Pearl: a Palomino Complication

Sorry, I do not have a single photo of a pearl–just haven’t been able to find one. Sponenberg doesn’t, either. You’ll have to go with the descriptions.

Last week we discussed palomino as if there were just two forms of the gene associated with palomino color: cream and non-cream. The whole story is a little more complex, but I’ll have to introduce some genetic terminology to explain it, even though I’ve used the terminology, without explaining it properly, several times already.

The three new words we’ll be using are locus, allele and wild–type.

Locus means place in Latin, and it originally meant a place on a chromosome. Since genes code for proteins and are now known to be a little more complex than just the place on the chromosome, it now means the particular protein coded for.

There can be slightly different forms of a protein having the same function, and the different stretches of DNA (genes) that code for these slightly different forms are called alleles. Using this terminology, every horse has two alleles, one from each parent, at each locus (plural loci.) Last week we discussed two alleles, cream and non-cream, at the cream (C) locus.

The complications come from the fact that there are in fact three rather than just two alleles at the cream locus. Each individual horse can have any two of these three alleles. To avoid confusion, I am also going to introduce the term wild-type for the gene assumed to be the “normal” allele at a locus in the wild ancestor of a domesticated animal. What we called “non-cream” last week is in fact the wild-type gene that gives normal full color.

(Note that the wild ancestor of the horse is not the “wild” horse of the West—these are in fact feral, descended from domesticated stock. The only true wild horse alive today is Przewalski’s horse in Asia. The Tarpan in Europe was also wild, but became extinct in the 19^th century.)

Using our new terminology, the cream locus has three alleles: wild-type, cream, and pearl. Pearl was recognized quite recently, and it has a very low frequency except in a few Spanish and Portugese breeds and their derivatives. It could be considered a weaker allele than cream, as it has less diluting effect on the coat.

A horse with one wild-type allele and one pearl allele will look very much like a wild-type horse—chestnut, bay or black depending on what genes are present at other loci. A very close look will show skin slightly lighter than normal, or with small pale spots.

A horse with two pearl alleles will have the red pigment diluted only slightly more than would be expected for a horse with one cream allele and one wild-type allele. Black pigment, however, will be diluted much more than is the usual case for a horse with one cream and one wild-type allele. Thus a bay with two pearl alleles at the cream locus dilutes to tan or gold on the body with chocolate mane, tail and lower legs. A chestnut becomes virtually identical to a pumpkin-skinned palomino (technically gold champagne.) And a black becomes a grayish tan with chocolate mane, tail and lower legs. All of these colors appear very similar to those produced by a single dose of the champagne gene, which is a completely different gene at a different locus, but give very different breeding results. Luckily there is a DNA test for pearl.

If a horse has one pearl allele and one cream allele, the resulting color will be cream, usually slightly darker than the cream resulting from two cream alleles (cremillo, perlino or smoky cream.) In particular the eyes are generally blue or amber, and darker than those of cream horses with two cream alleles.

As I mentioned before, there are a number of different ways of diluting horse color, and when two or more at different loci are combined some very odd colors can result and it may not even be possible to tell what genes are present—or what colors can be produced—without DNA testing.

Next week I’ll consider linebacked dun—one of the few horse genes where the wild-type allele is rare today in many breeds.

(If anyone has photos I could use to illustrate some of these horse coat colors, I would really appreciate them.)

Palomino (Cream) Genetics

Sometimes scientists get it wrong. With time other scientists generally catch and correct the errors, but the initial efforts to explain the palomino color were wrong on two counts: first, the assignment of palomino dilution to the albino locus C (for color,now known to be the gene that codes for the enzyme tyrosinase) and second, the assumption that all dilute colors were palomino. We now know both are false, but the early investigators did explain why palomino does not and cannot breed true.

Palomino. A bay and another palomino are in the background.

A palomino is, ideally, a horse the color of a new-minted gold coin with a white mane and tail. At one time, breeders tried to get them to breed true, and there are still breed registries based on palomino color. But two dark-skinned palominos, mated together, will produce only about half palomino foals, and many of them will not be the pure gold with white manes and tails wanted. Why?

