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Show 20 1'HE PRINCIPLE O.b; 0HA1'. l. T o th ose Who admit the gradual evolu.t ion o·f species, 1 h' 1 a most striking instance of the perfection Wit 1 w IC l the most difficult consensual moven1e~ts can ~e trans- m1' tte d, I·S afforded by the humming-bu·d Sph•i nx-moth (Macroglossa); for this moth, shortly after Its em~rgence from the cocoon, as shown by the ?loom _on Its unruffled scales, may be seen poised stationary 1n ~ho air, with its long hair-like proboscis uncurled and Inserted into the minute orifices of flowers; and no one, I believe has ever seen this moth learning to perform ' . . its difficult task which requires such unernng a1n1. When there 'exists an inherited or instinctive tendency to the performance of an action, or an in~ herited taste for certain kinds of food, some degree of habit in the individual is often or generally requisit.e. We find this in the paces of the horse, and to a certam extent in the pointing of dogs ; although some young dogs point excellently the first time they a~·e ta!{en out, yet they often associate the pr?per I~hentecl attitude with a wrong odour, and even with eyes1ght. I have heard it asserted that if a calf be allowed to suck its mother only once, it is much more diffi. cult afterwards to rear it by hand.3 Caterpillars which have been fed on the leaves of one kind of tree have been known to perish from hunger rather tha~ to eat the leaves of another tree, although this afforded them their proper food, under a state of nature ; 4 and so it is in many other cases. 3 A remark to much the same effect was made long ngo by Hippo· crates and by the illustrious Harvey; for both assert that a young animal forgets in the course of a few days the art of sucking, _and cannot without some difficulty again acquire it. I give these assorilOJJS on the authority of Dr. Darwin, ' Zoonomia,' 1794, vol. i. p. 140. , , , 1 ) 4 Seo for my authorities, and for various analogous facts, 1 !~ Variation of Animals and Plants under Domestication,' 1868, vol. 11' ll· 304. CHAP. r. SERVICEAl3t~ ASSOCIA1,ED HABITS. 31 The power of Association is admitted by everyone. 1\ir. Bain remarks, that "actions, sensations, and states " of feeling, occurring together or in close succession, '" tend to grow together, or cohere, in such a way that " when any one of the1n is afterwards presented to the '' mind, the others are apt to be brought up in idea." 5 It is so important for our purpose fully to recognise that actions readily become associated with other actions and with various states of the mind, that I will give a good many instances, in the first place relating to man, and aftenvards to the lower animals. Son1e of the instances are of a very trifling nature, but they are as good for our purpose as more important habits. It is known to everyone how difficult, or even impossible it is, without repeated trials, to move the nmbs in certain opposed directions which have never been practised. Analogous cases occur with sensations, as in the common experiment of rolling a marble beneath the tips of two crossed fingers, when it feels exactly like two marbles. Everyone protects himself when falling to the ground by extending his arms, and as Professor Alison has remarked, few can resist acting thus, when voluntarily falling on a soft bed. A man when going out of doors puts on his gloves .quite unconsciously; and this may seem an extremely simple operation, but he who has taught a child to put on gloves, knows that this is by no means the case. When our minds are much affected, so are the movement@ of our bodies; but here another principle be- 5 ' The Senses and tho Intellect,' 2nd edit. 1864, p. 332. Prof. Huxley remarks (' Elementary Lessons in Physiology,' 5th edit. 1872, p. 306), ''It may be luicl down as a rul , that, if any two montal s~a~e;.; '' be called up too-ether or in succession, with due fi·equcncy and VlYidtt ness, the subse~uent ~roduction of tho one of them will suilico to call ''up tho other, and that whether we dcf:liro it or not." |
