{226} <Note in original.> The selection, in cases where adult lives only few hours as Ephemera, must fall on larva--curious speculation of the effect <which> changes in it would bring in parent. _Natural means of Selection{227}._ {227} This section forms part of the joint paper by Darwin and Wallace read before the Linnean Society on July 1, 1858. De Candolle, in an eloquent passage, has declared that all nature is at war, one organism with another, or with external nature. Seeing the contented face of nature, this may at first be well doubted; but reflection will inevitably prove it is too true. The war, however, is not constant, but only recurrent in a slight degree at short periods and more severely at occasional more distant periods; and hence its effects are easily overlooked. It is the doctrine of Malthus applied in most cases with ten-fold force. As in every climate there are seasons for each of its inhabitants of greater and less abundance, so all annually breed; and the moral restraint, which in some small degree checks the increase of mankind, is entirely lost. Even slow-breeding mankind has doubled in 25 years{228}, and if he could increase his food with greater ease, he would double in less time. But for animals, without artificial means, _on an average_ the amount of food for each species must be constant; whereas the increase of all organisms tends to be geometrical, and in a vast majority of cases at an enormous ratio. Suppose in a certain spot there are eight pairs of [robins] birds, and that _only_ four pairs of them annually (including double hatches) rear only four young; and that these go on rearing their young at the same rate: then at the end of seven years (a short life, excluding violent deaths, for any birds) there will be 2048 robins, instead of the original sixteen; as this increase is quite impossible, so we must conclude either that robins do not rear nearly half their young or that the average life of a robin when reared is from accident not nearly seven years. Both checks probably concur. The same kind of calculation applied to all vegetables and animals produces results either more or less striking, but in scarcely a single instance less striking than in man{229}. {228} Occurs in _Origin_, Ed. i. p. 64, vi. p. 79. {229} Corresponds approximately with _Origin_, Ed. i. pp. 64-65, vi. p. 80.