Palomino is an example of what is sometimes called over-dominance or partial dominance. The color is due to a dilution gene, cream or cremillo, acting on a chestnut background. The locus is still called C, with primary alleles C⁺ and C^Cr. A single dose of cream will dilute red pigment to golden yellow, while having very little effect on black pigment—thus the dark skin. A double dose will further dilute the red to a pale cream hard to tell from white, and black to a shade that varies from a slightly dirty white to pale gray.

Palomino with a Bend Or spot on the neck, far more conspicuous on a palomino than it would be on a chestnut.

All horses, in fact all mammals, have two copies of each gene, one from the father and the other from the mother. If the basic color of the horse is chestnut and the horse has a cream gene from one parent and a non-cream gene from the other, the result will be a palomino. If one parent is a cremillo (the result of a double dose of cream acting on chestnut) and the other is chestnut all of their foals will be palomino. But if both parents are palominos, about a quarter of their foals will get the non-cream gene from both parents and will be chestnut, a quarter will get the cream gene from both parents and will be cremillos, and half will get one of each kind of gene and be palominos.

Cremillos are popular with some horse owners today, but at one time they were considered very undesirable by palomino breeders. They have pink skins and blue eyes, and they may be more subject to sunburn than horses with dark skin and eyes. They are not, however, albinos or due to any form of the albino gene. The cream gene has been found and sequenced, and a DNA test for cream is available.

Palominos don’t necessarily have a clear gold body color, or white manes and tails. Remember chestnuts have varying amounts of black hair sprinkled through the coat, and these black hairs will remain and become even more conspicuous if the red of the coat is lightened to gold. Some chestnuts even have what are called Bend Or spots, areas much darker than the body, or even black. These will be much more conspicuous with  the C⁺  C^Cr combination..

Further, chestnuts often have manes that are self-colored or even darker than their bodies. These characteristics will carry over into the dilute animals, and it is not unusual to find palominos with considerable black shading or dappling, and black hair mixed into their manes and tails.

What happens if the cream gene is combined with a base color other than chestnut?

The effect of a single does of cream dilution on a bay, giving buckskin. There is considerable confusion between buckskin and dun, but this horse has the palomino or cream dilution.

One dose of cream on bay gives a buckskin, with a yellow body and black mane, tail, and lower legs. A double dose of cream gives a perlino, a cream horse with mane, tail and lower legs very slightly darker than the body, blue eyes and pink skin.

A single dose of cream on black may be missed entirely, and the horse just called black. Some blacks with a single dose of cream are slightly lighter than normal, and are called smoky. With a double dose of the cream gene, a black becomes a smoky cream, again with blue eyes and pink skin.

Although the darkest variants of cremillo, perlino and smoky cream can be distinguished from each other, the lighter variants are very difficult to tell apart. Often they are just called cream, the distinction becoming important only if they are bred.

A base color of brown or very deeply black-tipped bay? I saw one once in winter coat, and at first glance he looked like a blue roan. Looking closely, however, he did not have a mixture of black and white hairs; rather each hair had a cream base and a black tip. I was able to recognize the same horse in summer coat only because a stable employee pointed him out. In summer coat he was a typical seal brown.

I emphasized palominos with black skin because it turns out that gold horses with lighter skin (sometimes called pumpkin skin) are due to a completely different gene, champagne. I’ll talk about this later.

If you want to read some very basic information about genetics, especially genetics of coat color, have a look at http://bowlingsite.mcf.com/Genetics/Genetics.html

The Agouti and Extension loci in Horses

This was originally posted on November 27, 2010 with different photos and no comparison with other animals. Since I now have far more photographs, I have decided to re-post some of the old horse color genetics posts with better photos.

Blood bay with star

The base colors of horses are bay, black and chestnut, possibly with the addition of wild bay and seal brown (tan-point.) These colors are distinguished by where red and black pigment are found, both where on the whole horse and where on individual hairs. I’m going to go into more detail this time on what determines these base colors.

Red pigment in horses (more correctly, phaeomelanin) can appear brownish red to copper, sometimes approaching gold, in the absence of dilution factors. With dilution factors, it can include white, cream, tan, yellow and gold shades.

