Closer inquiry verifies the conclusion to which these facts point. The microscope shows that along with the increase of bulk common in advanced life, there goes on what is called “fatty degeneration:” oil-globules are deposited where there should be particles of flesh—or rather, we may say, the hydrocarbonaceous molecules locally produced by decomposition of the nitrogenous molecules, have not been replaced by other nitrogenous molecules, as they should have been. This fatty degeneration is, indeed, a kind of local death. For so regarding it we have not simply the reason that an active substance has its place occupied by an inert substance; but we have the further reason that the flesh of dead bodies, under certain conditions, is transformed into a fatty matter called adipocere.
The infertility that accompanies fatness in domestic animals has, however, other causes than that declining constitutional vigour which the fatness commonly indicates. Being artificially fed, these animals cannot always obtain what their systems need. That which is given to them is given expressly because of its fattening quality. And since the capacity of the digestive apparatus remains the same, the absorption of fat-producing materials in excess, implies defect in the absorption of materials from which the tissues are formed, and out of which young ones are built up. Moreover, this special feeding with a view to rapid and early fattening, continued as it is through generations, and accompanied as it is by a selection of individuals and varieties which fatten most readily, tends to establish a modified constitution, more fitted for producing fat and correspondingly-less fitted for producing flesh—a constitution which, from this relatively-deficient absorption of nitrogenous matters, is likely to become infertile; as, indeed, these varieties often do become. Hence, no conclusions respecting the effects of high nutrition, properly so-called, can be drawn from cases of this kind. The cases are, in truth, of a kind which could not exist but for human agency. Under natural conditions no animal would diet itself in the way required to produce such results. And if it did its race would quickly disappear.[62]
There is yet another mode in which accumulation of fat diminishes fertility. Even supposing it unaccompanied by a smaller absorption of nitrogenous materials, it is still a cause of lessening the surplus of nitrogenous materials. For the repair of the motor tissues becomes more costly. Fat stored-up is weight to be carried. A creature loaded with inert matter must, other things equal, consume a greater amount of tissue-forming substances for keeping its locomotive apparatus in order; and thus expending more for self-maintenance can expend less for race-maintenance. Abnormal plethora is thus antagonistic to reproduction in a double way. It ordinarily implies a smaller absorption of tissue-forming matters, and an increased demand on the diminished supply. Hence fertility decreases in a geometrical progression.
The counter-conclusion drawn from facts of this class is, then, due to a misconception of their nature—a misconception arising partly from the circumstance that the increase of bulk produced by fat is somewhat like the increase of bulk which growth of tissues causes, and partly from the circumstance that abundance of good food normally produces a certain quantity of fat, which, within narrow limits, is a valuable store of force-evolving material. When, however, we limit the phrase high nutrition to its proper meaning—an abundance of, and due proportion among, all the substances which the organism needs—we find that, other things equal, fertility always increases as nutrition increases. And we see that these apparently-exceptional cases, are cases which really show us the same thing; since they are cases of relative innutrition.
[Note.—By a strange oversight when writing this chapter in the first edition—an oversight I was on the eve of repeating in this present edition—I omitted to bring forward the familiar and all-important evidence furnished by the variations of genesis which ordinarily accompany the alternations of the seasons. These variations, in multitudinous creatures of all types, show unmistakably that reproduction begins at those times of the year when greater warmth and larger supplies of food render maintenance of individual life relatively easy, and when there is therefore a surplus available for producing new individuals. Conversely, along with the decrease of heat and the relative deficiency of food which make it comparatively difficult in winter to maintain individual life, there ceases to be the power of producing other lives: the reproductive organs become quiescent and often dwindle. With this general fact is associated a special fact. Though among wild animals—birds, mammals, and others—breeding ceases when Nature no longer supplies abundant food and warmth; in domesticated mammals and birds, artificially supplied with food and warmth, the breeding season is greatly extended and often made continuous, as, under the same conditions, it is in Man himself.
Evidence yielded by the vegetal world is less conspicuous, for the reason that the cold which arrests reproductive activity also arrests individual activity: growth of the individual and multiplication of the race vary simultaneously with variations in the seasons. Still there are some familiar facts showing that the external conditions which favour nutrition also bring about reproduction. Early in the year we are supplied with flowers from regions warmer than our own, and by and by there come to our markets fruits and vegetables from the south of France, the Channel Islands, and even from the Scilly Isles, which are much in advance of those furnished by the gardens of our own colder regions: reproduction commences earlier where the light and heat furthering nutrition are greater. And then there is a kindred meaning in the not unfrequent occurrence of a second flowering and even of a second fruiting in warm, bright and prolonged autumns. Here the abnormal re-commencement of reproduction is determined by an abnormal increase of nutrition.]
CHAPTER X.
SPECIALITIES OF THESE RELATIONS.
§ 356. Tests of the general doctrines set forth in preceding chapters, are afforded by organisms having modes of life which diverge widely from ordinary modes. Here, as elsewhere, aberrant cases yield crucial proofs.
If certain organisms are so circumstanced that highly-nutritive matter is supplied to them without stint, and they have nothing to do but absorb it, we may infer that their powers of propagation will be enormous.