like in kind, the progress of organization implies, not only that the units composing each differentiated part severally maintain their positions, but also that their progeny succeed to those positions. Bile cells which, while performing their functions, grow and give origin to new bile-cells, are, when they decay and disappear, replaced by these: the cells descending from them do not migrate to the kidneys, or the muscles, or the nervous centers, to join in the performance of their duties. And, evidently, unless the specialized units each organ is made of gave origin to units similarly specialized, which remained in the same place, there could be none of those settled relations among parts which characterize the organism and fit it for its particular mode of life.
In a society, also, fixity of structure is favored by the transmission of positions and functions through successive generations. The maintenance of those class-divisions which arise as political organization advances implies the inheritance of a rank and a place in each class. Obviously, in proportion as the difficulty of rising from one grade into another is great, the social grades become settled in their relations. The like happens with those subdivisions of classes which, in some societies, constitute castes, and in other societies are partially exemplified by guilds. Where custom or law compels the sons of each trader to follow his father's occupation, there result, among the structures carrying on production and distribution, obstacles to change analogous to those which result in the regulative structures from impassable divisions of ranks. India shows this in an extreme degree; and in a less degree it was shown by the craft-guilds of early days in England, which facilitated adoption of a craft by the children of those engaged in it, and hindered adoption of it by others. Thus we may call inheritance of position and function the principle of fixity in social organization.
There is another way in which succession by inheritance, whether to class-position or to occupation, conduces to stability. It secures supremacy of the elder; and supremacy of the elder tends toward maintenance of the established order. A system under which a chief-ruler, sub-ruler, head of a clan or house, official, or any person having the power given by rank or property, has his place filled up at death by a descendant, in conformity with some accepted rule of succession, is a system under which, by implication, the young, and even the middle aged, are excluded from the conduct of affairs. So, too, where an industrial system is such that the son, habitually brought up to his father's business, succeeds to his position when he dies, it follows in like manner that the regulative power of the elder over the processes of production and distribution is scarcely at all qualified by the power of the younger. Now, it is a truth daily exemplified that increasing rigidity of organization, necessitated by the process of evolution, produces in age an increasing strength of habit and aversion to change.