OCR Text |
Show 206 DIFFICULTIES ON THEORY. CHAP. VI. the larger country t h ere WI'l l h ave existed more i.n.d i-viduals, and more diversified forms, and the competition will have been severer, and thus the standard of per~ect. ion will have been rendered higher. N atu~al selectiOn will not necessarily produce absolute per~ection ; nor, as far as we can judge by our limited faculties, can absolute perfection be everywhere found. On the theory of natural selection we ca?- clearly understand the full meaning of that old canon In natural history " Natura non facit saltum." This canon, if we look only to the present inhabitants of the world, is not strictly correct, but if we include all those of past times, it must by my theory be strictly true. It is generally acknowledged that all organic beings have been formed on two great laws-Unity of Type, and the Conditions of Existence. By unity of type is meant that fundamental agreement in structure, which we see in organic beings of the same class, and which is quite independent of their habits of life. On my theory, unity of type is explained by unity of descent. The expression of conditions of existence, so often insisted ~n by the illustrious Cuvier, is fully embraced by the pnnciple of natural selection. For natural selection acts by either now adapting the varying parts of each being to its organic and inorganic conditions of life; or by having adapted them during long-past periods of time: the adaptations being aided in some cases by use and disuse, being slightly affected by the direct action of the external conditions of life, and being in all cases subjected to the several laws of growth. Hence, in fact, the law of the Conditions of Existence is the higher law; as it includes, through the inheritance of former adaptations, that of Unity of Type. CHA.P. VII. INSTINCT. 207 CHAPTER VII. INSTINCT. Instincts comparable with habits, but different in their originInstincts graduated- Aphides and ants- Instincts variableDomestic instincts, their origin-Natural instincts of the cuckoo, ostrich, and parasitic bees- Slave-making ants- Hive-bee, its cell-making instinct-Difficulties on the theory of the Natural Selection of instincts-Neuter or sterile insects-Summary. THE subject of instinct might have been worked into the previous chapters ; but I have thought that it would be more convenient to treat the subject separately, especially as so wonderful an instinct as that of the hivebee making its cells will probably have occurred to many readers, as a difficulty sufficient to overthrow my whole theory. I must premise, that I have nothing to do with the origin of the primary mental powers, any .more than I have with that of life itself. We are concerned only with the diversities of instinct and of the other mental qualities of animals within the same class. I will not attempt any definition of instinct. It would be easy to show that several distinct mental actions are commonly embraced by this term; but every one understands what is meant, when it is said that instinct impels the cuckoo to migrate and to lay her eggs in other birds' nests.. An action, which we ourselves should require exper:ence to enable us to perform, when performed by an animal,. more especially by a very young one, without any e~perience, and when performed by many individuals In. t~e same way, without their knowing for what purpose It IS performed, is usually said to be instinctive. |