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Domesticated
Evolution In A Man-Made World
Richard Francis
All 'small' (under 25 lbs) dogs have the same point mutation which affects a gene that codes for a growth factor called IGFI. This commonality even though different small dogs come from different branches of dog family (ie the smallness bred in later, often just in last 150 years), which means that the potential was there in original wolf genotype (but always bred out in the wild, for obvious reasons).
Three different genes alter coats of dogs - long hair, furnishings (setter feathers or face hair of bearded collies) and curly hair. All wolves are short haired ('smooth coated') so these changes must be due to later mutations.
Wolves vary in colour from near white to dark gray, but dogs have added the yellow-red-brown palette, plus black, plus piebald spots, none of which occur in wild.
We have interfered with the skeleton. Wolves hold their tails out straight, but even the most wolf-like dogs (huskies or malamutes) have up-curled tails, which are never found in wolves. Other breeds, such as German shepherds, the tail is always down.
And major behavioural differences - wolves never bark. They can't read your intentions as a dog can - can't follow your gaze, doesn't respond to your emotions or seek your approval, even if raised from birth by humans. A wolf will "understand" you as much as a cat will, which is to say, not at all. Our ability to train dogs rests on their acceptance of our dominance. Wolves simply never see things that way, even when hand-reared.
So how did dogs come to be like that? Was each trait selected independently, or did they come as a package. Russian researcher Dmitry Belyaev thought it was a package deal, and he believed it was behaviour (tameness) that was selected for, and that everything else came along as a consequence.
To test the idea, Belyaev set out to experimentally replicate the domestication process with foxes from a fur farm in Estonia. 30 males and 100 females were chosen from thousands of foxes at the farm, on the basis of ability to tolerate human proximity without fear or aggression. Only 5 per cent of the tamest males and 20 per cent of the tamest females were allowed to breed in each generation, and all were raised with minimal human contact to avoid trained as opposed to evolved behaviours.
By the 4th generation, some pups began to wag their tails when near their caretakers - an unprecedented behaviour for foxes. By the 6th generation pups were whining and licking human's faces as dogs do. The tail-wagging, face-licking foxes were labelled 'elite'. The proportion of these increased with each generation, and by the 30th, had reached 49%. By the 40th, they all were elite, and could be adopted out as pets.
And, they had become dog-like in being able to recognize human gestures or gaze.
But as well as the behavioural changes, physical ones. Piebald markings, particularly the distinctive white blaze we see on horses and cattle as well. Floppy ears and curled tails. Leg bones and snout shortened.
All animals have a socialization window. Once it closes, they can't be tamed/domesticated. Tamed foxes had a retarded development of stress hormone which normally makes adult foxes suspicious and aggressive. And the ability to interpret human gestures may simply indicate a persistence of the juvenile trait of paying attention and imitating what mother does.
Belyaev confirmed his idea that evolution responds particularly to environmental stress. When something destabilizes local environment, the phenotype gets heavily selected for whatever is best suited to the new conditions. The more radical the change, the fewer the survivors, and the greater preponderence of what were outliers before.
In the case of B's foxes, it needed no new mutation; they simply exposed latent traits by selecting for tameness.
Foxes are solitary, wolves are pack animals and since adapted for a hierachical system, should be easier for humans to insert themselves, making Belyaev's achievement even more noteworthy. Also noteworthy is the way the fox -> fox-dog transition parallels the wolf -> wolf-dog transition, especially the traits that came along for the ride, like floppy ears, shorter snouts and piebald coats. But it's not only the canine family - similar things found in domesticated birds and fishes.
But the really interesting question is how much this applies to humans, given that we seem to have self-domesticated.
The genetic difference between a wolf and a pekingese is minuscule; far less than the difference between a wolf and a coyote, which much more closely resemble each other.
Dog breeds have changed evolved since C19 - one event changed everything: the 1874 founding of the first kennel club, in London. Ostensibly to maintain breed standards, but, by promoting competitive dog shows, they wound up encouraging rapid breed divergence.
And the rapid breeding, which included a lot of in-breeding (ie fathers mated with daughters) to encourage desired characteristics, meant a rapid accumulation of genetic defects. Which is why pure-bred dogs have a much shorter lifespan than mongrels, and why dogs are an exception to the mammalian rule than the larger species live longer than smaller ones. Elephants live longer than cats which live longer than mice etc. But large breeds like Great Danes live only 6-8 years, while toy breeds can live up to 20 years.
