Aristotle · a new plain-English translation from the original language
1| ON LENGTH AND SHORTNESS OF LIFE.
2| As for the fact that some animals are long-lived and others short-lived, and about the length and shortness of life in general, we must examine the causes. The necessary starting point of the inquiry is first to work through the puzzles about them. For it is not clear whether the cause is one and the same, or different, for all animals and plants having some long-lived and some short-lived; for among plants too, some have a life of a single year while others live for a long time. Further, it is a question whether the same things are long-lived and naturally healthy among things constituted by nature, or whether short-livedness and being disease-prone are separate, or whether, in the case of some diseases, bodies whose nature is disease-prone coincide with the short-lived, while in the case of others there is nothing to prevent disease-prone bodies from being long-lived. Now sleep and waking have been discussed earlier, and life and death must be discussed later, and likewise disease and health, so far as these fall within natural philosophy; but for now we must examine the cause of some animals being long-lived and others short-lived, as was said before. This difference belongs both to whole genera as against other whole genera, and to different members within one and the same species as against each other. I mean that man differs from horse by genus (for the human genus is longer-lived than that of horses), while man differs from man by species; for there are also humans who are long-lived and others short-lived, differing from each other by region: those among the peoples in hot regions are longer-lived, and those in cold regions shorter-lived. And among those who inhabit the same region, some likewise differ from one another in this same way.
3| We must grasp, then, what it is among things constituted by nature that is easily destroyed and what is not easily destroyed. For fire and water and the things akin to these, not having the same power, happen to be causes of coming-to-be and destruction for each other, so that it is reasonable that each of the other things too, being made of and composed from these, should share in their nature — that is, whatever is not a composite of many things, such as a house. Now concerning the other things there is a different account; for many existing things have their own particular kinds of destruction, as with knowledge, health, and disease. For these are destroyed even while the things capable of receiving them are not destroyed but preserved — for instance, the destruction of ignorance is recollection and learning, while the destruction of knowledge is forgetting and being deceived. But it is accidentally that the destructions of these other things follow upon natural things; for when animals are destroyed, the knowledge and the health that are in animals are destroyed along with them. Hence one might also draw a conclusion about the soul from these considerations: for if the soul is not present by nature but is in the body in the way knowledge is in the soul, then there would be some other destruction of it besides the destruction it undergoes when the body is destroyed. So since it does not appear to be of this kind, its relation to its partnership with the body would have to be otherwise.
4| Perhaps one might reasonably raise this puzzle: is there some place where the destructible will be indestructible, as fire is indestructible when above, where there is nothing contrary to it? For the things that belong to contraries are destroyed accidentally, by the destruction of those contraries — for contraries are eliminated by one another; but none of the contraries present in substances is destroyed accidentally, because substance is not predicated of any underlying subject. So that which has no contrary, and the place in which there is no contrary, would be incapable of being destroyed; for what will be the agent of destruction, if it is only by contraries that destruction occurs, and this is not present, either altogether or in that place? Or is this true in one sense and not in another? For it is impossible for a thing possessing matter not to have its contrary present in it in some way. For it is possible for the hot, or the straight, to be present throughout something entirely, but it is impossible for anything to be entirely hot or straight or white; for then the affections would exist separately. If, then, whenever the active and the passive are present together, the one always acts and the other is acted upon, it is impossible for there to be no change. Further, if it is necessary to produce residue, and the residue is a contrary — for change always proceeds from a contrary, and the residue is what is left over from what came before.
5| But if a thing entirely expels what is contrary to it in actuality, then in that place too it would be indestructible. Or not — rather, it is destroyed by what surrounds it. If this is sufficient, then the point is settled from what has been said; but if not, we must suppose that something actually contrary is present within, and that residue comes to be. That is why a smaller flame is burned up accidentally by a larger one: because the nourishment — that is, the smoke — which the smaller flame uses up over a long time, the larger flame uses up quickly. That is why everything is always in motion, and either comes to be or is destroyed. And what surrounds a thing either cooperates with it or works against it. And because of this, things that are relocated become longer-lived or shorter-lived than their nature would give them, but nowhere eternal, in the case of things that have contraries; for matter immediately carries its contrary within it. So that if the change is one of place, the thing changes locally; if of quantity, by growth and diminution; if of an affection, it is altered.
6| Now it is not the largest things that are less destructible (for the horse is shorter-lived than man), nor the small ones (for most insects live only a year), nor plants as a whole compared with animals (for some plants live only a year), nor the blooded (for the bee lives longer than some blooded creatures), nor the bloodless (for the soft-bodied creatures live only a year, yet are bloodless), nor those that live on land (for there are plants that live only a year, and land animals too), nor those that live in the sea — for there too the shelled creatures and the soft-bodied creatures are short-lived. In general, the longest-lived things are found among plants, such as the palm tree; then among blooded animals more than among bloodless ones, and among land animals more than among water-dwelling ones. So that when these traits are combined — being blooded and being land-dwelling — the result is the longest-lived of animals, such as man and the elephant. And indeed, for the most part, the larger are longer-lived than the smaller; for size, too, is found to belong to the other longest-lived things, just as to those mentioned.
