigeons) with any breed. We cannot suppose that one plant tends to vary in fruit and another in flower, and another in flower and foliage—some have been selected for both fruit and flower: that one animal varies in its covering and another not—another in its milk. Take any organism and ask what is it useful for and on that point it will be found to vary—cabbages in their leaf—corn in size and quality of grain, both in times of year—kidney beans for young pod and cotton for envelope of seeds &c. &c.: dogs in intellect, courage, fleetness and smell: pigeons in peculiarities approaching to monsters. This requires consideration—should be introduced in first chapter if it holds, I believe it does. It is hypothetical at best.

Nature’s variation far less, but such selection far more rigid and scrutinizing. Man’s races not even so well only not better adapted to conditions than other races, but often not one race adapted to its conditions, as man keeps and propagates some alpine plants in garden. Nature lets an animal live, till on actual proof it is found less able to do the required work to serve the desired end, man judges solely by his eye, and knows not whether nerves, muscles, arteries, are developed in proportion to the change of external form.