Black pigment (more correctly, eumelanin) is black in the absence of modifying genes. In horses, the genes that dilute black to blue-gray or black to chocolate brown are not known to occur, though they do occur in other species. Chocolate Labradors, for instance, have the gene that dilutes black to brown, but this is very rare, if it occurs at all, in horses. Some dilution genes in horses do affect black, changing it to shades from bluish to sepia to dirty white or even nearly pure white.

The Agouti locus is known in almost all mammals. It codes for a protein that affects more than coat color, and is complex to sequence. In general, however, more red pigment is dominant to more black pigment.

The Agouti locus is given the symbol A. Agouti alleles are A with a superscript showing the particular form of the allele. Thus A^a is the symbol for recessive black, also called non-agouti. A^t stands for seal brown (black with tan on the inner legs, flanks and muzzle, very hard to tell from black with the mealy gene) which is also called tan-point in some mammals. A^A is the symbol for bay. A⁺ is the so-called wild bay, where some red pigment appears on the lower legs. Note that + is always the symbol for the “wild-type” allele, that which is believed to be the predominant gene in a truly wild or ancestral population. The wild-type allele can be very rare in a domesticated population if it has been selected against.

Every horse has two alleles at each locus. If one allele is dominant to the other at the agouti locus, that is the allele that determines the color of the horse—if the extension locus allows it to. The order of dominance at the agouti locus is wild bay is dominant to all others, bay is dominant to black and tan-point but recessive to wild bay, tan-point is dominant to black but recessive to both bays, and black is recessive to the other three alleles. This means that two recessive blacks can produce only black foals, while two wild bays can produce any color they carry the genes for.

This horse could be a seal brown or a very darkly shaded bay.

The agouti gene, by the way, was named for a South American rodent, the agouti. It was originally defined as controlling banded hair, seen in many wild animals. In fact, banded hair (black tips on red hairs) can be found on most bay horses, though you’ll need a magnifying glass and very good light to find it. Many of the darker shaded bays actually have rather deep black tips on individual hairs. In a few extreme cases, only the tips are visible in summer coat, and a bay horse may appear to be a seal brown (black with tan shading on muzzle and flanks) in summer and a definite dark bay in winter. The horse in the photograph is probably of this type.

Sable and white Shetland Sheepdog–genetically Agouti.

Agouti in horses is bay. In dogs the same genetic color is sable, and in mice the standard gray color. (The yellow is very light.)

The Extension locus is given the symbol E. Again, this locus is very widespread in mammals. The wild-type allele, E⁺, allows the agouti alleles to be expressed. There is also a recessive allele, E^e, which suppresses the black pigment. Not completely—a horse with two E^e alleles can still have black whiskers and may have black hairs scattered throughout the coat. (In contrast, an E^eE^e dog has no black in the coat or whiskers, but an E^eE^e fox will be a typical “red fox” color.) But it will not have the black mane, tail and lower legs of a bay. In fact, an E^eE^e horse will be a chestnut, regardless of what may be at the Agouti locus.

E may also have two alleles dominant to the wild-type allele. These are dominant black E^D and countershading, E^B. (I have to say I have my doubts about countershading, though countershading on bays is well established.)

At the E locus, alleles with more black are dominant to alleles with more red. Further, the E locus can hide what is present at the A locus. An E^D horse will be black regardless of what alleles are present at the A locus, and an E^eE^e horse will be chestnut regardless of what is present at the A locus. The word epistatic is sometimes used to define this relationship between loci—Extension is epistatic to Agouti.

Note that I am following Sponenberg, Equine Color Genetics Third Edition, plus my own observations on hair color.

The Basic Colors of Horses

One of the lighter shades of chestnut, with flaxen mane and tail. This horse almost overlaps the darker shades of palomino, but it is a chestnut.

This is a repeat of a post originally dated October 2010. Because I now have far more photographs of horses than I had at that time, and because the horse color genetics series has been so popular, I am reissuing it with more photographs.

I got a new book two years ago: Equine Color Genetics third edition, by Philllip Spoenenberg. I already had the first two editions–and how things have changed since the first edition came out! Even the second edition had only four types of dilution genes. Now there are six, with at least one more that has not been located yet.

