RECORD: Ponderer. 1869. Darwin's elephants. Athenaeum no. 2171 (5 June): 72.
REVISION HISTORY: Transcribed by John van Wyhe 2008. RN1
Darwins Elephants.—In the last edition of Mr. Darwin's 'Origin of Species,' he makes the following statement (chap, iii., page 74, line 18):— "The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum state of natural increase. It will be under the mark to assume that it begins breeding when thirty years old, and goes on breeding till ninety years old, bringing forth three pair of young in this interval. If this be so, at the end of the fifth century there would be alive fifteen million elephants descended from the first pair." Perhaps some of your readers will be able to enlighten my dull intellect as to the process of reasoning by which this result is obtained. According to Mr. Darwin's theory, each pair brings forth a pair when it is thirty, when it is sixty, and when it is ninety. Hence if there be one pair in the first year, there will be one pair born in the thirtieth year; these two pairs will produce two pairs in the sixtieth year, and these four will produce four pairs in the ninetieth. After that we have only to add the numbers born in the three preceding periods to find out how many are born in each period; because after they have attained the age of ninety years they cease to breed. This method of reasoning gives the number of pairs born in each period of thirty years as 1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1,705,3,136,5,768,10,609, 19,513; the last number being born in the period commencing with the five hundred and tenth year. Therefore the number of elephants alive at that time would be 42,762 pairs, that is, 85,524 elephants, less the number that would have died by reason of their age. But Mr. Darwin says that there would be fifteen millions. On what does he base his calculation?
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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)
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