136 Mr. George J. Romanes [Feb. 8, 



the wild and of the domestic duck. For, according to Dr. Rae, " If 

 the eggs of a wild duck are placed with those of a tame duck under a 

 hen to be hatched, the ducklings from the former, on the very day 

 they leave the egg, will immediately endeavour to hide them- 

 selves, or take to the water, if there be any water, should anyone 

 approach, whilst the young from the tame duck's eggs will show 

 little or no alarm." Now, as neither rabbits nor ducks are likely to 

 have been selected by man to breed from on account of tameness, we 

 may set down the loss of wildness in the domestic breeds to the un- 

 compounded effects of hereditary memory of man as a harmless 

 animal, just as we attributed the original acquisition of instinctive 

 wildness to the hereditary memory of man as a dangerous animal; in 

 neither case can we suppose that the principle of selection has operated 

 in any considerable degree. 



Thus far, for the sake of clearness, I have dealt separately with 

 these two factors in the formation of instinct — natural selection and 

 lapsing intelligence — and have sought to show that either of them 

 working singly is sufficient to develop some instincts. But, no 

 doubt, in the case of most instincts intelligence and natural selection 

 have gone hand in hand, or co-operated, in producing the observed 

 results — natural selection always securing and rendering permanent 

 any advances which intelligence may have made. Thus, to take one 

 case as an illustration. Dr. Kae tells me that the grouse of North 

 America have the curious instinct of burrowing a tunnel just below 

 the surface of the snow. In the end of this tunnel they sleep 

 securely, for when any four-footed enemy approaches the mouth of 

 the tunnel, the bird, in order to escape, has only to fly up through 

 the thin covering of snow. Now in this case the grouse probably 

 began to burrow in the snow for the sake of warmth, or concealment, 

 or both ; and, if so, thus far the burrowing was an act of intelligence. 

 But the longer the tunnel the better would it serve in the above- 

 described means of escape ; therefore natural selection would tend to 

 preserve the birds which made the longest tunnels, until the utmost 

 benefit that length of tunnel could give had been attained. 



And similarly, I believe, all the host of animal instincts may be 

 fully explained by the joint operation of these two causes — intelli- 

 gent adjustment and survival of the fittest. For now, I may draw 

 attention to another fact which is of great importance, viz. that 

 instincts admit of being modified as modifying circumstances may 

 require. In other words, instincts are not rigidly fixed, but are 

 plastic, and their plasticity renders them capable of improvement or 

 of alteration, according as intelligent observation requiies. The 

 assistance which is thus rendered by intelligence to natural selection 

 must obviously be very great, for under any change in the surround- 

 ing conditions of life which calls for a corresponding change in the 

 ancestral instincts of the animal, natural selection is not left to wait, 

 as it were, for the required variations to arise fortuitously ; but is from 

 the first furnished by the intelligence of the animal with the particular 

 variations which are needed. 



