Herbivores meeting with new beasts of prey would, in some cases, be led intomodes of defence or escape differing from those previously used; and simultaneouslythe beasts of prey would modify their modes of pursuit and attack. We knowthat when circumstances demand it, such changes of habit do take place inanimals; and we know that if the new habits become the dominant ones, theymust eventually in some degree alter the organization. Note, now, a furtherconsequence. There must arise not simply a tendency towards the differentiationof each race of organisms into several races; but also a tendency to theoccasional production of a somewhat higher organism. Taken in the mass, thesedivergent varieties, which have been caused by fresh physical conditionsand habits of life, will exhibit alterations quite indefinite in kind anddegree, and alterations that do not necessarily constitute an advance. Probablyin most cases the modified type will be not appreciably more heterogeneousthan the original one. But it must now and then occur that some divisionof a species, falling into circumstances which give it rather more complexexperiences, and demand actions somewhat more involved, will have certainof its organs further differentiated in proportionately small degrees --will become slightly more heterogeneous. Hence, there will from time to timearise an increased heterogeneity both of the Earth's flora and fauna, andof individual races included in them. Omitting detailed explanations, andallowing for qualifications which cannot here be specified, it is sufficientlyclear that geological mutations have all along tended to complicate the formsof life, whether regarded separately or collectively That multiplicationof effects which has been a part-cause of the transformation of the Earth'scrust from the ****** into the complex, has simultaneously led to a paralleltransformation of the Life upon its surface.(*)<fn* Had this paragraph,first published in the Westminster Review in April, 1857, been writtenafter the appearance of Mr. Darwin's work on The Origin of Species,instead of before, it would doubtless have been otherwise expressed. Referencewould have been made to the process of "natural selection," asgreatly facilitating the differentiations described. As it is, however, Iprefer to let the passage stand in its original shape; partly because itseems to me that these successive changes of conditions would produce divergentvarieties or species, apart from the influence of "natural selection"(though in less numerous ways as well as less rapidly); and partly becauseI conceive that in the absence of these successive changes of conditions,"natural selection" would effect comparatively little. Let me addthat though these positions are not enunciated in The Origin of Species,yet a common friend gives me reason to think that Mr. Darwin would coincidein them.
The deduction here drawn from the established truths of geology and thegeneral laws of life, gains immensely in weight on finding it to be in harmonywith an induction drawn from direct experience. Just that divergence of manyraces from one race, above described as continually occurring during geologictime, we know to have occurred during the pre-historic and historic periods,in man and domestic animals. And just that multiplication of effects whichwe concluded must have been instrumental to the first, we see has in greatmeasure wrought the last. Single causes, as famine, pressure of population,war, have periodically led to further dispersions of men and of dependentcreatures: each such dispersion initiating new modifications, new varieties.
Whether all the human races be or be not derived from one stock, philologyshows that in many cases a group of races, now easily distinguishable fromone another, was originally one race -- that the diffusion of one race intodifferent regions and conditions of existence has produced many altered formsof it. Similarly with domestic animals. Though in some cases, as that ofdogs, community of origin will perhaps be disputed, yet in other cases, asthat of the sheep or the cattle of our own country, it will not be questionedthat local differences of climate, food, and treatment, have transformedone original breed into many breeds, now become so far distinct as to produceunstable hybrids. Moreover, through the complication of effects flowing fromsingle causes, we here find, what we before inferred, not only an increaseof general heterogeneity, but also of special heterogeneity. While of thedivergent divisions and subdivisions of the human race, many have undergonechanges not constituting an advance; others have become more heterogeneous.
The civilized European departs more widely from the mammalian archetype thandoes the Australian. §160. A sense-impression does not expend itself in arousing somesingle state of consciousness; but the state of consciousness aroused ismade up of various represented sensations connected by co-existence or sequencewith the presented sensation. And that, in proportion as the grade of intelligenceis high, the number of ideas suggested is great, may be readily inferred.
Let us, however, look at the proof that here, too, each change is the parentof many changes and that the multiplication increases in proportion as thearea affected is complex.
