‘Domestication Syndrome’: Why do animals living with humans evolve similar features?

The most commonly shared change of domestication is tamer behavior. All domesticated animals are calmer than their wild ancestors naturally were. That's probably not very surprising. Ancient humans would've preferred docile animals, and likely selected breeding stock for tameness. But other common changes don't seem at all useful to humans—or to the animals themselves. Like shorter faces, smaller teeth, more fragile skeletons, smaller brains, and different colors in skin, fur, and feathers.

BEN THOMAS GLEESON: Charles Darwin was one of the first to notice something interesting about domesticated animals: different species often developed similar changes when compared to their ancient wild ancestors. But why would a host of seemingly unrelated features repeatedly occur together in different domesticated animals? Scientists call this collection of shared changes “domestication syndrome,” and the reason it occurs is still hotly debated…

The most commonly shared change is tamer behavior. All domesticated animals are calmer than their wild ancestors naturally were. That’s probably not very surprising. Ancient humans would’ve preferred docile animals, and likely selected breeding stock for tameness. But other common changes don’t seem at all useful to humans—or to the animals themselves. Like 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. For example, dogs have many, and camels only a few. But each change occurs in more than one domesticated species… Perhaps more surprisingly, modern humans also show features of domestication syndrome, when compared to our ancient ancestors. This suggests we also self-domesticated. Some scientists argue these changes made us more sociable, helping us to develop complex languages and culture. So a clearer understanding of domestication syndrome in animals might improve our knowledge of human evolution too…

In recent years, two main possible explanations for domestication syndrome have dominated scientific discussion. The first suggests it was caused when ancient humans selected animals for tamer behavior, which somehow triggered all of the other traits too… The second hypothesis complements this first one. It suggests selection for tameness causes the other features because they’re all linked by genes controlling “neural crest cells.” These cells, found in embryos, form many animal features—so changing them could cause several differences at once.

However, our new research suggests these two ideas oversimplify and obscure the complex evolutionary effects at play… it seems domestication syndrome might not be caused by humans selecting animals for tameness. Instead, it might be caused by unintended shared effects from the new domestic environment…

For example, domesticated animals are often protected from predators, so wild traits for avoiding them might be lost. Competition for mating partners is also often reduced, so wild reproductive features and behaviors could decline, or disappear. Domesticated animals are also usually reliably fed. This might alter certain features, but would certainly change natural metabolism and growth.

In effect, we argue there are multiple selective changes at work on domesticated animals, not just “selection for tameness,” and that shared shifts in evolutionary selection would often cause shared changes in features. Even across different species… So how did we domesticate ourselves? Well, one current theory is that sociable “beta males” began cooperating to kill alpha bullies. This changed how competition worked among males, leading to fewer big and aggressive males.

But our hypothesis suggests other effects also played a role… More reliable food access due to group foraging and sharing, plus collective defense against predators, might also have made us more sociable, more cooperative, and more complex, while promoting other changes commonly seen in non-human domesticated animals. Whatever the specific drivers in each species, recognizing multiple selective pathways better explains the domestication syndrome, and reaffirms the complexity of evolutionary effects shaping all life on Earth. SOURCE…

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