Pon farr is a hodge-podge concept and as such tends to defy reasonable explanation. However, as sexuality is vitally important to any society with gender divisions, "Vulcan biology" as Spock shyly put it is vitally important to developing a framework for how the Vulcan societies operate.
Beware, longish post, partly in reply to Triumphant, and parly my own diatribe. For the biologically-minded, you might find it interesting, or find some things to argue with. There is also a great penis joke buried near the bottom.
At the age of 14, they enter Pon Farr again, and become "married" (which I suspect is a poor English translation of the Vulcan word for the state) since their bodies are mature enough for sexual activity. A "priestess" and several others are on hand during this and every subsequent Pon Farr for reasons that are not entirely clear - but I would think are something aside from, "hey, free porn!"
Providing instruction or even applying technology, or making certain participants are unharmed, or providing ... additional genetic material, shall we say ... to attempt to help ensure a pregnancy when that is desired. That isn't generally our way, but hey, these
are aliens.
Hm, have to disagree with you there. This sort of thing is evolutionarily unlikely. Vulcans are already portrayed as ultrapossessive, homicidal beyond even Terran mammal standards, as far as intragender sexual conflict goes, and generally any individual that permitted that kind of
prima nocta situation would be selected against in favor of more aggressive, more possessive bridegrooms. This kind of cuckolding works on Earth--and even then usually poorly--when the machinery of the state permits authorities to abuse the delegated force of the society as a whole to set themselves up as artificial alpha males. And no one except the cuckolder is
happy with it, as the female has been deprived of meaningful reproductive choice and any mate she has has been deprived of his ability to pass on his own genes for nine or more months. I doubt, especially under a Surakian social paradigm valuing harmony and eschewing the abuse of authority, this kind of tradition could possibly be perpetuated.
Pregnancies may (or may not) be good for society no matter how they are come to, but outside of exceptional circumstances of reproductive-caste eusociality and haplodiploid sister-relatedness seen in hymendopterans (ants) and some other, limited groups of animals, individuals of any species should ordinarily be programmed to propagate their own genes, not the group's.
What's Love Got To Do With It?
In many arranged marriages on Earth, the couples do grow to have an affection - love - for one another. I would assume this is the same for Vulcan pairings. Also, in the event of premature death of one half of a pairing, the biological drive will still be there every 7 years, and it is possible that love, or at least affection, plays some role in the choices made for these older betrothals. And then there are Vulcans that choose to mate with aliens. They are stone
freaks, and their logic may be a bit questionable as regards why they would make such a choice.
I suspect that Sarek chose Amanda because of the ping-pong ball trick.
Good ref.
You know, it occurs to me that, by the rules of "Amok Time," Sarek almost definitely had been betrothed a long time before he'd ever met Amanda (maybe a long time before Amanda had ever been born!). I wish I'd thought of this when arguing for the merits of The Final Frontier--so many people think it's some kind of canon violation that Spock has this brother, when, really, by the very necessities of Vulcan life laid out
explicitly in the canon, it would almost be more surprising if Spock
didn't have a fully Vulcan brother out there. And even in the case of futuristic birth control, it would be truly baffling if Sarek, from a politically important family and hence presumably a hot property for the marriage brokers, would not have had a previous wife.
If we accept the presumption that Vulcans are not polygamous, or at least that Sarek is not legally married to two wives, we can even deduce something further from these facts: namely, that Vulcans will not just marry for love, but
will divorce when there is not love in a relationship.
However,
should we presume that Vulcans are not polygamous? It seems likely that in the olden days they were, as left to their own devices, males seem to fatally compete with each other often enough to drive down the sex ratio. (However, if they are like humans in this regard, a ~10% fatality rate in males would actually
even the at-birth ratio, ~105:100.)
The social adaptations of Vulcans--namely arranged marriage--seem to indicate that even pre-Surak Vulcand realized that such intragroup conflict had to be contained, so established the concept of arranged marriages to nicely pair off every child. Societies that did this would be able to keep their men from killing each other and have a selective advantage over societies which did not. Arranged marriage or at least the concept of marriage as ownership were likely to have been very early social inventions.
They were on Earth, and performed the very same social function--keeping tribes from shearing apart due to sexual conflict. I suspect that on the biological level, the expression of genes for homosexuality may also fill this function, but let's not derail this thread with that. Michel Houellebecq, French novelist, is famous for (often obscenely) theorizing that modern sexual mores are permitting the reemergence (if he did ever truly submerge) of the dominant alpha male in human coupling, which along with other factors is causing a great deal of misery. The notion is that any society which permits the creation of a free sexual market will produce "rich" and "poor," and generate a type of class conflict that is dependent not on material wealth but sexual success.
