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HARDWICKE'S SCIENCE-GOSSIP. 



DARWIN'S OPINIONS ON INSTINCT. 



A POSTHUMOUS essay on " Instinct," by the 

 late Charles Darwin, was read on December 

 6th, at the Linnean Society, before a very large and 

 distinguished audience of Fellows. The paper, which 

 treated of the instincts of animals, and the bearing of 

 the subject on the theory of natural selection, was 

 originally written for the "Origin of Species," but 

 never published. It discussed the migration of birds 

 and mammals, and after narrating a great series of 

 curious facts, concluded with the inference that 

 though there were many aspects of the question 

 which admitted of no immediate explanation, the 

 migratory instinct was inherited from ancestors who 

 had to compass (for the sake of food or other causes) 

 long distances, when the conditions of land and water 

 were different from what they are at present. He 

 then considered liow the more remarkable migrations 

 could possibly have originated. Take the case of a 

 bird being driven each year, by cold or want of food, 

 slowly to travel nortliward, as is the case with some 

 birds ; and in time we may well believe that this com- 

 pulsory travelling would become instinctive, as with 

 the sheep in Spain. Now, during the long course of 

 ages, let valleys become converted into estuaries, and 

 then into wider and wider arms of the sea ; and still 

 he could well believe that the impulse which leads 

 the pinioned goose to scramble northward would lead 

 our bird over the trackless waters ; and that, by the 

 aid of the unknown power by which many animals 

 (and savage men) can retain a true course, it would 

 safely cross the sea now covering the submerged path 

 of its ancient land journey. Animals on oceanic 

 islands, and other localities where they have never met 

 with man or beasts of prey, are devoid of fear. This 

 instinctive dread they subsequently acquire, for their 

 own preservation, and transmit it to their descendants. 

 At the Galapagos Islands Mr. Darwin pushed a hawk 

 off a tree with the muzzle of his gun, and the little 

 bird drank water out of a vessel which he held in his 

 hand. But this tameness is not general, but special 

 towards man ; for at the Falklands the geese build 

 on the outlying islands on account of the foxes. These 

 wolf-like foxes were here as fearless of man as were 

 the birds, and the sailors in Byron's voyage, mistaking 

 their curiosity for fierceness, ran into the water to 

 avoid them. In all old civilised countries the wari- 

 ness and fear of even young foxes and wolves are well 

 known. At the Galapagos Islands the great land 

 lizards (Amblyrhynchus) were extremely tame, so that 

 Mr. Darwin could pull them by the tail ; whereas in 

 other parts of the world large lizards are wary enough. 

 The aquatic lizard of the same genus lives on the 

 coast, is adapted to swim and dive perfectly, and 

 , feeds on submerged algae; no doubt it must be ex- 

 posed to danger from the sharks, and consequently, 

 though quite tame on the land, he could not drive 

 them into the water ; and when he threw them in 



they always swam directly back to the shore. Animals' 

 feigning death seemed to Mr. Darwin a remarkable 

 instinct, but he considered that there was much 

 exaggeration on the subject. It struck him as a 

 strange coincidence that the insects should have come 

 to exactly simulate the state which they took when 

 dead. Hence he carefully noted the simulated posi- 

 tions of seventeen kinds of insects (including an lulus, 

 spider, and Oniscus) belonging to the most distinct 

 genera, both poor and first-rate shammers ; afterwards 

 he procured naturally dead specimens of some of these 

 insects, others he killed with camphor by an easy slow 

 death. The result was that in no one instance was the 

 attitude exactly the same, and in several instances the 

 attitude of the feigners and of the really dead were as 

 unlike as they possibly could be. Bird-nesting and the 

 habitations of other animals were next discussed, the 

 general conclusion being that though there are various 

 adaptations of inherited instincts to suit varying cir- 

 cumstances, yet that these variations all tend to pre- 

 serve the species in the struggle for existence, by 

 conducing to the " survival of the fittest." Although 

 he did not doubt that intelligence and experience 

 often come into play in the nidification of birds, yet 

 both often fail ; a jackdaw has been seen trying in 

 vain to get a stick through a turret window, and had 

 not sense to draw it in lengthways ; Gilbert "White 

 describes some martins which year after year built 

 their nests on an exposed wall, and year after year 

 they were washed down. The Fiirnariiis cu)iicidarius 

 in S. America makes a deep burrow in mud-banks for 

 its nest ; and he saw these little birds vainly burrow- 

 ing numerous holes through mud-walls, over which 

 they were constantly ilitting, without thus perceiving 

 that the walls were not nearly thick enough for their 

 nests. After an exhaustive account of various traits 

 of instinct, and difficulties in the way of his theory, 

 explaining all of them, the paper closed with the 

 following general conclusion:- — "We have chiefly 

 considered the instinct 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 whetlier, 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 dis- 

 positions in our domesticated animals, and their 

 parallelism (subject to having less time) 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 



