Nevertheless, it worked \u2013 both far better, and far faster, than anybody could have expected. Within eight generations, Belyayev\u2019s fox population was regularly turning up pups that lacked their forebears\u2019 fear of humans; within 20 generations \u2013 about 25 years \u2013 the breeding program had produced a line of foxes tame enough to be kept as household pets.<\/p>\n
\u201cFor those who study evolution, this is an extraordinarily short time span,\u201d pointed out embryologist Don Newgreen and principal research fellow Jeffrey Craig, both from the Murdoch Children’s Research Institute in Melbourne, Australia, in a 2014 article<\/a> for The Conversation. \u201cBut that wasn\u2019t the most surprising result.\u201d\u00a0<\/p>\n Belyayev and his successor, Lyudmila Trut, had focused only on one trait for their experiment: tameness. A fox that demonstrated less fear and aggression was allowed to breed; one that was \u201cwilder\u201d, and less trusting of the humans, was not. And while, certainly, this characteristic became widespread among the foxes, so did a group of other, more visible ones.<\/p>\n \u201cAlthough selected only for their temperament, the later generations of silver foxes also had shorter faces, smaller teeth, soft and droopy ears, curly tails, and altered color,\u201d wrote Craig and Newgreen. They became, in short, pups.<\/p>\n If you breed for dog behavior, apparently, you get dogs.<\/p>\n Image credit: Jennifer Johnson, Darya Shepeleva, and Anna Kukekova, Journal of Neuroscience CC-by<\/p>\n But even more surprising than this collection of changes in the domesticated fox population? The fact that they were all completely expected.<\/p>\n Floppy ears are a sign of domestication<\/p>\n As a rule \u2013 and elephants notwithstanding \u2013 wild animals do not have floppy ears.<\/p>\n Pets do, though. The most obvious comparison is between wolves and dogs, but it\u2019s true for many domesticated species: for \u201ccats in China, horses in parts of Russia, sheep in Italy and elsewhere, the guinea-pig in Germany, goats and cattle in India, rabbits, pigs and dogs in all long-civilized countries,\u201d noted Charles Darwin in 1859\u2019s On the Origin of Species. \u201cThe incapacity to erect the ears is certainly in some manner the result of domestication.\u201d<\/p>\n And in fact, it\u2019s not just the ears. \u201cDomesticated animals share a fairly consistent set of differences from their wild ancestors,\u201d Newgreen and Craig pointed out: they have smaller brains on average; smaller teeth and shorter muzzles; shorter, curly tails; lighter, blotchy coats; they go into heat more often, and act more \u201cjuvenile\u201d than their wild counterparts.<\/p>\n It\u2019s such a widespread and predictable set of characteristics that it has its own name: \u201cdomestication syndrome\u201d \u2013 but precisely why it occurs was one of the longest-standing mysteries in the field of genetics. From Darwin himself up until relatively recently, theories abounded: \u201cThere is no shortage of ideas about the nature of the domestication process and its effects on various domesticated animal species and breeds,\u201d admitted biologist Adam Wilkins and his colleagues in a 2014 paper<\/a> on the phenomenon.\u00a0<\/p>\n \u201cMost of the explanations proposed, however, do not attempt to account for the full spectrum of [domestication syndrome],\u201d they wrote.<\/p>\n The confusion was clear to see: even as late as 1979, hypotheses were still out there<\/a> relying on the kinds of epigenetic arguments that had been roundly debunked half a century earlier. By the early 2000s, though \u2013 and with the evidence brought forth by the silver fox experiment \u2013 the thinking had changed somewhat: biologists thought that, probably, the floppy-ear genes and the friendly-to-humans genes all lived within the same genetic regulatory network. To change one trait, therefore, would change them all.<\/p>\n It is, on the face of it, more convincing than the arguments that preceded it \u2013 but it comes with a couple of big problems. First, the proposed network would have to be huge \u2013 big enough to cover every aspect of domestication syndrome, and certainly bigger than any other known at the time. And second, Wilkins and his team argued, it was kind of too good to be true: \u201cit posits upstream mutations (or epimutations) in the hypothesized network with dramatic, widespread effects,\u201d they wrote, \u201cbut which are not lethal.\u201d<\/p>\n \u201cThus this explanation [\u2026] postulating a single network that directly controls all the traits affected by the [domestication syndrome], is not without problems,\u201d they concluded.<\/p>\n Instead, they argued, it all came down to adrenaline \u2013 and a single, temporary structure that turns up during embryonic development.