Around humans, the boldest feral is shyer than the shyest domestic cat. As with foxes, there is a window of socialization, and it seems to close earlier with cats than with dogs. But even domestic cats more closely resemble their wild ancestors than do the most wolf-like dog breeds.
Teeth give impt clues. All carnivores have scissor-like shearing teeth (carnassilas) for meat. Bears, with a largely vegetarian diet, have small carnissials and large (grinding) molars. In dogs, both are large, reflecting their omnivorous diet. Cats have only tiny molars; their teeth are so specialized that they cannot chew.
Sonic hedgehog is a master developmental regulatory gene that forms a gradient concentration. The effect of this on the developing embryo depends on concentration levels. For example, polydactyl cats wind up with too many toes because of too much sonic hedgehog
Other wild animals, such as raccoons and foxes, are beginning to self-domesticate, to take advantage of the food humans leave lying around. First step is moving from solitary to social groups, so have to evolve tolerance of fellows, which they don't have in the wild unless food is plentiful.
This tolerance, both of peers and human proximity, simply reflects stress hormone levels. The least stressed were healthier, and were able to spend more time catching food than worrying about neighbours.
Raccoons introduced to Europe and Japan as a result of a cartoon series Rascal the Raccoon which induced impressionable kids to beg their parents for baby raccoons as pets. Unfortunately they all grow into surly adults and get tipped out to fend for themselves. In some German and Japanese cities, they are now at American population levels.
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Domesticated animals losing genetic diversity - in Holstein cows, 2 bulls, father and son, are responsible for 7% of the genomes of the entire American herd.
Jewish rites - on Yon Kippur (The day of Atonement), an ox and 2 goats were selected for sacrifice. The ox died for the sins of the High Priest and one of the goats died for the sins of the community. The second goat - the scapegoat - was exiled into the wilderness to pay for the whole community's sins. Lest it return and reinstall the community's sins, someone would be dispatched to discretely push it over a cliff.
But Christians demonised the goat. The famous passage in Matthew where Christ says the sheep will be separated from the goats - the sheep to join the heavenly flock; the goats to join Satan, the evil goatherd. Apparently the high incidence of homosexuality among sheep (at least 8% of rams) doesn't count against them.
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Easy to understand why - sheep are far more docile and tractable. Goats are far more individualistic and are not natural followers. Goats are far more curious and playful. And they're smarter - in bad weather they'll find the nearest shelter, whereas sheep will just clump up, and often freeze together.
And goat milk is better for humans - much more like human milk than cow milk, and so more nutritious. And lower in lactose than cow milk. Yet little has been done to improve natural yields of milk or meat.
Equids - horses and zebras - have less efficient digestive system than ruminants like cows or wildebeests. So zebra manure textured with undigested grass while ruminants leave liquid pats. But equids faster digestion means they can survive on poorer pastures.
Horses have a gene for producing myostatin, which is significant in muscle development. It has 2 alleles. One, the 'e' allele, promotes endurance, the other, 's' faster over shorter distances. All wild horses, and until about 1950, almost all thoroughbreds, were 'ee'. Then a stallion Nearctic inherited 2 copies of 's', was mated to a 'es' mare, and produced in 1961 Northern Dancer, who became one of the most influential sires of modern times. There ensued a 'genetic sweep' where the frequency of the 's' variant rapidly spread through the population.
For a long time, S America isolated, and marsupial mammals thrived. When primates and ancestors of rodents such a cavies arrived, there were no carnivores or large herbivores. With so many ecological niches unexploited, the cavies diverged spectacularly. Some became huge - one species the size of an auroch, another the size of a bison.
Lab mice have gone soft. In mice, muscle strength is measured by how long they can hang from a dangling cord. Lab mice can do that for 30-40 seconds. Wild mice just pull themselves up, climb to the top of the cord and piss off.
Alongside his fox expt Belyaev tried brown rats. Although started much later, the shorter maturity meant there have been far more generations. Again selected for tameness and again associated traits came along for the ride - lower anxiety, earlier sexual maturity, year round fertility, wider range coat colours.
Suggestion that bonobos have self-selected for tameness, perhaps based on female solidarity (which is itself based on unprecedented levels of lesbian sex). Both chimps and bonobos are equally sociable and non-aggressive. But as they age, chimps get increasingly intolerant and aggressive, while bonobos retain their juvenile levels.
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