A more typical shade of chestnut, with a flaxen mane and self tail.

Lineback duns and creams were clearly separate by the second edition, which also greatly expanded on silver dapple and added champagne. But the third edition added pearl, mushroom and a rare dilution, probably recessive, found in Arabians.

Before starting to look at the effects of the dilution genes, not to mention the other genes that affect horse color, it is important to realize that horses, like most mammals, have two kinds of

A fast glance might misidentify this horse as a bay but the mane and tail, while darker than the body, have red as well as black hairs and the lower legs lighten toward the hooves.

pigment. One, eumelanin, is black, and while some of  the dilution genes may affect it, the kind of brown that produces the chocolate Labrador is not known to occur in horses. The other pigment, called phaeomelanin, varies from rich red-brown to a lighter golden red which can be confused with palomino. We’ll call that red, but that color can also be changed by other genes.

The three basic horse colors are chestnut, bay, and black. (Seal brown may be a fourth color genetically, but that is still under investigation.) Patterns of white,

A very dark shade of chestnut, sometimes called liver chestnut. A magnifying lens would show that the darkness of color is not due to the red/yellow phaeomalanin, but to interspersed black (eumelanin) hairs. The darkness of mane and tail are likewise due to interspersed black hairs, but the legs clearly lighten toward the hooves. The two horses in the background are more typical chestnuts.

interspersed white hairs, or dilution may act on any of these colors, as may a general scattering of black hairs through the coat. But these three colors are the base for all horse colors. DNA tests are now available for the genes that produce all of these colors.

Chestnut is predominantly red, including mane, tail and lower legs. The mane and tail may be lighter than the body (often called flaxen, and sometimes with interspersed white hairs) or darker than the body (usually due to interspersed black hairs.) The dark shades of chestnut, called liver chestnut, often have interspersed black hairs over the entire body.

Chestnut is due to a recessive form of the same gene, called extension, that produces yellow Labrador Retrievers. Chestnut is recessive to normal extension (which allows black mane and tail) but in contrast to dogs, black can occur in the coat. Recessive means that chestnut to chestnut breedings can produce only chestnut foals, but bay to bay (or bay to black or black to black) can produce chestnut.

Typical bay, cantering. Any shade of phaeomelanin found in chestnut can also be found in bay, but the black mane, tail and lower legs are diagnostic.

Bay horses have red on the body, but the mane, tail and lower legs are black. Interspersed black hairs are again a possibility. In addition, many bay horses have some body hairs (most numerous on the upper part of the horse) which have red bases but black tips. This type of hair, with a band of red on a hair with black tips (and sometimes even black bases) is very common in mammals, and is called agouti. Bay is in fact an agouti gene. and is dominant to non-agouti.

Black horse with star and snip. The owner thinks this horse could be a brown, but it is not uncommon for black horses to sunbleach slightly in summer, in which case they may appear to have brown in their coat.

Black is most commonly due to non-agouti. Black horses have primarily black hair. There is a separate gene, called mealy, that can produce lighter shading on the muzzle, though there is some evidence that a similar effect can result from an agouti gene called tan-point. Black is usually recessive to bay–that is, two bay parents can have a black foal, but it would be very unusual (and probably an indicator of the rare dominant black) for two black parents to have a bay foal.

Any of these colors may have white markings, and as long as the markings are confined to face and lower legs, the horses will still be called chestnut, bay or black. A bay, for instance, can have four white stockings and still be a bay. Only the most extreme white markings can hide which base color is present.

I’ll be blogging on more of the horse color genes in the next few weeks. If you want a primer on basic genetics, check out my website on coat color genetics in dogs.

Off to the Shows!

Every year the Tanana Valley Kennel Club holds 3 days of dog shows and obedience trials over the Memorial Day weekend. I used to participate in both breed and obedience. (In tracking, too, but that’s a different weekend.) Sadly, I was already too unbalanced (physically) to participate by the time the AKC added agility, herding, and rally obedience, but I still enjoy watching and fantasizing about what some of my Shelties could have done if those activities had been available back when.