\u00a0<\/p>\n Growing tame<\/p>\n In 1868 \u2013 less than a decade after Darwin\u2019s Origin of Species \u2013 an anatomist over in Switzerland with the slightly confusing name of Wilhelm His Sr was busy making discoveries equally as revolutionary.<\/p>\n \u201cHis first described the \u2018Zwischenstrang\u2019 as a band of cells residing between the neural tube and epidermis that later migrates laterally to form the spinal ganglion,\u201d explained Weiyi Tang and Marianne Bronner, both from the California Institute of Technology\u2019s Department of Biology and Bioengineering, in 2020<\/a>. \u201cToday, this cell population is known as the neural crest.\u201d<\/p>\n Now, if you\u2019re looking for a single structure with the ability to affect systems throughout the body, this is your guy. It\u2019s been called<\/a> variously \u201cthe fourth germ layer\u201d and \u201cthe only interesting thing about vertebrates\u201d because of its impact on the clade\u2019s development, with cells from the neural crest ultimately ending up in systems as diverse as cartilage, connective tissue, pigment cells, peripheral nervous system cells, hormonal glands, and more.<\/p>\n If all that sounds familiar, it should. Mess with the neural crest, and it\u2019s theoretically possible to affect not just an animal\u2019s facial skeletal and connective tissue \u2013 giving them, for example, smaller teeth, a curly tail, and floppy ears \u2013 but also its coloring, its brain development, and its adrenaline response. In short, all the traits that mark a species as \u201cdomesticated\u201d rather than wild.<\/p>\n Of course, these changes wouldn\u2019t have happened organically. \u201cWhen humans bred these animals for tameness, they may have inadvertently selected those with mild neural crest deficits, resulting in smaller or slow-maturing adrenal glands,\u201d explained Wilkins back in 2014<\/a>. \u201cSo, these animals were less fearful.\u201d<\/p>\n We may not have been aiming to make puppies or bunnies or donkeys that had floppy ears \u2013 just as we didn\u2019t set out to create the curly tail of a piglet or the mottled coat of the tortoiseshell cat \u2013 but they turned up just the same, an inevitable side-effect of tamer, more human-friendly animals. But then, whether because they were a necessary price to pay for not being eaten in our sleep, or because they signaled an animal could be trusted \u2013 or maybe we just thought they looked cute \u2013 we kept these traits, building for ourselves a fuzzy, floppy army of domesticated pets.<\/p>\n It was certainly a convincing theory \u2013 but would it survive scrutiny?<\/p>\n A more complex picture<\/p>\n With the neural crest argument, the origin of \u201cdomestication syndrome\u201d seemed tied up with a bow. But not everyone was convinced \u2013 and eventually, in 2023, the question was busted open once again.<\/p>\n \u201c[The] currently popular explanations aren\u2019t quite right,\u201d announced Australian National University ecologists Ben Thomas Gleeson and Laura Wilson in a 2023 article<\/a> for The Conversation. \u201c[We] propose a new explanation focused on big changes in the way domesticated animals live.\u201d<\/p>\n Arguments that domestication syndrome was some kind of side-effect of tameness \u201coversimplify and obscure the complex evolutionary effects at play,\u201d they wrote. The silver fox experiments, they argued, wasn\u2019t as definitive as presented \u2013 for one thing, the first generation weren\u2019t actually wild, but farmed; for another, symptoms of domestication syndrome had turned up even when Belyayev and Trut had bred for aggression rather than docility. Evidently, something more complicated is going on.<\/p>\n The key, Gleeson and Wilson found, wasn\u2019t so much which traits were being selected for, but which ones weren\u2019t. \u201cFor example, domesticated animals are often protected from predators, so wild traits for avoiding them might be lost,\u201d they pointed out. \u201cCompetition for mating partners is also often reduced, so wild reproductive features and behaviors could decline, or disappear.\u201d<\/p>\n \u201cDomesticated animals are also usually reliably fed,\u201d they continue. \u201cThis might alter certain features, but would certainly change natural metabolism and growth.\u201d<\/p>\n For wild animals, stiff ears have advantages. They help you hunt by better localizing sound; they stave off infections caused by trapped moisture and debris<\/a>; they\u2019re useful for thermoregulation<\/a> both in hot and cold weather. But when those features aren\u2019t being prioritized by the humans in charge of your breeding, they\u2019re not necessarily going to survive.\u00a0<\/p>\n In other words, floppy ears aren\u2019t something that turns up with domestication \u2013 they\u2019re something that disappears without it.<\/p>\n Hearing it out<\/p>\n![\"](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2025\/12\/267732.jpg\" "\\"")
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