7| One might examine the cause of all this as follows. For we must grasp that the animal is by nature moist and hot, and that living is of this character, while old age is cold and dry, and so is the dead body; for this is how it appears. Now the matter of bodies, for the things that exist, is these — the hot and the cold, the dry and the moist. It is necessary, then, that as a thing grows old it dries out. Hence the moisture in it must not be easily dried up. And this is why fatty things do not putrefy. The cause is that they are of air; and air, relative to the other elements, is fire, and fire does not become rotten. Nor again must the moisture be small in quantity; for what is small is also easily dried up. And this is why, generally speaking, large animals and plants are longer-lived, as was said before; for it is reasonable that the larger should have more moisture. But it is not only for this reason that they are longer-lived; for there are two causes, the quantity and the quality, so that there must not only be an abundance of moisture, but this moisture must also be hot, so that it is neither easily congealed nor easily dried up. And this is why man is longer-lived than some larger creatures; for those that fall short in quantity of moisture are longer-lived, provided they exceed by a greater ratio in quality than they fall short in quantity.
8| In some animals the hot element is the fatty kind, which at once makes the animal resistant to drying and resistant to chilling; in others the hot element carries a different humor. Further, what is going to be long-lived must not be prone to residue. For such a thing destroys the animal, either by disease or by nature; and the power of the residue is opposed to it, and destructive — in one case destructive of the whole nature, in another of a part. Hence animals given to mating and productive of much seed age quickly; for seed is a residue, and moreover it dries the animal as it departs. And for this reason the mule is longer-lived than the horse and the donkey from which it was born, and females are longer-lived than males, if the males are given to mating; hence male sparrows are shorter-lived than females. Further, whatever males undergo hard toil age more because of the toil; for toil dries, and old age is dry. By nature, and to speak generally, males are longer-lived than females; the cause is that the male is a hotter animal than the female. The same animals are longer-lived in warm regions than in cold regions, for the same cause through which they become larger. And this effect on size is most evident in animals that are cold by nature;
9| hence snakes and lizards and scaly creatures grow large in hot regions, and in the Red Sea the shelled creatures grow large; for hot moisture is the cause both of growth and of life. But in cold regions the moisture in animals is more watery; hence it freezes easily, so that some bloodless or low-blooded animals do not occur at all in the regions toward the north — neither the land ones on earth nor the water ones in the sea — while others do occur, but are smaller and shorter-lived; for the frost takes away growth. Both plants and animals that take in no nourishment perish; for they consume themselves. For just as a great flame burns up and destroys a small one by using up its fuel, so the natural heat, which is the primary agent of concoction, uses up the matter in which it resides. Water animals are less long-lived than land animals not because they are simply moist, but because they are watery; and moisture of this kind is easily destroyed, because it is cold and freezes easily. And the bloodless animal is short-lived for the same reason, unless it defends itself by size; for it has neither fat nor sweetness.
10| For in an animal the fatty is the sweet; hence bees are longer-lived than other, larger animals. Among plants are found the longest-lived things, and more so than among animals — first because they are less watery, so that they do not freeze easily; then, they have oiliness and viscosity, and though dry and earthy, they nonetheless have moisture that is not easily dried out. As to why the nature of trees is long-lasting, we must grasp the cause; for it has a cause peculiar to itself compared with animals, except compared with insects. For plants are always becoming new; hence they are long-lasting. For the shoots are always different ones, while the old ones age. And likewise the roots. But not at the same time: rather, at one time only the trunk and branches perish, while others grow up alongside them; and when this happens, new roots come to be out of what already exists, and thus it continues always, part perishing and part coming to be; hence plants are also long-lived. Plants resemble insects, as was said before; for when divided they live on, and two or many come to be from one. But insects, though they reach the point of living when divided, cannot do so for long; for they do not have the organs, nor can the principle present in each part produce them. But the principle in the plant can produce them;
11| for everywhere it has, potentially, both root and stem. Hence from this principle there is always proceeding, on the one hand the new, on the other the aging, differing only slightly in being long-lived, in the same way as cuttings that are planted out. For indeed, in the case of taking cuttings, one might say that this same thing happens in a way; for what is planted out as a cutting is a part of the parent. In the case of cuttings, then, this happens through separation, but in the other case through continuity. The cause is that the principle is present everywhere, inhering potentially. And the same thing occurs in the case of both animals and plants. For among animals the males are, for the most part, longer-lived; and of these, the upper parts are larger than the lower (for the male is more stunted than the female in the lower part), and heat is in the upper part, and cold in the lower; and among plants, those that are top-heavy are longer-lived. Such are those that are not annual but tree-like; for the upper part of the plant, and its head, is the root, while annual plants direct their growth toward the lower part and toward the fruit. But on this point, considered in its own right, a determination will be made in the works on plants; for now, the cause has been stated concerning the other animals, regarding both length of life and shortness of life.
12| It remains for us to examine youth and old age, and life and death; for once these have been determined, the inquiry concerning animals would reach its completion.