Given the likelihood in nature of being attacked and wounded, how come they never came to have more hardened skin to prevent being penetrated so easily?
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Humans have pretty soft skin, too. There’s a video going around of a bear landing what is clearly a fairly soft “scratch” on a man’s belly and the attack tears some pretty nasty gashes in him.
A lot of mammals have softer skin than humans because they have a layer of fur to protect it. Fur provides more protection than you might think.
But if you’re looking for the most direct, most objective answer: It’s because soft skin hasn’t hindered their ability to procreate. Evolution doesn’t aim for “best,” it just aims for “good enough.” Soft skin requires less resources for the body to create than thick, hardened hides, so if a species can survive without the extra resource expenditure, evolution won’t steer them that way.
Harder skin surface gives relatively little benefit in relation to what it takes away: Being agile, having secrition glands on it’s surface, having harder time with thermal regulation, requiring more nutrition to keep that skin hard etc.
Remember that when it comes to evolution the strongest selective preassure isn’t the predators, it’s the enviorement itself, that’s why it’s “survival of the fittest” and not “survival of the strongest”. If something can protect you from being eaten but it makes you more likely to die from overheating, or makes it harder for you to get food or anything like that, then it likely won’t be passed down to future generations. Of course there are exceptions to that like to pretty much every rule in biology that exists.
All characteristics come at costs, and provide different benefits. Hard or rigid skin may protect from wounds better in some cases, but it can reduce sensitivity, mobility (light-weight is good!), flexibility, and once you are wounded there are cases where it’s harder to heal. Not to mention heat exchange and the like, or the resources required to grow and maintain denser skin. For some animals it makes sense, for a lot, the cost is too high. You’d be better off running away or healing from minor wounds (also a + with soft tissue often) than losing a chase and *having* to endure being penetrated.
So yeah. Most creatures tend to be durable on the parts they need. Hooves, claws, teeth, feet, those kinds of things. And, vital organs get their own protection. The rest? Not so much, unless their environment/predators call for it.
Idk what these comments are talking about. Most animals have evolved thick hides because it is indeed an evolutionarily beneficial adaptation. This adaptation is most frequently exhibited in animals that are prey animals, and not hunting animals. Hunters need to be agile and nimble, while prey animals need the extra protection. Both sets of animals have evolved according to this difference in need.
If we’re talking about animals in general, having a hard outer surface like a beetle, clam, or alligator seems to be more common than a soft outer surface like a jelly or hummingbird. Both strategies work once you consider other defenses like agility and toxins.
Humans use basically our entire skin to radiate heat; it gives us really good endurance (though most people don’t train for it these days), but we’re much easier to slash and stab than, say, a pig.
>OP: “never came to gave more hardened skin”
OP’s question implies that no animals ever have evolved thick hide or armor.
Elephants, Rhinos, Hippos, Crocodilians, Armadillos, Walruses, Whales, sharks, Bears, literally all chitinous insects and arthropods.
Those are just off the top of my head animals that have either thick hard skin or something similar like blubber or thick fur that acts as an external barrier between a predator and internal organs.
Ultimately though, survival is about trade-offs and adapting to the environment at hand, not finding some universal perfect form. If your skin is too thick or hard, you lose mobility and the ability to find food efficiently or escape from other kinds of danger that armor can’t protect against.
And pretty much the answer to any question that is “why does animal X have characteristic Y”, it’s because characteristic Y was very helpful at some point to animal X’s ancestors, which at some point mutated some subtler version of characteristic Y before it was useful, and so every individual that had that already had that characteristic when it suddenly became useful in that environment, survived longer and had more children than the individuals that didn’t have it, and that characteristic became more and more exaggerated in each future generation that it was passed down to.
many animals DO have hard skin (reptile scales)…and even armored exoskeletons (insects/Arthropods/Crusteceans).
‘Animal’ is a *very* broad term and I’m guessing you meant is why do most *mammals* have soft skin, which is likely to do with the fact mammals bodies can sustain their own inside temperatures and were warm blooded?
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