Furthermore, in addition to the historical difficulty, there is another strong reason for doubting the dependence of agnation upon _patria potestas_: the inconsistency of the latter in its effects upon kinship. If the descendants of married women are excluded from relationship, solely on the ground that they belong to another _potestas_, why, for the same reason, should not the children of men, say of brothers _sui juris_,[86] be likewise mutually excluded? Plainly some more satisfactory explanation of this remarkable discrimination between the sexes must exist. Such an explanation McLennan finds in exogamy, or the custom which forbids marriage between persons of the same group of acknowledged kindred.[87] It seems probable that in early times the patrician family was coextensive with the _gens_. _Agnatio_ and _gentilitas_ were equivalent expressions.[88] During the historical period, at any rate, _gentilitas_ is traced through the male line; and it is not impossible that originally inter-marriage was forbidden between those bearing the same gentile name.[89] In that case, agnation appears as the natural result of the gentile rule of exogamy, retained, after the weakening of the _gens_, for the regulation of succession within the family. Exogamy, however, does not necessarily imply the _patria potestas_, but is found more frequently perhaps with the maternal than with the paternal system of kinship.[90] In fact, for the Romans and kindred Italic tribes, considerable evidence has been collected by various writers pointing, as they believe, to an early transition from the maternal to the cognatic or the agnatic system.[91] While this conclusion may be rejected, it must nevertheless be admitted that criticism of the patriarchal theory has been very successful in its general results. It appears to have established beyond question the complex and highly artificial character of the Roman family.[92] So far from being the type of early social organization, it is seen to be relatively modern and ill fitted to the condition of primitive men. [86] MCLENNAN, _Patriarchal Theory_, 190. [87] _Ibid._, 194, 195. [88] _Ibid._, 204-14. _Cf._ MUIRHEAD, _Introduction to the Private Law of Rome_, 43. [89] PLUTARCH, _Roman Questions_, VI, tells us that "in early times the prohibition of marriage extended as far as the tie of blood; and, if this be received, it involves--since the gentiles considered themselves to be of the same blood--that there could not be marriage between persons of the same gens."--MCLENNAN, _op. cit._, 206, 207.