SCIENTIFIC SOCIETIES. 35 



exhibit them ; (4) instincts performed only once during the lifetime of 

 an animal; (5) instincts of a trifling or useless character; (6) special 

 difficulties connected with the instinct of migration ; (7) sundry other 

 instincts presenting more or less difficulty to the theory of natural selection. 

 Mr. Darwin concludes : — " We have in this chapter chiefly considered the 

 instincts of animals under the point of view whether it is possible that they 

 could have been acquired through the means indicated on our theory, or 

 whether, even if the simpler ones could have been thus acquired, others 

 are so complex and wonderful that they must have been specially endowed, 

 and thus overthrow the theory. Bearing in mind the facts given on the 

 acquirement, through the selection of self-originating tricks or modification 

 of instinct, or through training and habit, aided in some slight degree 

 by imitation, of hereditary actions and dispositions in our domesticated 

 animals ; and their parallelism (subject to having less timej to the instincts 

 of animals in a state of nature ; bearing in mind that in a state of nature 

 instincts do certainly vary in some slight degree : bearing in mind how very 

 generally we find in allied but distinct animals a gradation in the more 

 complex instincts which show that it is at least possible that a complex 

 instinct might have been acquired by successive steps ; and which moreover 

 generally indicate, according to our theory, the actual steps by which the 

 instinct has been acquired, inasmuch as we suppose allied instincts to have 

 branched off at different stages of descent from a common ancestor, and 

 therefore to have retained, more or less unaltered, the instincts of the 

 several lineal ancestral forms of any one species ; bearing all this in mind, 

 together with the certainty that instincts are as important to an animal as 

 their generally correlated structures, and that in the struggle for life under 

 changing conditions, slight modifications of instinct could hardly fail 

 occasionally to be profitable to individuals, I can see no overwhelming 

 difficulty on our theory. Even in the most marvellous instinct known, 

 that of the cells of the hive-bee, we have seen how a simple instinctive 

 action may lead to results which fill the mind with astonishment. Moreover 

 it seems to me that the very general fact of the gradation of complexity of 

 instincts within the limits of the same group of animals ; and likewise the 

 fact of two allied species, placed in two distant parts of the world and 

 surrounded by wholly different conditions of life, still having very much in 

 common in their instincts, supports our theory of descent, for they are 

 explained by it ; whereas if we look at each instinct as specially endowed, 

 we can only say that it is so. The imperfections and mistakes of instinct 

 on our theory cease to be surprising ; indeed it would be wonderful that 

 far more numerous and flagrant cases could not be detected, if it were not 

 that a species which has failed to become modified and so far perfected in 

 its instincts that it could continue struggling with the co-inhabitants of the 

 same region, would simply add one more to the myriads which have become 