I still attend, to catch up on old friendships and watch the dogs. Here are a few of the things I saw—mostly this year, though I’ve included one shot from past years to show the Chinese Crested.

This Papillion won Rally Advanced B, which included heeling off lead between a dish of bacon treats and a toy.

Harlequin and mantle Great Danes. Cropped and uncropped ears are now equally acceptable (at least in theory.)

A Wirehaired Pointing Griffon, not a common breed.

A blue merle Sheltie , ring ready, with ringside activity in the background.

Most of the exhibitors camped out on the fairgrounds, with a wide assortment of campers and tents.

The first day’s group second, chilling out after ring time. Exercise pens are common in the camping area.

Not a breed adapted to Alaska!. This Chinese Crested is not shaved; the breed has hair only on the head, legs and tail. The spotted skin is actually not uncommon in some white dogs.

A pair of Whippets outside the show building

Jarn’s Journal Year 2, Day 355

Year 2, Day 355

Fifteen days it took them to get Meerkat to the place where Storm Cloud’s group was encamped, and by that time most of Storm Cloud’s group had moved on. They’d left a few behind, and everyone seemed to know where they were going, so I didn’t worry too much about leaving them at the old camp site. Lion’s group had reached good grazing and water several days earlier. Everyone was feeding themselves and finding water,  so all I had to do was continue to have Patches track Storm Cloud’s group to the Gather.

The Gather. Patches. Two problems for me to worry about. Do I really want to go to their Gather? Should I, or have I interfered more than enough already? And what am I to do about Patches? How easily the impulse to help can lead us into trouble!

I could have ignored the orphaned and starving puppy. Then I would not be agonizing over the moral problem of just how far I can justify meddling with Patches’ mind. She is not a domesticate, whose mind is adjusted to living with a dominant species. She is a tamed wild animal, and her instincts are telling her she should be part of a pack, challenging the dominant female for the right to breed. But she understands nothing of pack living.

I could free her, easily enough, but she could never survive on her own. No pack would accept her. Any dominant female would kill her on sight. She knows nothing of fighting; I myself have conditioned her against the very things that might keep her alive.

True, she is not a sentient, a creature that is aware of its own mortality, I can modify her mind, deepen her acceptance of humans as her pack, even reduce the instinct to mate. Perhaps that is what I should do? I cannot think of anything else. Perhaps I should not have saved her, but would I myself be alive if I had not?

In case you’re new to Jarn’s Journal it is a Friday feature of this blog, and represents the (fictional) journal of a (fictional) human-like alien stranded in Africa 125,000 years ago. The journal to date is on my author site, and is the remote back story of the setting of my science fiction books.

The Essential Dinosaur Pack Disc 2: DVD Review

This disc, although it has a copyright date of 2008, is a collection of TV programs originally aired between 2003 and 2008. Thus none are really up to date.

“The Mystery Dinosaur,” from 2006, deals with the discovery of  “Jane.” This fossil has been variously identified as a Nanotyrannus and a juvenile Tyrannosaurus Rex. The program is primarily about the argument, which could date it, but as far as I can tell, the argument has never been resolved. Thus the program is still fairly current, though it is more science than entertainment.

“Dinosaurs: Return to Life” deals with the observations that the differences between dinosaurs and birds appear to be due to a relatively small number of mutations. Could birds be “reverse bioengineered” to produce something like dinosaurs? Would we really want to?

The four-program series “Dinosaur Planet” first aired in 2003, and unlike the rest of the programs in this set, it is definitely intended to be entertainment. Each of the four episodes focuses on one or two individual dinosaurs and follows them through a period of their lives. Each episode also covers something that is important or intriguing in the fossil record, and links back to that record. Thus “White Tip’s Journey,” featuring a Velociraptor,  suggests one explanation for the famed (real) fossil of a Velociraptor locked in a death struggle with a Protoceratops.

“Alpha’s Egg,” featuring the large sauropod Saltasaurus and the medium-sized predator Aucasaurus,  is based on the discovery of  a Saltasaurus nesting ground,  fossilized in Patagonia.

