{55} This may possibly refer to the amount of destruction going on. See _Origin_, Ed. i. p. 68, vi. p. 84, where there is an estimate of a later date as to death-rate of birds in winter. "Calculate robins" probably refers to a calculation of the rate of increase of birds under favourable conditions. {56} In the _Origin_, Ed. i. pp. 64, 65, vi. p. 80, he instances cattle and horses and certain plants in S. America and American species of plants in India, and further on, as unexpected effects of changed conditions, the enclosure of a heath, and the relation between the fertilisation of clover and the presence of cats (_Origin_, Ed. i. p. 74, vi. p. 91). {57} _Origin_, Ed. i. p. 74, vi. p. 91. "It has been observed that the trees now growing on ... ancient Indian mounds ... display the same beautiful diversity and proportion of kinds as in the surrounding virgin forests." {58} The simile of the wedge occurs in the _Origin_, Ed. i. p. 67; it is deleted in Darwin's copy of the first edition: it does not occur in Ed. vi. 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{59}; 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{60}) 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. {59} In a rough summary at the close of the Essay, occur the words:--"Every creature lives by a struggle, smallest grain in balance must tell." {60} Cf. _Origin_, Ed. i. p. 77, vi. p. 94. Let hares{61} increase very slowly from change of climate affecting peculiar plants, and some other <illegible> rabbit decrease in same proportion [let this unsettle organisation 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. {61} This is a repetition of what is given at p. 6.