188 MENTAL EVOLUTION IN ANIMALS. 



We see, then, that non-intelligent habits of non-adaptive 

 or useless character may be strongly inherited by domestic 

 animals. As showing that the same is true of breeds or strains 

 in wholly wild animals, I may quote Humboldt, who says,* 

 that the Indians who catch monkeys to sell them " knew very 

 well that they can easily succeed in taming those which 

 inhabit certain islands ; while monkeys of the same species, 

 caught in the neighbouring continent, die of terror or rage 

 when they find themselves in the power of man :" and in his 

 MSS I find that Mr. Darwin has a note saying, " divers 

 dispositions seem to run in families of crocodiles." But one 

 of the most curious instances that I have met with of the 

 commencement of a racial and useless deviation from a 

 strong ancestral instinct, is one which is communicated to 

 Mr. Darwin in a letter from Mr. Thwaits, who writes from 

 Ceylon under the date 1860, and whose letter I find among 

 Mr. Darwin's MSS. Mr. Thwaits here says that his 

 domestic ducks quite lost their natural instincts with regard 

 to water, which ihey never enter unless driven. The young 

 birds, when forcibly placed in a tub of water are " quite 

 alarmed," and have to be quickly taken out again " or they 

 would drown in their struggling." Mr. Thwaits adds that 

 this peculiarity does not extend to all the ducks in the 

 island, but only occurs in one particular breed or strain. 



In Mr. Darwin's MSS I also find the following remarks : 

 " So many independent authors have stated that horses in 

 different parts of the world inherit artificial paces, that I 

 think the fact cannot be doubted. Dureau de la Malle 

 asserts that these different paces have been acquired since 

 the time of the Roman classics, and that from his own 

 observation they are inherited. f .... Tumbler pigeons 

 offer an excellent instance of an instinctive action, acquired 

 under domestication, which could not have been taught, but 

 must have appeared naturally, though probably afterwards 

 vastly improved by the continued selection of those birds 

 which showed the strongest propensity — more especially in 



* Personal Narrative, vol. iii, p. 383. 



t After giving numerous references on this point in a footnote, 

 Mr. Darwin concludes the latter thus : — " I may add that I was formerly 

 struck by no horse on the grassy plains of La Plata bavins; the natural bigb 

 action of some English borses." For a number of other instances of here- 

 ditary transmission of qualities in the case of the Horse, see Variation of 

 Animals and Plants. &c. vol. i, pp. 454-6. 



