Why Pets Have Surprisingly Small Brains


This video was sponsored by 23andMe. Hi, this is Emily from MinuteEarth. Domestication has puppified dogs, fluffified
sheep, and spotified horses – but there’s a less obvious physical change that virtually
all domesticated animals share: shrunken brains. Duck brains have shrunk by about 15%, cat
brains by 30%, and pig brains by a whopping 35%. We’ve even found smaller brains in farmed
trout. Which is weird, because in general, the size
of animals’ brains and the size of their bodies is super tightly linked – mites have smaller
brains than ants, which have smaller brains than mice, which have smaller brains than
elephants, and so on. The same relationship exists for individuals
within species. So, for example, small wolves have smaller
brains than big wolves, and small dogs have smaller brains than big dogs. But when you compare wolves and dogs, between
individuals of the same size, the wolves have bigger brains, no matter what the body size
is. What’s more, across different domesticated
animals, a disproportionate amount of the shrinkage happened in parts of the brain that
monitor information from the outside world and tell animals when and how to freak out
– sort of like the brain’s panic button. We know that, in general, animals with bigger
panic buttons have a more sensitive fight or flight response, and animals with smaller
panic buttons are naturally tamer. So those are the ones we probably would have
tried to domesticate. And, by breeding the tamest animals with each
other, we shrunk their panic buttons – and therefore their brains – even further. In short, domesticated animals have formed
long-term partnerships with humanity by literally losing their minds. Thanks to 23andMe for sponsoring this video. With 23andMe’s simple DNA kits, you can
learn all about your own ancestral history, as well as other parts of your DNA story,
like how your genes CAN influence everything from your facial features to your sleep quality. To get your kit, and show your support for
MinuteEarth, go to 23andMe.com/MinuteEarth. There’s a special holiday offer now through
December 26th; click the link in the description to get kits for you and your family.

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