The brain is encased within a hard bone skull whose shape is designed to minimize the impact of blows. The ribcage does a relatively good job of providing protection to the internal organs.
By contrast, the neck is soft, fleshy, exposed, and an easy target with pretty much 100% kill certainty. Why is the neck unprotected by such defenses? Your jugular artery, trachea, and spinal cord are right there for the taking. Shrugging provides a slight measure of defense, but that defense is active, not passive.
Some of Homo sapiens’ features are genetic mistakes, such as knee joints that aren’t designed for upright walking or exposed humeral nerves. Is this one of those cases? Sounds to me like a deadly error.
Every feature we have is a genetic mistake. Our ape ancestors were in more danger of knocking their heads against something than having a rock smashed into their neck.
It’s not accurate to regard evolutionary developments as “mistakes.” Maybe the knee joints you describe (and the unarmored necks we possess) are less than ideal, but the existence of the human race is proof that these designs have been adequate to ensure the survival of the species.
Because the lack of neck armor isn’t a problem that tends to kill people off before they can reproduce.
Besides that - thick armor is fine for your skull, because the skull doesn’t have to move. But we need a flexible neck in order to do things like spot predators before they can get us. Or spot prey animals so that we can bash their heads in with rocks.
Name another animal that has a neck and also neck armor.
I can’t think of one – turtles and armadillos and glyptodonts are all superbly armored, but they don’t have neck armor. You want a neck to be mobile and twistable, to be able to move around easily. You want armor to resist attack, so you want it to be heavy and resistant, which is tough to mate with the requirements for a neck. Most things that want to protect that region effectively don’t have a neck, just good armor. About the closest thing I can think of is the skin of the Giant Ground Sloth, which apparently was thick and filled with tiny hard “calculi”.
Something will evolve if it’s possible by small modifications of the existing genetic code, and if it confers some survivability or sexual advantage. My suspicion is that it was too hard to develop an effective neck armor that conferred enough of an advantage to justify it (to put it all in human terms). Un-armored necks survived fine enough.
As noted, there aren’t “mistakes”, there are just the features we evolved with, despite how some designer might have done something differently. I think more serious errors are the vulnerable exposed front genitals, our very weak lower backs, and (especially) our inability to make Vitamin C. That last is apparently due to a genetic code error, because almost every other mammal has this ability. We’ve managed to survive with that error because we apparently lived where we could get vitamin C from our foods. But it did mean that eventually sailors would be suffering from scurvy when deprived of fresh vitamin C, while the rats on the same ships had no such problems.
What we have are a bunch of things with consequences. They are neither designs nor mistakes.
Ergo, they have no ‘purpose’.
We are here. We know that. Therefore, the consequences of the configuration we are generally left with as humans has allowed us to sustain ourselves as a species for a relatively short period of time so far (this is what we know), with the overall consequences of a armorless neck, decent eyes, decent ears, woeful sense of smell and other so-called shortcomings or flaws yet to be fully established… because we don’t know how long we will go on.
Even my terminology is flawed, because I say ‘decent eyes’. We don’t have ‘eagle eyes’, but it might be wrong to assume that such a trait would contribute to the survival of the species. Might not.
We do have neck protection, or at least men do, along with lions and certain fighting dogs: a big fluffy beard. Those throat ripping predators get a gob full of hair, we bash them with rock.
If I stab for your throat, what do you do instinctively without even thinking? You raise your arms and lower your head. Voila! a bony skull and jaw and two sets of bony and muscled arms are now covering your throat. You may have even dropped into a fighting crouch that put your hips back and shoulders and head slightly forward, making the throat and gut that much harder to hit.
Because the genetic mutation to have neck armor either never came about, or did, and conferred a negative reproduction advantage to whichever individuals had it.
Everythings a tradeoff. The shoulder joint is far more flexible than the hip joint, but the hip is far more stable than the shoulder. the advantages of a flexible neck have outweighed the drawbacks.
I’m going to WAG here and say that for a quadroped the throat isn’t that vulnerable and by the time we were bipedal there were easier places to hit us.
Minor hijack: how many predators actually specialize in neck/throat attacks?
Plus being bipedal, humans have a height advantage over other mammals in this respect. Add in some kind of sharpened stick to keep a predator at bay or kill it when it leaps, and it’s even better.
Eh - the exposed genitals are certainly inconvenient, but internal genitalia would cook the sperm, wouldn’t they? If you want to maintain sperm below ambient body temperature, you really can’t have them inside the torso. Can you?
Arguably the ceratopsians, though I think that the current consensus is that it wouldn’t have been strong enough, and paleontologists aren’t sure any more what the neck covering was for.
Making one of these, “why have we evolved this way?” threads is always really boring because a bunch of people come in and say the same real clever response about how ‘evolution doesn’t have a purpose!’.
Yes, yes, very clever. The point of the thread is, why does a lack of neck armor allow us to survive? Why aren’t we out-competed by genetic mutants with some serious neck armor? Answering “because we aren’t” is not helpful.
I would speculate that the reason humans, dogs, sheep, cows and a whole bunch of other mammals don’t have any neck protection is because it would slow down their ability to move their head and see their surroundings, which would be more likely to be fatal than not having neck protection once you’re attacked.
