108 SUMMARY. Cuap. VI. 



inatcriKil love or maternal hatred, though the latter fortunately 

 is most rare, is all the same to the inexr)rablc principle of natu- 

 ral selection. If we admire the several ini^enious contrivances, 

 by which orchids and many other plants are fertilized through 

 insect agency, can we consider as equally perfect the elabora- 

 tion of dense clouds of pollen by our fir-trees, so that a few 

 granules may be wafted by a chance breeze on to the ovules ? 



Summary : tJie Law of Unity of Type and oftJie Conditions 

 of Existence embraced by the Theory of JVcitural Se- 

 lection. 



We have in this chapter discussed some of the difficulties 

 and objections which may be urged against the theory. Many 

 of them are serious ; but I think that in the discussion light has 

 been thrown on several facts, which on the belief of indepen- 

 dent acts of creation are uttercly obscure. We have seen that 

 species at any one period are not indefinitely variable, and are 

 not linked together by a multitude of intermediate gradations, 

 partly because the process of natural selection will always be 

 very slow, and will act, at any one time, only on a few forms ; 

 and partly because the very process of natural selection implies 

 the continual supplanting and extinction of preceding and in- 

 termediate gradations. Closely-allied species, now living on a 

 continuous area, must often have been formed when the area 

 was not continuous, and when the conditions of life did not in- 

 sensibly graduate away from one part to another. When two 

 varieties are formed in two districts of a continuous area, an 

 intermediate variety will often be formed, fitted for an interme- 

 diate zone ; but, from reasons assigned, the intermediate variety 

 will usually exist in lesser numbers than the two forms which it 

 connects ; consequently the two latter, during the course of 

 further modification, from existing in greater numbers, Avill have 

 a great advantage over the less numerous intermediate variety, 

 and Avill thus generally svicceed in sujiplanting and exterminat- 

 ing it. 



AVe have seen in this chapter how cautious we should be 

 in concluding that the most different habits of life could not 

 graduate into each other ; that a bat, for instance, could not 

 have been formed by natural selection from an animal which 

 at first could only glide through the air. 



We have seen that a species may under new conditions of 

 life change its habits, or have diversified habits, Avith some very 