Pod of “Pod’s Travels” is based on a Pyroraptor,  a European raptor genus. The episode includes the natural hazards (earthquake, tsunami) that made occasional travel between the islands that made up Europe 80 million years ago possible. The focus of the program is on the dwarfing effect that islands tend to have on species. Pod is a Gulliver among Lilliputians when a tidal wave sweeps him to a much smaller island.

“Little Das’ Hunt” follows a juvenile Daspletosaurus  (an earlier close relative of Tyrannosaurus Rex) learning to hunt, and a herd of Maiasaura. The episode is based on a group of Daspletosaurus and Maiasaura found fossilized together in Montana, but the evidence for the kind of pack behavior shown in the episode is scanty and controversial.

Obviously there is a good deal of imagination going into the behavior, color, feathers or lack of them, musculature and behavior of all of these dinosaurs. Here I want to mention three, because they struck me so strongly.

The first is the underline of the creatures portrayed.  Theropod dinosaurs did indeed have a bone jutting back from the pelvis. However, the velociraptors are shown as having this bone stick out of the body, covered by a narrow wedge of tissue. It seems to me that this arrangement would be very susceptible to breakage, and that evolution would have reduced the length of the bone fairly fast. It makes much more sense that the tail and the posterior part of the belly were much deeper, with the projection buried in muscle. In fact a mummified hadrosaur had exactly this conformation, with a tail much deeper than anyone expected. Why not Velociraptor?

Second is the behavior of prey dinosaurs. Granted they didn’t have much brain, but instinct is also guided by evolution. Threatening a predator with teeth adapted to munching relatively soft leaves, and exposing the vulnerable neck in the process, does not make sense. Kicking (recent work has shown sauropods had vicious kicks) or tail swipes are far more reasonable for the big plant-eaters. This bothered me as far back as the Disney dinosaurs in Fantasia, when the stegosaurus turns to try to threaten T. Rex with its tiny mouth, instead of lashing out with its spiked tail. Now Disney may be forgiven – after all, Fantasia came out in 1940. Between making his dinosaurs animatable by artists drawing each cel by hand and the paleontological knowledge of the day, he did a respectable job even if his sauropods did have necks like snakes and his characters never actually lived at the same time. But that stegosaurus is pure theater, and Discovery Channel should have known better.

The third is grass. There is now some controversy over whether dinosaurs and grass coexisted, but the amount of grass shown is almost certainly incorrect.

Overall evaluation? Watch, but don’t believe everything you see. This DVD has a lot of creative interpretation, some of it almost certainly wrong.

Jarn’s Journal Year 2, Day 339

Year 2, Day 339

I am beginning to wonder if I may have promised more than I can deliver. At least it keeps me busy!

Yesterday morning was devoted to filling water containers, finding food (for three groups now) and checking on the woman whose name, I have finally discovered, is Meerkat. Then I teleported Patches and myself to the last camp of Lion’s group and had Patches try to track them to their next camp. Patches can move a good deal faster than they can, and they usually stop to hunt well before dark, so I caught them just as they are staring to look for a campsite. Yesterday I spotted a good site ahead of them and guided them to it. By that time, however, Patches was getting tired of tracking. Getting her to follow the hunters from Storm Cloud’s camp toward Meerkat’s took a good deal more mental control than I really like to use, and it was full dark before we found them and delivered their water.

I hoped to break up the tracking by having Patches track the hunters partway in the morning, as they leave as soon as there is any light at all. Then Patches could rest while I took food and water to Meerkat and filled the water containers for Lion’s group. Actually finding the group was as much a matter of guessing as following Patches, who by that time was sore-footed as well as rebellious. When it came to following the hunters from where they’d been around noon, she simply laid down and dared me to drive her on.

I thought that by then they might be getting close to Meerkat’s camp, as after all they had estimated two days to get there. So I teleported their supplies to the camp and then flew back along the route I though they would be using. Luckily there was a full moon tonight, so I was able to find them. Lucky also that they had estimated the time it would take them so well. And I have seen most of the trail they will be returning over, so if they tell me each day where they will camp the next night, I should be able to teleport to those sites, leaving only Lion’s group to depend on Patches’ skill as a reluctant tracker.

