By Galadriel Watson<\/p>\n\n\n\n
August 23, 2022 at 9:15 a.m. EDT<\/p>\n\n\n\n
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When its owner arrives home, a dog may seem to smile. When a dog wants to go for a walk, it may lift an eyebrow and look pathetic. These adorable expressions have helped create a \u201cdeep, long-standing bond between humans and dogs,\u201d says Anne Burrows, a professor of physical therapy at Duquesne University in Pittsburgh, Pennsylvania. They also make dogs unique when compared with species such as wolves or cats.<\/p>\n\n\n\n
Burrows and her team discovered that domesticated dogs have a muscle in the eyebrow region that gray wolves don\u2019t: the levator anguli oculi medialis<\/em>. \u201cThis allows dogs to make that puppy-dog-eyes face,\u201d says Burrows. \u201cAnd wolves just don\u2019t make that face.\u201d<\/p>\n\n\n\n They also studied two muscles around the mouth: the orbicularis oris and the zygomaticus major. Both dogs and wolves do have these muscles. In dogs, however, they\u2019re mostly composed of fast-twitch fibers. In wolves, they\u2019re mostly slow-twitch.<\/p>\n\n\n\n To understand what this means, Burrows says to think of human runners. \u201cIf you\u2019re a sprinter, you\u2019re going to run really fast but only for a short distance. Your leg muscles are probably dominated by fast-twitch fibers,\u201d since these can contract quickly.<\/p>\n\n\n\n \u201cIf, though, you\u2019re a marathon runner, you might take a while to get up to speed, but you\u2019re going to last a long time. So marathon runners probably have leg muscles that are dominated by slow-twitch fibers.\u201d These shift more gradually into motion but then don\u2019t get tired as soon.<\/p>\n\n\n\n A dog with primarily fast-twitch fibers, therefore, can quickly make facial expressions. (Humans are fast-twitch face-makers, too.) These fibers also mean they\u2019re great at barking, \u201cwhich is a really fast movement of the lips.\u201d<\/p>\n\n\n\n On the other hand, wolves\u2019 muscles are perfect for extended movements \u2014 such as howling. \u201cThey kind of turn their mouth into a funnel, and they hold that contraction for, you know, 30 seconds maybe,\u201d Burrows says.<\/p>\n\n\n\n But why are dogs\u2019 and wolves\u2019 muscles and behaviors different? One possibility is that, when humans were first domesticating wolves \u2014 which would eventually become what we now know as \u201cdogs\u201d \u2014 \u201cthey were choosing this animal that barked instead of howled,\u201d Burrows says. Some 40,000 years ago, people were deciding to hang out with dogs that were good at creating alarm calls, such as indicating when a stranger was outside. It just happened to be that these dogs \u2014 the ones with more fast-twitch fibers than slow-twitch ones \u2014 could also make the sweetest faces.<\/p>\n\n\n\n Then again, maybe those ancient humans felt a stronger bond with dogs that could look cute and the barking trait was a bonus. After all, gazing into a dog\u2019s eyes is known to release a hormone called oxytocin (ox-see-TOH-sin) in both human and dog. \u201cIt\u2019s thought to be a love hormone, a hormone that promotes bonding,\u201d Burrows says.<\/p>\n\n\n\n As for pet cats, they have similar facial muscles to dogs but don\u2019t generally use them to peer at us longingly. Instead, they\u2019re mostly used to control their whiskers, which help them navigate their environment. Those movements don\u2019t usually get an emotional response from humans.<\/p>\n\n\n\n \u201cI love my cats,\u201d Burrows says, \u201cbut in a different way.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":" Certain muscles help make dogs \u2018smile\u2019 or raise an eyebrow, expressions that help them bond with humans. From The Washington Post By Galadriel Watson August 23, 2022 at 9:15 a.m. EDT When its owner arrives home, a dog may seem to smile. When a dog wants to go for a walk, it may lift an eyebrow […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12,33,1],"tags":[],"class_list":["post-4609","post","type-post","status-publish","format-standard","hentry","category-dogs","category-human-animal-bond","category-uncategorized"],"yoast_head":"\n