Instinct can do it. Some birds, for example, employ both parents to rear the young. But elaborate instinctive compulsions are incompatible with intelligence. Father has to have a good selfish reason to stay, if Father has brains enough to be selfish.
In the case of man, the mechanism is simple: permanent sexuality. The human is never satisfied at any time of year. From this fact we derive the family, and hence the possibility of prolonged immaturity, and hence our cerebral cortex.
In the case of the Diomedean, there was migration. Each flock had a long and dangerous way to travel every year. It was best to go in company, under some form of organization. At journey’s end in the tropics, there was the abandon of the mating season — but soon the unavoidable trip back home, for the equatorial islands would not support many visitors for very long.
Out of this primitive annual grouping — since it was not blindly instinctive, but the fruit of experience in a gifted animal — there grew loose permanent associations. Defensive bands became co-operative bands. Already the exigencies of travel had caused male and female to specialize their body types, one for fighting, one for burden-bearing. It was, therefore, advantageous that the sexes maintain their partnership the whole year around.
The animal of permanent family — on Diomedes, as a rule, a rather large family, an entire matrilineal clan — with the long gestation, the long cubhood, the constant change and challenge of environment, the competition for mates each midwinter with alien bands having alien ways: this animal had every evolutionary reason to start thinking. Out of such a matrix grew language, tools, fire, organized nations, and those vague unattainable yearnings we call “culture.”
Now while the Diomedean had no irrevocable pattern of inborn behavior, he did tend everywhere to follow certain modes of life. They were the easiest. Analogously, humankind is not required by instinct to formalize and regulate its matings as marriage, but human societies have almost invariably done so. It is more comfortable for all concerned. And so the Diomedean migrated south to breed.
But he did not have to!
When breeding cycles exist, they are controlled by some simple foolproof mechanism. Thus, for many birds on Earth it is the increasing length of the day in springtime which causes mating: the optical stimulus triggers hormonal processes which reactivate the dormant gonads. On Diomedes, this wouldn’t work; the light cycle varies too much with latitude. But once the proto-intelligent Diomedean had gotten into migratory habits — and therefore must breed only at a certain time of the year, if the young were to survive — evolution took the obvious course of making that migration itself the governor.
Ordinarily a hunter, with occasional meals of nuts or fruit or wild grain, the Diomedean exercised in spurts. Migration called for prolonged effort; it must have taken hundreds or thousands of generations to develop the flying muscles alone, time enough to develop other adaptations as well. So this effort stimulated certain glands, which operated through a complex hormonal system to waken the gonads. (An exception was the lactating female, whose mammaries secreted an inhibiting agent.) During the great flight, the sex hormone concentration built up — there was no time or energy to spare for its dissipation. Once in the tropics, rested and fed, the Diomedean made up for lost opportunities. He made up so thoroughly that the return trip had no significant effect on his exhausted glands.
Now and then in the homeland, fleetingly, after some unusual exertion, one might feel stirrings toward the opposite sex. One suppressed that, as rigorously as the human suppresses impulses to incest, and for an even more practical reason: a cub born out of season meant death on migration for itself as wfell as its mother. Not that the average Diomedean realized this overtly; he just accepted the taboo, founded religions and ethical systems and neuroses on it — However, doubtless the vague, lingering year-round attractiveness of the other sex had been an unconscious reason for the initial development of septs and flocks.
When the migratory Diomedean encountered a tribe which did not observe his most basic moral law, he knew physical horror.
Drak’ho Fleet was one of several which have now been discovered by traders. They may all have originated as groups living near the equator and thus not burdened by the need to travel; but this is still guesswork. The clear fact is that they began to live more off the sea than the land. Through many centuries they elaborated the physical apparatus of ships and tackle, until it had become their entire livelihood.
It gave more security than hunting. It gave a home which could be dwelt in continuously. It gave the possibility of constructing and using elaborate devices, accumulating large libraries, sitting and thinking or debating a problem — in short, the freedom to encumber oneself with a true civilization, which no migrator had except to the most limited degree. On the bad side, it meant grindingly hard labor and aristocratic domination.
This work kept the deckhand sexually stimulated; but warm shelters and stored sea food had made his birthtime independent of the season. Thus the sailor nations grew into a very humanlike pattern of marriage and child-raising: there was even a concept of romantic love.
The migrators, who thought him depraved, the sailor considered swinish. Indeed, neither culture could imagine how the other might even be of the same species.
And how shall one trust the absolute alien?
XXI
“It is these ideological pfuities that make the real nasty wars,” said Van Rijn. “But now I have taken off the ideology and we can sensible and friendly settle down to swindling each other, nie?”
He had not, of course, explained his hypothesis in such detail. Lannach’s philosophers had some vague idea of evolution, but were weak on astronomy; Drak’ho science was almost the reverse. Van Rijn had contented himself with very simple, repetitious words, sketching what must be the only reasonable explanation of the well-known reproductive differences.
He rubbed his hands and chortled into a tautening silence. “So! I have not made it all sweetness. Even I cannot do that overnights. For long times to come yet, you each think the others go about this in disgusting style. You make filthy jokes about each other… I know some good ones you can adapt. But you know, at least, that you are of the same race. Any of you could have been a solid member of the other nation, nie? Maybe, come changing times, you start switching around your ways to live. Why not experiment a little, ha? No, no, I see you can not like that idea yet, I say no more.”
He folded his arms and waited, bulky, shaggy, ragged, and caked with the grime of weeks. On creaking planks, under a red sun and a low sea wind, the scores of winged warriors and captains shuddered in the face of the unimagined.
Delp said at last, so slow and heavy it did not really break that drumhead silence: “Yes. This makes sense. I believe it.”
After another minute, bowing his head toward stone-rigid T’heonax: “My lord, this does change the situation. I think — it will not be as much as we hoped for, but better than I feared — We can make terms, they to have all the land and we to have the Sea of Achan. Now that I know they are not… devils… animals — Well, the normal guarantees, oaths and exchange of hostages and so on — should make the treaty firm enough.”
Tolk had been whispering in Trolwen’s ear. Lannach’s commander nodded. “That is much my own thought,” he said.
“Can we persuade the Council and the clans, Flockchief?” muttered Tolk.
“Herald, if we bring back an honorable peace, the Council will vote our ghosts godhood after we die.”