There is a very strong possibility, however, that females are not the limited sex amongst Vulcans. Vulcan males undergo pon farr every seven years. This would presumably correspond--Tuvok's kids notwithstanding--to a fertility cycle. If Vulcan females are capable of pregnancy at any given time, then even with the development period placental females are saddled with, they would strangely still be capable of more sexual fitness than the men. This would throw a wrench into entire notion of mapping human socio-sexual dynamics onto Vulcans, and bring into frame a strong evolutionary incentive for polyandry. There is some nebulous fanon that posits a matriarchal Vulcan society, but evidence that Vulcan females seek other mates would actually provide firm support for that deduction. Maybe one of Tuvok's kids just ain't his.
Edit: Incidentally, although "sex is fun" is as good an reason as any, this would provide a deeper explanation as to why in "The Enterprise Incident," Spock and the Romulan commander both seemed sexually responsive, even though neither were in pon farr. For the Romulan commander's part, sexual responsiveness suggests large fertility windows, possibly even permanent ones (there is nothing that says Vulcan females have to have an ovarian cycle, and it could easily be the other way around, an egg or eggs flushed into a contained organ full of sperm).
As for Spock, it's possible that Vulcan males could "fake" active gametic material whenever they were not fertile, in order to fool their mates when they have already used their brief window to pursue fitter females. This would be analogous to cryptic female choice in some Terran animals, e.g., many birds as well as hyenas, who are able to dump unwanted partners' sperm, preventing them from being tied up with some loser's kid.
Can this polyandry be squared with the koon-ut-kal-i-fee? It could. Vulcan males would still have a vested interest in preempting their females from wasting resources on genes not their own, as well as forestalling the possibility of their females from dying in childbirth (an acceptable risk if it means life for their own children, but not for others' offspring). So fighting for proprietorship of the womb would be natural. It would be equally natural for females to permit cuckoldry (which would be blindingly obvious cuckoldry if the seven year cycle is one for fertility), so it would be a constant struggle between male and female for control of the baby parts.
Koon-ut-kal-i-fee is an interesting hybridization of classic male-versus-male and female choice paradigms of sexual conflict. It may serve as a social convention that permits females to choose the "best but only," as determined by the outcome of the fight, which would be a compromise between the drive for polyandry in the female, providing her with the fittest specimen available for breeding, and the male, who would have eliminated at least one competitor for the womb. It could have persisted in the post-Surak era, as even Vulcan Jesus could not easily find a workaround for the selfish gene.
Obviously, no system of monogamy is foolproof, because it is fundamentally artificial, just as any restraint on a free market, whether for good or ill, is artificial, and polyandry could be common and tolerated in the same vein that human male "indiscretions" have traditionally been better-tolerated than human female "promiscuity". I.e., Tuvok just keeps believing she'll change.
However, the psychic bonding of monogamous partners, perhaps only possible after Surakian discipline, could make polyandry much harder to get away with, especially for the trespassing male, who would likely bear the brunt of the inevitably violent response, tightening a noose on female reproductive choice. Surak was misquoted--he said "
my dick."
And I won't even get started on how all this might apply on Romulus.
At any rate, getting back to Sarek again, what's the deal with his pon farr? He's schtupping a red-blooded round-ear, but it's biologically retarded to say that pon farr could be satisfactorily resolved through that. (I'm looking at you,
Voyager.) If this were the case, no sehlat on Vulcan would be safe. The answer must be that Sarek
is polygamous, but not legally so. I am convinced he is getting some on the side. Nu-Uhura, watch out. Sylar's going to be a bounder come every seven years.
"Biologically retarded"? WTF?! It would be biologically retarded to suggest that there is any difference between having sex with a human or with a Vulcan. Sex is sex, and they obviously have the same reproductive organs. Or else they wouldn't be able to have babies. So, again, what on Vulcan are you talking about? 
) and that they were headed for Vulcan. Logic has nothing to do with Pon Farr, and duty is exactly why he changed his mind and did not go through with it. Personally, I think Spock would have prefered to have sex with Chapel or Uhura if that was all there was to it, but he 'needed' to do it with T'Pring and only T'Pring because she is his 'bethroted'. In his mind, he is a "married" man, and it would not have been right to have a fling with a human woman. Spock was always trying to be a good Vulcan, and Vulcan traditions meant much to him. That is totally in character for him. 
