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Show 10 DARWINISM CHAP. Species should be carefully comidcrcd. It_ is ::~s follow~: "Althonu·h much remains obscure, and w1ll long rcmam obscure I can entertain no doubt, after the mo t deliberate and di;passionate judgment of wh_ich I am capable, _that th (• view which most naturali ts until recently cntertamcd and which I formerly entertained- namely, that each specie. has been independently created-is erroneous. I am fully convinced that species arc not immutable ; but that t.ho c bclon<ri.na to what arc called the same genera arc ]menl dcscc~da~ts of some other and generally extinct species, in the same manner as the acknowledged varietic of any one species are the descendants of th.at species. Furthcrmor~, J am convinced that Natural SelectiOn has 1 een the mo t mlportant, but not the exclusive, means of mo?ifi~ation. " . It should be especially noted that all which 1s here cb1mcd is now almost universally admitted, while the critici ms of Darwin's works refer almost exclusively to those numerous questions which, afl he himself says, " will long rcnutin obscure." The Dwrwinian Theory. As it will be necessary, in the following chapters, to set forth a considerable body of facts in almost every department of naturnJ history, in order to establish the fnnclamcntal propo itions on which the theory of natural election r ests, I propose to give a preliminary stat~ment of wha.t the theory really is, in order that the reader may better appr cia.te the necessity for discussing so many details, and ma.y thus feel a more enlightened interest in them. Many of the twts to he adducecl arc so novel and so cl'trious that they arc sure to he appreciated by every one who takes an interest in nature, but unless the need of them is clearly seen it may be thought that time is being wasted on mere curious details and strange facts which have little bearing on the question at issue. The theory of natural selection rests on two main classes of facts which apply to all organised beings without exception, and which thus take rank as fundamental principle or laws. The first is, the power of rapid multiplication in a geometrical progression; the second, that the offspring always vary slightly from the parents, though generally very closely rc ·cmblinu WHAT ARE SPE IES 11 them. From tho first fa?t or law there follows, necessarily, a constant struggle for existence ; because, while the offspring always exceed the parents in number, generally to an enormous ' extent, yet the total number of living organisms in the world does not, and cannot, increase year by year. Consequently every year, ?n the average, as m~n~ die ~s are born, plant. as I well as ammal ; and the maJonty chc premature deaths. They kill each other in a thousand different ways ; they . tarve each other by some consuming the food that others W<tnt ; they are destroyed largely by the powers of nature- by cold and heat, by rain and storm, by flood and fire. There is thus a perpetual struggle among them which shall live and which shall die ; and this struggle is tremendou ly severe, becau ·e so few can possibly remain alive-one in five, one in ten, often only one in a hundred or even one in a thousand. Then comes the questiQJJ, Why do some live rather than ot?ers.~ If all the individuals of each species were exactly ahke m every respect, we could only say it is a matter of chance. But they are not alike. We find that they vary in many different ways. Some are stronger, some swifter, some hardier in constitution, some more cunning. An ob. cure colour may render concealment more easy for some, keener sight may enable others to discover prey or escape from an enemy better than their fellows. Among plants the smallest differences may be useful or the rever e. The earlic. t and strongest shoots may escape the slug ; their greater vigour may enable them to flower and seed earlier in a wet autumn · plants best armed with spines or hairs may escape bcin~ devoured; those whose flowers are most conspicuous may be soonest fertilised by insects. We cannot doubt that, on the whole, any beneficial variations will give the possessors of it a greater probability of living through the tremendous ordeal they have to undergo. There may be something left to chance, but on the whole the .fittest 1cill surl:i ~·e. Then we have another important fact to con ider, the principle of heredity or transmis ion of variations. If we grow plants from seed or breed any kind of animals year after year, consuming or giving away all the increa c we llo not wish to keep just as they come to hand, our pl<tnts or animals will continue much the same ; but if every year we |