of the English race has been distinctly modified by residence in the United States of America.  It is not more than two and a half centuries since Englishmen began to emigrate in any considerable numbers to the American Continent, but in that comparatively short period the Anglo-American has ceased to resemble his ancestors in physical appearance.  Alterations have taken place in the skin, the hair, the neck, and the head; the lower jaw has become bigger; the bones of the arms and legs have lengthened, and the American of to-day requires a different kind of glove from the Englishman.  Structural changes of a similar character have taken place in the negroes transplanted to America.  M. Elisee Reclus considers that in a century and a half they have traversed a good quarter of the distance which separates them from the whites.  Another important point, as showing the influence of habitat upon race, is the fact that the modifications of human structure resulting from residence in America are in the direction of assimilating the European type to that of the red man.[11] In short, it may be taken as a well-established principle that external nature destroys all organisms that cannot adapt themselves to its action, and physiologically modifies all organisms that can.

    [11] The various types of Jews also afford a striking instance of
    the effect of natural surroundings on bodily structure.

The social condition of mankind is also profoundly affected by climatic and other external circumstances.  The intense cold of the Arctic and Antarctic regions is fatal to anything approaching a developed form of civilisation.  Intense heat, on the other hand, although not incompatible with a certain degree of progress, is unfavourable to its permanence;[12] the extinct societies of the tropics, such as Cambodia, Mexico and Peru, affording instances of the operation of this law.  It is impossible for man to get beyond the nomad state in the vast deserts of Northern Africa; and the extreme moisture of the atmosphere in other portions of the same continent puts an effectual check on anything like social advance.  In some parts of the world social development has been hindered by external circumstances of another character, such as the want of wood, the scarcity of animals, the absence of edible fruits.  In fact, it is only within a comparatively temperate zone that human society has been able permanently to assume highly complex forms and to build itself up on an extensive scale.  In this zone, climate, while favouring man up to a certain point, has at the same time compelled him to eat bread in the sweat of his brow.  It has compelled him to enter into conflict with natural obstacles, the result of which has been to call forth his powers of industry, of energy, of self-reliance, and to sharpen his intellectual faculties generally.  In addition to exercising and strengthening these personal attributes, the climatic influences of what has been called the zone of civilisation have brought