In geography, isolation denotes separation in space. In sociology, the essential characteristic of isolation is found in exclusion from communication. Geographical forms of isolation are sociologically significant in so far as they prevent communication. The isolation of the mountain whites in the southern states, even if based on spatial separation, consisted in the absence of contacts and competition, participation in the progressive currents of civilization. Biological differences, whether physical or mental, between the different races are sociologically important to the extent to which they affect communication. Of themselves, differences in skin color between races would not prevent intercommunication of ideas. But the physical marks of racial differences have invariably become the symbols of racial solidarity and racial exclusiveness. The problems of humanity are altogether different from what they would have been were all races of one complexion as they are of one blood. Certain physical and mental defects and differences in and of themselves tend to separate the individual from his group. The deaf-mute and the blind are deprived of normal avenues to communication. "My deafness," wrote Beethoven, "forces me to live in exile." The physically handicapped are frequently unable to participate in certain human activities on equal terms with their fellows. Minor physical defects and marked physical variations from the normal tend to become the basis of social discrimination. Mental differences frequently offer still greater obstacles to social contacts. The idiot and the imbecile are obviously debarred from normal communication with their intelligent associates. The "dunce" was isolated by village ridicule and contempt long before the term "moron" was coined, or the feeble-minded segregated in institutions and colonies. The individual with the highest native endowments, the genius, and the talented enjoy or suffer from a more subtle type of isolation from their fellows, that is, the isolation of eminence. "The reason of isolation," says Thoreau, a lover of solitude, "is not that we love to be alone, but that we love to soar; and when we soar, the company grows thinner and thinner until there is none left." So far, isolation as a tool of social analysis has been treated as an effect of geographical separation or of structural differentiation resulting in limitation of communication. Social distances are frequently based on other subtler forms of isolation. The study of cultural differences between groups has revealed barriers quite as real and as effective as those of physical space and structure. Variations in language, folkways, mores, conventions, and ideals separate individuals and peoples from each other as widely as oceans and deserts. Communication between England and Australia is far closer and freer than between Germany and France.