Like, when you pet a dog/cat, their skin is sort of looser, they have a scruff of the neck and lots of rolls. But in humans, the skin is tight on the meat, even on the hairy parts like the scalp. Is there a reason for this?
In: Biology
humans have a lot different “natural defenses” than most other animals.
for the most part that scruff and thick loose layer of skin on wild animals exists to protect their organs and other vital parts during a fight. they can claw and bite at each other and rip this to shreads without always being fatal.
By-and-large loose skin animals don’t sweat. That loose skin allows them to release more heat through their skin. This is because, when mammals are hot, blood will flow outwardly into the skin and outer muscle to help cool the core. Looser skin allows for more surface area to do that.
While we do that as well, we can sweat meaning we need skin with a more taught surface that’s easily exposed to the environment for the sweat to have something good to evaporate from.
The only common exception are porcine mammals which roll in water/mud to cool in a similar way to our sweat. Elephants have loose-ish skin and massive ears they use to keep cool.
Most dogs have loose skin. dogs bred to keep wolves away from livestock tend to have even loser skin than most dogs. Most mastiffs if you grab them by the scruff of their neck, can turn their heads fully around and bite you, which is not an accident of genetics.
Cats and dogs are predators, but they are also prey animals. Having loose skin means that even if a predator grabs them, their skin is loose enough that they can still have a pretty good range of motion to fight back.
Humans and our recent ape ancestors have had other ways of avoiding predation. Mostly, climbing trees or getting to a high spot, working as a group to fight back, and inventing weapons. In fact, one theory about why human ancestors might have began walking bipedally is because it allowed them to see over the tall grasses in their habitat so they could see predators coming and avoid them.
Skin is divided into multiple layers and sections. Humans have a thin subcutaneous layer (under the skin) and above the fascia and muscle/fat compared to other animals. Cats, dogs and other animals have a thicker layer compared to humans. This later provides a slippery, loose structure compared to humans. For comparison, on a beagle you can easily inject 400-500mL of liquid under the skin while with a human it would be very difficult and painful to get more than approximately 100-200mL. It’s a common thing for pets to get this for dehydration, for humans you can look up “bagel heads”
Another fun factor is about shedding water.
Animals with fur that get wet need to be able to quickly dry off (or risk freezing).
Loose skin means that the wet-dog-shake has extra momentum and “whips” a bit, sending more water flying than if the skin was tight.
Evolutionary features like this often have many benefits, because evolution is frugal and there are many problems to solve.
i wondered if my cat was getting too big, turns out that extra skin on her belly is for protection in a fight.
the pooch belly is a good thing : )
Animals skin (at least dogs, which is where my experience with this is coming from) isn’t attached to their bodies the same way our skin is. I’m not going to pretend to understand on a scientific/biological level, but I know that for my dads terriers it apparently something to do with self defence like an animal can get a mouthful but the dog can still twist and roll around where as if I pinned your shoulder skin in a vice you aren’t turning around to do shit about it without tearing something
What everyone else said but also certain injuries that they may receive, like a tear in their esophagus for example, can cause the space between their bodies and their skin to blow up like a balloon. It is called subcutaneous emphysema. I am not sure what the evolutionary advantage to this is but once the air starts to go down you can pet them on the head it feels like very tiny bubble wrap popping under their skin each time you touch them. Not a very suitable explanation for a five year old, but hopefully interesting.
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