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Cambridge University Library: Darwin Manuscripts Catalogue DAR 208: 39d
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Notebook D: 101,102, 133-136 (excised pages)
D 134e
1838.09.23-1838.09.25 & 1838.09.25 & 1838.09.28
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Editorial Symbols: ‹ › = deleted text   « » = interlined text   BOLD = text added


do. p. 461.— Lower Silurian— several existing genera. Nautilus turbo. buccinum. turritella. terebratula, orbiculas, with many extinct forms & Trilobites1
Sept 25th. In considering infertility of hybrids inter se, the first cross generally brothers & sisters, & therefore somewhat unfavourable—2
28th. «I do not doubt, every one till he thinks deeply has assumed that increase of animals exactly proportiona[l]a to the number that can live.—» We ought to be far from wondering of changes in number of species, from small changes in nature of locality.3 Even the energetic language of ‹Malthus› «Decandoelle4» does not convey the warring of the species as inference from Malthus.— «increase of brutes, must be prevented solely by positive checks, excepting that famine may stop desire.—5» in Nature production does not increase, whilst no checks prevail, but the positive check of famine & consequently death..6



page crossed pencil
aproportiona[l] ] part of 'l' on stub.
Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin
Transcription and apparatus © American Museum of Natural History
  • 1. Lyell 1838a:461, 'There are also several genera of mollusca in this deposit, and it is an interesting fact, that with many extinct forms of testacea peculiar to the lower Silurian rocks, such as orthoceras, pentamerus, spirifer, and productus, others are associated belonging to genera still existing, as nautilus, turbo, buccinum, turritella, and orbicula.' Passage scored.
  • 2. Thus hybrids would suffer from the combined disadvantages of inbreeding and hybridization. Compare with D10 and D14.
  • 3. See note D133−1.
  • 4. See Lyell 1837, 3:87−88, ' “ All the plants of a given country,” says De Candolle, in his usual spirited style, “ are at war one with another” .'
  • 5. See note D134−6. See also Darwin's previous interest in inbreeding stopping desire, e.g. B176, D177.
  • 6. Malthus 1826, 1:12−13, 'These checks to population, which are constantly operating with more or less force in every society, and keep down the number to the level of the means of subsistence, may be classed under two general heads— the preventive, and the positive checks.
      'The preventive check, as far as it is voluntary, is peculiar to man, and arises from that distinctive superiority in his reasoning faculties, which enables him to calculate distant consequences. The checks to the indefinite increase of plants and irrational animals are all either positive, or, if preventive, involuntary.'