Why is the chicken's knee facing back?
Why is the chicken's knee facing back?
In fact, the answer is simple: because it's not a knee.

when a chicken is walking, we seem to see it with a knee bent backwards. Why does it have knees in the opposite direction? In fact, the answer is very simple: because it is not a knee, it corresponds to a person's heel.

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the way we humans walk is called "metatarsal walking", which touches the ground on the soles of the whole foot, but many other animals, including birds such as chickens, are "toe walking", which is equivalent to the way humans stand on tiptoe. Only the front toes hit the ground. Their real knees are in a higher position, like humans, facing forward (pictured below).

(picture from: kirkkojyvaskyla.net)

although the appearance may be very different, the limb bones of animals all have very similar patterns. In the case of a person, the bones of the limbs are arranged like this: the one closest to the torso is a bone, the next one has two bones, then there is a pile of small bones at the corresponding wrist /ankle, and finally there are five sets of bones that make up the fingers /toes. This arrangement comes from a general "template", but animals have adapted to different modes of movement in evolution, and there have been a lot of changes in this pattern. Some bones have greatly changed their proportions, for example, the skeletons in bat wings are actually equivalent to extra-long "fingers", while others have changed in number, such as modern horses with only one toe (they are equivalent to landing on the tip of the middle finger). However, if you compare the limb bones together, you can still find many similarities, which also suggests that animals with limbs share a common ancestor.

(comparative pictures showing homology of limb bones, from left to right are: humans, dogs, horses, bats, birds, seals)

comparing the limb bones of different animals can bring a lot of inspiration, so there are many such comparison pictures. Some of it looks serious, but some of it looks like. The sand sculpture of riddles. The following is a sand sculpture version of the lower limb contrast picture, the creative idea is to pull human lower limbs to the same proportion as other animals:

(photo source: Kawasaki Goji)

the three animals behind humans are dogs, horses and flamingos. In fact, I just want to send this picture to write this push. I love it so much.