Though the "filial and fraternal affections may be instinctive," they are "obviously independent of any theory of kinship, its origin or consequences; they are distinct from the perception of the unity of blood upon which kinship depends; and they may have existed long before kinship became an object of thought." Such a group may have been held together chiefly "by the feeling of kindred;" but the "apparent bond of fellowship ... would be that they and theirs had always been companions in war or the chase--joint-tenants of the same cave or grove."[239] Slowly the idea of blood-relationship arose; and eventually observation led to a recognition of the system of kinship through the mother. Further than this, so long as paternity remained uncertain, primitive men could not go. For the theory in question, therefore, the maternal system of kinship existing in the homogeneous "group-stock" is the social fact of fundamental importance. But primitive man was rude, ignorant, relatively helpless. "Before the invention of the arts, and the formation of provident habits, the struggle for existence must often have become very serious. The instincts of self-preservation, therefore, must have frequently predominated." Society would tend toward one common type in which there was little place for the "unselfish affections." In this "struggle for food and security" the balance of the sexes would be disturbed. "As braves and hunters were required and valued, it would be to the interest of every horde to rear, when possible, its healthy male children." The weaker sex must obey the cruel law requiring the "survival of the fittest." Hence arose the common, perhaps general, practice of female infanticide.[240] The result of this disturbance of the balance of the sexes, caused by female infanticide, was a series of customs or phenomena of great sociological interest, requiring notice in the order in which they are supposed to have arisen. [239] MCLENNAN, _op. cit._, I, 83, 84. [240] _Ibid._, 90, 91, 75-77; II, 77-80. After the appearance of totem groups, infanticide would be checked by the blood-feud: _ibid._, I, 145.