Heritability of Eye-color in Roshar

[LordSolar]

It is mentioned very early on that marriages between high ranking darkeyes and low ranking lighteyes are not unheard of, has the heritability of eye-color ever been addressed in any of the many AMAs Sanderson has done?

In the event of a hypothetical marriage between a lighteyes of the 10th dahn and a darkeyes of the 1st nahn what would the probability be that a child would be lighteyed verses dark, and would the child's social rank depend on phenotypical eye-color?

[Nightslug]

Not sure about the rest but the fact that a darkeyes is of the 1st nahn does not indicate that they have any more chance at having a lighteyed child than a darkeyes of the lowest nahn. 

A darkeyes can move up and down in nahn. It is a sociological rather than a biological difference. 

As for the ranking of a lighteyes and a darkeyes child - it would efinitely depend on whether they were born with light or dark eyes. Hesina is darkeyed, yet has ties to Alethi nobility - she is still a darkeyes. 

Something I was reminded of recently is that the terms darkeyes and lighteyes has less to do with the colour of the eyes, than it has to do with the brightness (or radiance lol) of the eyes. So you can have a lighteyes with brown eyes and a darkeyes with green eyes. 

[cometaryorbit]

13 hours ago, LordSolar said:

It is mentioned very early on that marriages between high ranking darkeyes and low ranking lighteyes are not unheard of, has the heritability of eye-color ever been addressed in any of the many AMAs Sanderson has done?

In the event of a hypothetical marriage between a lighteyes of the 10th dahn and a darkeyes of the 1st nahn what would the probability be that a child would be lighteyed verses dark, and would the child's social rank depend on phenotypical eye-color?

The likeliest outcome is one eye light/one dark, and yes, social rank depends on actual eye color; tenth dahn is a likely result

Quote

Isilel

Or, and another thing—what happens if a lighteyed child is born to darkeyes or even slaves? Which should happen often enough, given that male nobles seem rather promiscuous. Anyway, are such people automatically of tenth dahn?

Brandon Sanderson

The situation is very much taken into account in these sorts of cases. Normally—if there is such a thing as normal with this—one question that's going to come up is are they heterochromatic. Because you can end up with one eye of each color, both eyes light, or both eyes dark. That's going to influence it a lot, what happens here. Do you have any heirs? Was your child born lighteyed? This sort of thing is treated the same way that a lot of societies treated illegitimate children. The question of, do I need this person as an heir? Are they born darkeyed? Can I shuffle them off somewhere? Set them up, declare them to be this certain rank. Are you high enough rank to do that? Are you tenth dahn yourself? What happens with all of these things? There's no single answer to that. The most common thing that's probably going to happen is that they are born heterochromatic. Then you're in this weird place where you're probably declared to be tenth dahn, but you may have way more power and authority than that if one parent is of a very high dahn, just as a bastard child in a royal line would be treated in our world.

Tor.com The Way of Kings Re-Read Interview (June 10, 2014)

(Part of an even longer WoB about the nahn/dahn system)

[Returned]

I'd think that the guiding principal is wealth more than eye color, as wealth seems to be how Alethi move up in station (Gaz mentions to someone, I think Shallan, that his nahn is what it is because he never managed to buy himself anything better). You're sorted directly into one of two groups based on eye color, but circumstances vary wildly within each set of dahns/nahns. For that to stably be the case for millennia it must be true that eye color is pretty strongly heritable. We just don't hear anything about darkeyed families suddenly having lighteyed children (or the reverse for lighteyed families), and even when that does happen the assumption would be infidelity.

Especially in Rhythm we see that social privileges are pretty light for a tenth dahn lighteyes, though they can certainly command more formal and informal support from society than could even a first nahn darkeyed citizen. A first nahn citizen probably is wealthier than a tenth dahn citizen, and while the latter would get all kinds of official deference (especially from strangers) I'd bet that the former lives better and has more practical influence over the world. And while a highprince might be able to disparage Redin to his face, woe betide a lower-dahn lighteyes (read: far less wealthy) who tried the same.

[cometaryorbit]

I agree that lighteyes and darkeyes are very hereditary, I think weirdness only arises if one parent is each (or maybe grandparents etc).

It does not seem to work like Earth eye colors- heterochromatic eyes being "the most common thing that's probably going to happen" from a lighteye/darkeye couple is very different from our eye color genetics.

Given that dark violet, and I think green, eyes are mentioned, I think it's very possible that lighteyed eyes are something we don't see on Earth, of specifically magical origin.

As for wealth... it's complicated... the full WOB linked gives more detail. Buying up a rank is definitely a possibility in the lower dahns, but political appointments, military promotions and such seem to be a big part of it too.

It's actually not really clear to me how the system works for the middle levels (low dahn lighteyes and high to mid nahn darkeyes) live since our major characters tend to be either nobility/royalty or bridgemen/slaves. I kind of get the feeling from comments about "tenners", the possibility of Kaladin marrying up discussed in his flashbacks, Hesina having lighteyed ancestry, etc. that the social stratification for many if not most people isn't as strict as our main viewpoint characters imply. That WOB also implies the same; Brandon says that it's easier to move between ranks than the historical British or Indian class systems.

On the other hand there's also a WoB where Brandon says most of the characters would really be more prejudiced than he lets come out in the books since it would be off-putting to readers. So I'm not really sure how to reconcile those ideas...

Unless maybe the possibility of mobility (in theory even from darkeye to lighteyed, through winning a Shardblade) creates 'justification' for looking down on the lower levels of society?