every period of their lives regardless of whether they are fit or not. Under such circumstances the death-rate almost invari- ably becomes enormous: only the most vigorous and intelligent mothers can survive, only those who have the most endurance, initiative, and spirit of adventure; and among the children only those who are exceptionally bright, vigorous, and attractive. As a rule the personal attractiveness of the child, which is merely another name for its degree of mental alertness and physical per- fection, counts greatly; for the attractive child is carried by the adults when it is tired, fed when it is hungry, given the best place to sleep, and in almost every way given advantages and chances for preservation which are denied to the stupid, crying, unattrac- tive child. And the same is true of the women, for those who are most attractive, which in general means those who are not only most perfect physically but most alert mentally, are the ones whom the men are most willing to help; and they are like- wise the ones who do not give up and die or fall by the wayside and allow themselves to become the captives of the enemy. Thus a hard migration of a whole community means that the process of natural selection is at work with great vigor to weed out all who are weak and to preserve a remnant who are espe- cially capable. Among the Brahmans we have no record of this, but in later periods we shall see the intimate details of the selec- tion which is even now altering the character of races.

It was presumably due in considerable measure to this strin- gent process of natural selection that the Brahmans who reached India were able to conquer the earlier inhabitants and impose themselves as a ruling class which later became a caste. To this may also have been due much of the unusual genius which enabled the people of India to evolve two new religions, Bud- dhism and Hinduism, to frame a new social system, to devise a noteworthy type of art and architecture, and to write a series of great poems which cause Sanskrit literature to rank among the greatest of those developed among primitive people.

The Khmers appear to have been an offshoot of these compe- tent Brahmans in the days when the original ability of that peo- l l