|The How and Why of Channeling
This is an attempt to provide a genetic basis for the ability to channel. If you know nothing about genes, and you’re not interested, I suggest you skip this one. Otherwise, read on.
The basic theory
According to the Guide, 'the ability to channel is a genetic recessive.' So to begin with, let's say there is a single gene that controls channeling ability in anyone, male or female. Call the dominant allele T, and the recessive allele t. If, and only if, you possess two copies of the recessive t allele, can you channel. This is, in effect, a 'trigger' gene: there are other channeling-related genes, but without the tt genotype they have no effect. The scientific term is epistasis.
Now, we don't know for sure that strength in the Power is genetically determined, but we don't know that it isn't, either. The average Aes Sedai, at least, is significantly weaker now than during the Age of Legends, which is consistent with a genetic basis - fewer channelers are having children, so the strength alleles (see below) are rarer and less likely to coincide in one person. Besides, my 'Threads in the Pattern' theories don't work as well if strength is a property of the soul, so for this essay I'll assume it's genetic. Several genes collectively determine your potential strength in the Power. If there are n number of these genes ( 2n alleles ) there are 2n + 1 possible strengths. Jordan has said that strength works on a 21-point scale, so n = 10. Call them genes A to J.
The more dominant genes you have in this group, the stronger in the Power you have the potential to be. for example, if you have the genotype:
aa bb cc dd ee ff gg hh ii jj
then you are as weak in the Power as it's possible to be and still be a channeler (possibly Morgase's level). If you have the genotype:
AA BB CC DD EE FF GG HH II JJ
then you're either Rand, Nynaeve or one of the Forsaken. If you have about half the number of potential dominant alleles, such as:
aa Bb CC Dd ee FF Gg hh II jJ
you're somewhere in the middle. And so on.
Another gene determines whether or not you have the spark. Call this one S/s: if in the homozygous recessive state (ss) it kicks in if you have a certain number of strength alleles. If you don't have the ss genotype, though, you won't have the spark no matter how strong you are. This explains both why channelers with the spark are usually stronger, and why there are, despite this trend, a number of powerful channelers without it. The best example is Sharina, who does not have the spark despite being of maximum or near-maximum potential strength.
The next question is whether you channel saidar or saidin. For the sake of simplicity, I'll assume it's linked to the sex chromosomes. The presence of a Y chromosome means you channel saidin: otherwise, saidar. There are, of course, some irritating questions raised by this theory, concerning one Aran'gar.
Aran'gar is, as we all know, a male Forsaken recycled into a female body, who continues to channel saidin. A less-noticed point is that all four of the recycled Forsaken (Aran'gar, Osan'gar, Cyndane, Moridin) possess the same strength as they did in their previous bodies. The chances of finding four bodies with near-maximum strength (not to mention an apparently female body with a Y chromosome) is pretty unlikely, so we have to look for explanations.
(It is actually possible that the Aran'gar body has a Y chromosome. There's a condition known as AIS (androgen insensitivity syndrome) where a genetic male grows up as an outwardly normal but sterile female. AIS women are often physically superfeminine [full breasts, flawless skin, thick hair - they don't react at all to the male hormones that cause flat chests, acne and baldness, whereas normal women do react to the low levels in their bodies] and that certainly fits Aran'gar. As mentioned, though, it's not likely - AIS is rare.)
Most likely is that genes do not determine strength/Power half directly, but rather which half and what strength your mind will develop into channeling. An adult mind is already fully developed, so when transferred into another body will override that body's genes and continue in the pattern that has already formed.
If strength is genetic, we should see differences in the various cultures. Randland and Seanchan should be about equal for lowest frequency/average strength of channelers: in both cases men are usually taken out (killed or gentled, which is usually fatal anyway) at a young age. Even if a male channeler escapes notice, the taint is likely to kill him or render him infertile before he can have many children. In Seanchan, all female channelers are found; ones with the spark presumably don't have children, and we don't know whether sul'dam marry or not. I'd guess they do, though. In Randland, most with the spark and a fair percentage without are found, and most of those are removed from the gene pool (neither Aes Sedai nor Kin have children, so the only ones of this group who pass on their genes are girls who leave the Tower but do not join the Kin). Three out of four wilders die, and the remaining quarter often become Wisdoms or the equivalent; if the Two Rivers is typical of the wider world, Wisdoms don't usually marry or have children. However, the many without the spark who are not found are as likely to have children as any other women are.
The Aiel should have more and stronger channelers: Wise Ones do have children (possibly even more than normal women, as staying young for longer ought to increase years of fertility) and they sweep up all women with the ability to channel or learn to. However, many die in Rhuidean, and male channelers are also removed from the gene pool by leaving to fight the Dark One (and presumably dying in the attempt). We have no idea what happens to male channelers among the Atha'an Miere - most likely they, too, are killed or gentled - but Windfinders also have children. In fact, we have a specific appearance in the books of Windfinders who are mother and daughter, Caire and Talaan.
For obvious reasons, Shara should have the most channelers, and the strongest. Channelers are a separate class who don't marry outside it, moreover, male channelers (or at least the sons of female channelers, who are likely to have inherited the ability) are actually bred before being killed off at twenty-one or whenever they show signs of channeling. It's hardly a kind system, but if the goal is maximising the number of channelers, it makes sense. I therefore predict that if Shara ever makes an appearance in the books, Randlanders will discover an astonishing number of powerful channelers - possibly even similar average strength as in the Age of Legends, since Shara has been isolated since the Breaking.
Because I'm a nice person, here's a list of the channelers we know who are related to each other. I even worked out the percentage of DNA they have in common. Elayne and Moiraine are the only ones known to have the spark, and Morgase the only one known not to.
Morgase and Elayne: relationship, mother and daughter: 50%: one very weak, one very strong.
Moiraine and Elayne: relationship, half-aunt and niece: 12.5%: one fairly strong, one very strong.
Vandene and Adeleas: relationship, sisters: 50% (assuming they're full sisters - before anyone says anything, they are not identical twins, they just look like it): strength uncertain, probably around average for both.
Caire and Tebreille (the Windfinders): relationship, sisters: 50% (see above) both fairly strong.
Caire and Talaan: relationship, mother and daughter: 50%: one fairly strong, one extremely strong.
Tebreille and Talaan: relationship, aunt and niece: 25%: one fairly strong, one extremely strong.
Anyone who wants to work out the genotypes for these channelers is welcome. Also, for anyone interested in channeling and genetics (and with a fair bit of knowledge about the latter) Couladin from wheeloftime.com has written an essay on the same subject but in more detail. Read it.