Domestication Syndrome is a term used to describe the set of common physical and behavioural changes that often occur in animals living with humans. The syndrome might not be caused only by humans selecting animals for tameness, as domestication can be seen to have unintended shared effects from the new domestic environment. The removal of pre-existing selection can be just as important as new forces of selection. The hypothesis suggests multiple selective changes at work on domesticated animals, not just “selection for tameness,” as using this one term to describe them all is misleadingly vague, and obscures other changes in selection. Moreover, the new hypothesis highlights four ways that selection shaping wild animals is often disrupted by domestication. These include less fighting between males, fewer males for females to choose between, more reliable food and fewer predators, and elevated maternal stress. In effect, recognising multiple selective pathways better explains the domestication syndrome and reaffirms the complexity of evolutionary effects shaping all life on Earth.
In the 19th century, Charles Darwin observed a common occurrence among domesticated animals: the appearance of similar changes in different species when compared to their wild ancestors. Scientists refer to this phenomenon as “domestication syndrome.” Although the reason behind this collection of shared changes is still being hotly debated, it is generally accepted that tamer behavior is the most commonly shared change among domesticated animals. The theory is that ancient humans selected breeding stock for tameness. However, there are other shared changes that do not seem useful to humans or animals, such as shorter faces, smaller teeth, more fragile skeletons, smaller brains, and different colors in skin, fur, and feathers. Not all domesticated animals share all these features, but each change occurs in more than one domesticated species. A new paper published in Proceedings of the Royal Society B challenges popular explanations for domestication syndrome and proposes a new explanation focused on significant changes in the way domesticated animals live. Surprisingly, similar changes sometimes also appear in wild animals, leading some scientists to think they “self-domesticated” in some way. This theory also provides insights into how humans domesticated themselves.
Self-domestication, a phenomenon where animals undergo similar changes to those seen in domesticated animals, has been observed in several species, including the bonobo and urban foxes. This occurrence is most common in isolated sub-populations, such as those on islands, and may overlap with the “island effect.” Humans also show features of domestication syndrome when compared to our ancient ancestors, indicating that we also self-domesticated. Some scientists argue that these changes made us more sociable, helping us develop complex languages and culture. Therefore, understanding domestication syndrome in animals might improve our knowledge of human evolution.
Two main possible explanations have been put forward to explain domestication syndrome. The first suggests that ancient humans selected animals for tamer behavior, which somehow triggered all the other traits too. This idea is supported by a famous Russian fox-breeding experiment, which began in 1959, in which caged foxes were selected only for tameness but developed the other “unselected” features as well. The second hypothesis suggests that selection for tameness causes the other features because they are all linked by genes controlling “neural crest cells.” These cells form many animal features, so changing them could cause several differences at once.
However, a new research suggests that these two ideas oversimplify and obscure the complex evolutionary effects at play. Problems with the famous Russian fox experiment have been noted by other authors; for example, it did not begin by taming wild foxes, but used foxes from a Canadian farm that already had features of domestication syndrome. The experimenters didn’t only select for tameness; they also bred other foxes for aggression, but these foxes also developed domestication syndrome features. Therefore, a more comprehensive understanding of domestication syndrome is required, which takes into account the complex interplay of factors involved in animal domestication.
A similar experiment conducted in the 1930s showed that caged rats developed common changes, including tamer behavior, without any deliberate selection for tameness or aggression. This indicates that domestication syndrome may not be caused by humans selecting animals for tameness, but rather by unintended shared effects from the new domestic environment. A new hypothesis for domestication syndrome suggests that multiple selective changes are at work in domesticated animals, not just “selection for tameness.” The hypothesis highlights four ways that selection shaping wild animals is often disrupted by domestication, including less fighting between males, fewer males for females to choose between, more reliable food and fewer predators, and elevated maternal stress. These changes may resemble “selection for tameness,” but using this term to describe them all is misleadingly vague and obscures other changes in selection.
One current theory on human self-domestication is that sociable “beta males” began cooperating to kill alpha bullies. This led to fewer big and aggressive males, changing how competition worked among males. However, our hypothesis suggests that other effects also played a role. For example, our early ancestors evolved the capacity for shared infant care, which would likely trigger extreme stress for the mother in our chimpanzee relatives today. However, our ancestors adapted to this increased stress and gained an effective survival strategy. In effect, a clearer understanding of domestication syndrome in animals may improve our knowledge of human evolution as well.
A new study proposes that domestication syndrome, the shared features and behaviours observed in many domesticated animal species, might not be the result of intentional human selection for tameness. The research argues that unintended consequences of the domestic environment, which disrupts existing natural selection, are just as important. Domesticated animals have reliable access to food, fewer predators, and reduced competition for mating partners, among other changes. The hypothesis highlights four ways domestication disrupts selection, leading to shared effects: fewer males fighting, fewer males for females to choose from, reliable food, and elevated maternal stress. The researchers suggest that these shared selective pressures could explain the domestication syndrome seen across different species. According to the study, humans may have also self-domesticated, as the same syndrome can be seen in modern humans when compared to our ancient ancestors. A current theory is that sociable beta males started cooperating to kill alpha bullies, leading to fewer big and aggressive males, while our early ancestors evolved the capacity for shared infant care, which reduced maternal stress and allowed for a survival strategy. The study proposes that multiple selective pathways better explain domestication syndrome and highlight the complexity of evolutionary effects shaping life on Earth.
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