Both Mr. Morgan and Mr. McLennan have drawn attention to the peculiarities in the terms of address as between 'brothers' and as between 'sisters.' It is curious that the full significance of the phenomena therein presented escaped two such keen intellects. We find here that terms of address as between persons of the same sex and of the same generation, and ergo brothers or sisters, present the very remarkable features that
(1) 'The age of the person spoken to compared with that of the speaker plays a very important part in the matter of denomination.'
(2) 'Such names refer not to the absolute age of the person addressed.'
(3) 'The relationships of brother and sister are conceived in the twofold form of elder and younger, and not in the abstract, and there are special terms for each among the Seneca Iroquois.'
(4) 'There is no name for brother and sister (Malayan system). On the other hand, there are a variety of names for use in salutations between "brother" and "sister" according to the age and sex of the person speaking in relation to the age and sex of the person addressed.'
(5) Among the Eskimo the form of the terms of relationship appears to depend, in some cases, more on the sex of the speaker than on that of the person to whom the term refers.
(6) In Eastern Central Africa, if a man has a brother and a sister, he is called one thing by the brother, but quite a different thing by the sister.
We will now illustrate the idea more completely by an extract of terms from the table of Hawaiian relationships in Ancient Society. An older or a younger brother is to a sister simply addressed or mentioned by the general term Kaiku nana, but to her, in address or mention of an older or a younger sister, they are respectively Kaik a'ana and Kaika-i-na. Again, an older or a younger sister is to a brother collectively Kaikuwaheena, but to him an elder or a younger brother is respectively Kaiknana and Kaikaina.
Now in view of our argument as regards the origin of these diversities in some sexual feelings, it is a most significant feature in these details of the terms of address that the expression of the relativity of age between the speakers is confined solely to the intercourse between members of the same sex. That a brother is the senior or the junior of Ego is carefully noted, but a sister is simply and vaguely a sister. Why? simply because whereas, by virtue of the primal law, no possible question whatever of mutual interest in sexual matters could possibly arise between a brother and a sister, on the other hand friction might hourly occur between brothers or between sisters. In fact, if our theory is correct, then, as questions of sexual privilege or precedence could cause jealousy between members of the same sex, distinctions would be necessary by definition of seniority when address took place between these, and in these cases alone, and this indeed we find to be the fact. As conclusive evidence we would cite the further important fact that these very same distinctions of senior and junior are used, inter se, between all those of the same totem [phratry] as now existing, but are never employed for their tribal cousins of the other totem [phratry]. And the reason is the same. The latter naturally do not marry (in groups formed of only two classes) [phratries] into the same totem [phratry] as the former, and thus there is no cause for jealousy or necessity of definition, whereas individuals of the same totem [phratry] are ipso facto group [potential] husbands of the same group [potential] wives, or are at least eligible in marriage with the same totem groups [phratries], and hence necessity for the exact definition by age of each one's rights.
Thus, as with other laws or institutions we have traced, we find a desire for distinction as regards rights in sexual union to be the genetic cause of the classificatory system both as regards the generation and its component members.