. Evolution and its relation to religious thought . GEOGRAPHICAL DISTRIBUTION. 1^1 continuous. There would, it is true, be some local varia-tions dependent upon soil and humidity, etc., but sub-stantially the same species would exist all around. Thedistribution would be almost wholly zonal. But the in-teryening oceans are complete barriers to continentalspecies. Hence we ought to expect, and do find, that thefaunas and floras of different continents are almost to-tally apparentlyoriginated on itsown continent,and did notspread to othercontinents, onlybecause theycould not getthe
. Evolution and its relation to religious thought . GEOGRAPHICAL DISTRIBUTION. 1^1 continuous. There would, it is true, be some local varia-tions dependent upon soil and humidity, etc., but sub-stantially the same species would exist all around. Thedistribution would be almost wholly zonal. But the in-teryening oceans are complete barriers to continentalspecies. Hence we ought to expect, and do find, that thefaunas and floras of different continents are almost to-tally apparentlyoriginated on itsown continent,and did notspread to othercontinents, onlybecause theycould not getthere. It is ne-cessary to explainthis in more de-tail. Fig. 6(j repre-sents a polar yiewof the earth, showing the eastern and western conti-nents, and the five temperature zones already , if we examine the sj^ecies in each region, com-mencing at the pole, we find that those of Nos. 5and 4 are almost identical all around. The reason isobvious. The continents come close together there,with ice-connection if not land-connection all Fig. 66.—Polar projection of the earth. 1, tropi-cal ; 2, temperate ; 3, sub-arctic ; 4, arctic;5, polar regions. 172 EVIDENCES OF THE TRUTH OF EVOLUTION. There is but one circumpolar region. But, as soon aswe come down to No. 3 and No. 2, the species on thetwo continents are nearly all different, because thereis an impassable barrier between, either in the form ofocean or of Arctic cold. For example, the animals andplants inhabiting the United States are almost whol-ly different from those in Europe, not only in species,but even largely in genera and to some extent in are some exceptions to this rule, but these are ofthe kind which prove the rule, or rather the principle onwhich the rule is founded. These exceptions are mainlyof three kinds : 1. Introduced si^ecies.—All our weeds,many garden-plants, and many animal pests are of thiskind. They were not found here when America wasdiscovered, only because they could
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