ABSTRACT
This chapter discusses some of the difficulties and objections which may be urged against the theory of natural selection. As natural selection acts solely by the preservation of profitable modifications, each new form will tend in a fully-stocked country to take the place of, and finally to exterminate, its own less improved parent-form and other less favoured forms with which it comes into competition. Thus extinction and natural selection go hand in hand. In looking at species as they are now distributed over a wide area, one generally finds them tolerably numerous over a large territory, then becoming somewhat abruptly rarer and rarer on the confines, and finally disappearing. Hence the neutral territory, between two representative species is generally narrow in comparison with the territory proper to each. On the theory of natural selection one can clearly understand the full meaning of that old canon in natural history, Natura non facit saltum.
