Immediately after him, in 1871, Morgan appeared with fresh and, in many respects, conclusive material. He had convinced himself that the peculiar system of kinship in vogue among the Iroquois was common to all the aborigines of the United States, and practised all over the continent, although it was in direct contradiction with all the degrees of relation arising from the connubial system in practice there. He prevailed on the federal government to collect information on the systems of kinship of other nations by the help of question blanks and tables drawn up by himself. The answers brought the following results:
1. The kinship system of the American Indians is also in vogue in Asia, and in a somewhat modified form among numerous tribes of Africa and Australia.
2. This system finds a complete explanation in a certain form of communal marriage now in process of decline in Hawaii and some Australian islands.
3. By the side of this marital form, there is in practice on the same islands a system of kinship only explicable by a still more primeval and now extinct form of communal marriage.
The collected data and the conclusions of Morgan were published in his "Systems of Consanguinity and Affinity," 1871, and discussion transferred to a far more extensive field. Taking his departure from the system of affinity he reconstructed the corresponding forms of the family, thereby opening a new road to scientific investigation and extending the retrospective view into prehistoric periods of human life. Once this view gained recognition, then the frail structure of McLennan, would vanish into thin air.
McLennan defended his theory in the new edition of "Primitive Marriage" (Studies in Ancient History, 1875). While he himself most artificially combines into a history of the family a number of hypotheses, he not only demands proofs from Lubbock and Morgan for every one of their propositions, but insists on proofs of such indisputable validity as is solely recognized in a Scotch court. And this is done by the same man who unhesitatingly concludes that the following people practiced polyandry: The Germans, on account of the intimate relation between uncle and nephew (mother's brother and sister's son); the Britons, because Cesar reports that the Britons have ten to twelve women in common; barbarians, because all other reports of the old writers on community of women are misinterpreted by him! One is reminded of a prosecuting attorney who takes all possible liberty in making up his case, but who demands the most formal and legally valid proof for every word of the lawyer for the defense.
He asserts that communal marriage is purely the outgrowth of imagination, and in so doing falls far behind Bachofen. He represents Morgan's systems of affinity as mere codes of conventional politeness, proven by the fact that Indians address also strangers, white people, as brother or father. This is like asserting that the terms father, mother, brother, sister are simply meaningless forms of address, because Catholic priests and abbesses are also addressed as father and mother, and monks and nuns, or even free-masons and members of English professional clubs in solemn session, as brother and sister. In short, McLennan's defense was extremely weak.
One point still remained that had not been attacked. The contrast of exogamous and endogamous tribes, on which his whole system was founded, was not only left unchallenged, but was even generally regarded as the pivotal point of the entire history of the family. It was admitted that McLennan's attempt to explain this contrast was insufficient and in contradiction with the facts enumerated by himself. But the contrast itself, the existence of two diametrically opposed forms of independent and absolute groups, one of them marrying the women of its own group, the other strictly forbidding this habit, was considered irrefutable gospel. Compare e. g. Giraud-Teulon's "Origines de la famille" (1874) and even Lubbock's "Origin of Civilization" (4th edition, 1882).
At this point Morgan's main work, "Ancient Society" (1877), inserts its lever. It is this work on which the present volume is based. Here we find clearly demonstrated what was only dimly perceived by Morgan in 1871. There is no antithesis between endogamy and exogamy; no exogamous "tribes" have been found up to the present time. But at the time when communal marriage still existed—and in all probability it once existed everywhere—a tribe was subdivided into a number of groups—"gentes"—consanguineous on the mother's side, within which intermarrying was strictly forbidden. The men of a certain "gens," therefore, could choose their wives within the tribe, and did so as a rule, but had to choose them outside of the "gens." And while thus the "gens" was strictly exogamous, the tribe comprising an aggregate of "gentes" was equally endogamous. This fact gave the final blow to McLennan's artificial structure.
But Morgan did not rest here. The "gens" of the American Indians furthermore assisted him in gaining another important step in the field under investigation. He found that this "gens," organized in conformity with maternal law, was the original form out of which later on the "gens" by paternal law developed, such as we find it among the civilized nations of antiquity. The Greek and Roman "gens," an unsolved riddle to all historians up to our time, found its explanation in the Indian "gens." A new foundation was discovered for the entire primeval history.