The Jarnian Confederation: Purpose

The Jarnian Confederation, the political structure in which I’ve set all of my science fiction writing, is neither a utopia nor a dystopia. It is a pragmatic structure which has evolved over time to govern a number of planetary systems, and its primary purposes are threefold:

1. To prevent Humans from bothering other sentient species. In my universe most space-traveling races are basically cooperative for the simple reason that in order to reach technology sufficient for interstellar travel, they must go through a stage when self-destruction is possible. Humans are an exception to this: one of the R’il’nai hybridized with early proto-humans and led his offspring back to the stars, and the R’il’nai have felt responsible for them ever since.

2. To protect Humans from one species in particular, the Maungs. The Maungs are friendly, but they are a symbiotic species and one of the symbiotes, which enters a free-living state during Maung reproduction, is capable of infecting and taking over the mind of any Human in the vicinity. The best prevention, recognized by both R’il’nai and Maungs, is separation. Luckily the Maungs prefer planets both hotter and with a higher gravity than those Humans prefer.

3. To keep Human planets from attacking each other. This is actually the hardest one.

R’il’nian-Human hybrids with a preponderance of active R’il’nian genes, known as R’il’noids, actually do most of the work, and tend to regard purposes 1 and 3 as the real reason for the Confederation, with 2 being one of the main reasons the Humans accept it.

Human planets have their own governments of many types: democracies, dictatorships, patriarchies, matriarchies, oligarchies, meritocracies, anarchy (though usually not for long with any sizable population), theocracies, and just about anything else you can come up with. The Confederation government has absolutely no voice in local affairs with one exception: any Confederation citizen has the right to emigrate to any planet which will accept that person. (This may be an empty right because of finances.) But it is also true that any Confederation planet has the right to refuse entry to any person. New planets are being terraformed and settled frequently, but companies settling desirable planets generally require a substantial premium. (Undesirable planets often have a very high death rate.)

In addition to settling interplanetary disputes, the Confederation may assist in major crises, most often novel diseases or natural disasters that affect a large portion of a planet.

Because hybrids tend to have very low fertility, they are scarce and a number of Confederation laws have been developed specifically to protect R’il’noids. Before Çeren’s time this worked very well, as all the early R’il’noids inherited the R’il’nian empathy and sense of responsibility. At the time of my stories this has fallen apart, and there are a number of R’il’noids lacking empathy entirely.

I’ll give some details of the practical side of the Confederation government later.

R’il’nian Teeth

My science fiction is based on two species, the R’il’nai and Humans, and their crossbreds, the Ril’noids, living together. One of the major differences between the two parent species is in life span. The Humans have what we would consider a normal life span. The R’il’nai, while not immortal, do not age beyond maturity. A number of my characters have been alive for millennia. Crossbreds can show either pattern.

This leads to all kinds of interesting situations in the society. How do the two species interact, for instance? How many Humans would want to marry someone who would never grow old? How does a R’il’nian act toward someone he or she knows will grow old and die while the R’il’nian is still young? This is in the background of all of my plots.

Here, however, I am addressing a different problem.

Most of the cells in our bodies are constantly turning over. I can imagine a creature that looks and acts human with a near-infinite life span, except for one thing. Teeth.

Tooth enamel wears, and unlike skin, it is not constantly replaced from within. Modern dentistry can do a lot to repair wear, but I’m having to have enamel repairs already. Young mammals are born with two sets of tooth buds, one that grows into teeth suited for the small jaw of a juvenile; the second set adult sized, and that’s it. People who lived thousands of years would wear out their teeth. How to handle the problem?

The R’il’nai would have to have an essentially infinite number of replacement teeth. When a tooth was worn out, it would be shed much as a child sheds its milk teeth, and replaced by a new tooth. How? They must have some tooth stem cells in their jaws, just as we have blood stem cells in our bone marrow. Assuming that a tooth would last for 50 or 60 years, this would mean that the R’il’nai and non-aging R’il’noids are teething roughly every two or three years. I don’t think I’ve actually mentioned that, but if a R’il’noid seems to be in a particularly bad humor, he or she may be teething.