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This question is related to the world from my prior questions, in which several types of intelligent hominids evolved in isolation, until they were rediscovered, conquered, and bred into a biological caste system by a dominant species.

BACKGROUND

Domesticated animals often have patches of white fur. My dog, for example, has a near perfect star shape right in the center of her chest. This got me thinking about something on different lines:

I'd like it if my noble caste could breed their house servants to have heritable crests. The resulting lineages would then be associated the with other real and imaginary attributes, giving my nobles a jumping off point to trade, sell, and argue obsessively over superior bloodlines and purer stock. Edit: I should make explicit that I would like this to be at least partially delusion on their part; aside from the obvious marker and a few minor physical traits, I'd like mental differences between crest lines to have more social than biological reality.

QUESTION

  • Could you breed a hominid to give it a heritable mark, such as a patch of discolored skin or hair, that makes a simple but clean and coherent shape? Edit: Preferably on the chest or forehead. The servants would otherwise be physically distinct, but more like human families than dog breeds.

If the above premise holds I'd also like to know what would happen if you crossed the line of a crested hominid with one bearing a different crest, or no crest at all? Finally, to select for a trait this finely would the breeders require special knowledge of, say, Mendellian genetics or the like? Or could they just apply the methods humans have used since time out of mind?

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    $\begingroup$ You want "stars upon thars" and not just red-heads or blue-eyes? $\endgroup$ – user25818 Jan 5 '18 at 20:37
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    $\begingroup$ Crests as male chicken have or heraldic badges like noble families use? Or just any identifying physical attribute, e.g., the famous Habsburg lip? (BTW, a heraldic crest is a minor component of an achievement; the most important component of a heraldic achievement is the coat of arms displayed on the escutcheon) $\endgroup$ – AlexP Jan 5 '18 at 20:43
  • $\begingroup$ @AlexP Heraldry is a good comparison, in that I'm looking for a mark in a definite shape to distinguish bloodlines. The heritable royal birth mark trope is also comparable. Ideally, they'd have a patch of discolored or even raised skin on the chest or forehead, forming a relatively simple shape like a star, a sword, bull's horns, etc. $\endgroup$ – Random Jan 5 '18 at 20:49
  • $\begingroup$ @notstoreboughtdirt: Exactly, but heritable. My nobles need to establish the breed purity their sneetches. D: $\endgroup$ – Random Jan 5 '18 at 20:58
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    $\begingroup$ Ah, you mean how to create a new breed of domestic animals? You do realize that for the breed to breed true all matings must be within the breed? For example, blond hair and blue eyes are heritable in humans, and, in places such as France, Spain or Italy, they were much more common among nobility than among commoners. But as soon as a yellow-haired blue-eyed nobleperson breeds with a dark-haired black-eyed commoner all bets are off regarding the hair and eye color of the descendants. $\endgroup$ – AlexP Jan 5 '18 at 20:59
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Piebald patterns in a wide variety of mammals, like cats, horses, and mice create white spots of certain patterns that override whatever skin and hair color the animal would otherwise have.

Cats are bred for specific patterns (tuxedo, mitted, mask and mantle, etc.). Horses have fewer variations, but the same general genetic white out pattern that overrides the coat pattern.

These patterns can be created by breeding, with breeders seeking out random mutations to diversify patterns, like tulip or snake breeders that have made rare colors common.

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    $\begingroup$ People have cross-bred Maine Coons to bring the breed's mane to the second breed. People have bred horses for centuries for strength, agility, color, stamina, and height. The Nazis wanted everyone to be blonde with blue eyes (and he wasn't the first to tamper with eugenics). We breed plants for food value, color, disease resistance, etc. Frankly, human history is filled with the effort to breed specific attributes into almost everything. $\endgroup$ – JBH Jan 6 '18 at 0:13
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Well - Mandrills are a good precedent. Technically they're monkeys, not hominids, but that's close enough for a lot of medical and other biological purposes. See Link (https://en.wikipedia.org/wiki/Mandrill).

To see how far you can take things with selective breeding, compare a chihuahua, a great dane, and the asian red wolf. All the same species, just bred for particular characteristics.

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Depends how specific you're talking about. If you want something like, say, "a large brown mark on the center of the chest", as far as I know there's no way to ensure that. Often the placement of such markings isn't even genetic - if you cloned an orange-and-white cat, their clone would be orange-and-white, but the positioning of their orange patches would be completely different, just like how identical twins have different fingerprints.

However, if it would work to just have one strain have purplish marks while another has brown marks or something like that, that's readily doable.

Possible genetic bases for distinctive markings for humans:

Port-Wine Stains - reddish or purplish birthmarks caused by a vascular anomaly, usually located somewhere on the head or neck. Can be the result of certain genetic syndromes, but non-syndromic port-wine stains have been linked to mutations in the GNAQ gene(1). These mutations have only been reported in heterozygous form, so it's uncertain what impact they'd have if homozygous, but Basset Hounds' short-limbed dwarfism mutation is homozygous lethal and that hasn't stopped humans from turning it into the basis for a domesticated breed. If homozygous GNAQ is lethal, they'd have to have individuals with and without port-wine stains in the same families, but might be more inclined to actively show off the ones with the birthmark.

Freckles - Small brown dots on the skin that form in response to sunlight exposure, freckles are associated with polymorphisms in the MC1R gene (2). The same alleles that cause freckles also tend to cause lighter skin tone and reddish hair. Freckles are associated with slightly higher risk of melanoma, but not a serious cause for concern. These polymorphisms are commonly seen in homozygous form, and are especially common in certain ethnic groups such as Celtic people.

Waardenburg Syndrome - Waardenburg Syndrome is associated with a distinctive facial appearance, patchy depigmentation in hair, eyes and/or skin, going grey early, and deafness. It's caused by MITF mutation. In heterozygotes, it can often result in no impairment in hearing, just an unusual appearance, but homozygotes have more severe symptoms(2). Still, you could conceivably have a noble house who is fine with having deaf servants breed them to be homozygous for one of the less severe mutations that causes Waardenburg Syndrome. They'd probably issue commands using sign language, and might have the bonus of being less likely to have servants passing information to their enemies. (Some slaves historically had their tongues removed for a similar purpose.)

There are many other potential genetic variations associated with distinctive pigmentary variations, far too many to list here. Some cause other symptoms, but anything that doesn't stop them being put to work or that only affects a minority of individuals wouldn't necessarily rule them out. After all, plenty of domestic animal breeds have been selected for features that cause impairments in their natural functioning, such as short nose syndrome in dogs or even the polled (no horns) trait in cattle (while cattle owners often prefer cattle without horns and will remove horns on breeds that grow them, in the wild cattle without horns would be at a serious disadvantage).

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4508108/
  2. https://www.nature.com/articles/jhg201296
  3. https://onlinelibrary.wiley.com/doi/abs/10.1002/ajmg.a.60693
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