I mean.. we grow teeth a total of 3 times. The first for our baby teeth, the second time for our 'mature' teeth, and the make up 'wisdom' teeth to fill any that might've fallen out at that point. I'm guessing those three growths were the most needed for humans early survival before we got all fancy with farming and hygiene. At which point we kind of broke survival of the fittest and things just kind of happen now.
Kind of like how humans are one of a handful of mammals that didn't evolve out of menstruation.
I had to read more about it myself and I am mistaken in the origins of it. It's not that most other creatures evolved out of it, we're just one of the 'lucky' few to develop it.
I think they are intended to, and they actually do... once (child teeth). Probably just broken due to genetic decay or environment (e.g. if humans are no longer fully maturing and what we call adult teeth are actually "intermediate" teeth). I suspect a deeper understanding of the recent tooth-regrowth drug(s) may provide a clue as to why it is currently broken.
You said exactly why in your post: "...our biological design..."
There's no such thing. We evolved. That means we're a mix of traits passed along over time by individuals that managed to live long enough to breed.
That's it. That's the whole explanation for any question about "why don't humans do x thing as part of our biology?"
Any given trait is all about lasting long enough to make babies. Once that occurs, all that's left is a general proclivity to ensuring the babies survive long enough to do the same. Regrowing teeth isn't part of that. It's a niche trait that isn't as useful as you'd think for humans. We don't need to gnaw at things, we don't need to crack bones with our mouths, nothing that would make a third set of teeth an advantage, or different teeth an advantage.
Teeth are not easily breakable. We actually can crack bone with our jaws and the teeth will usually survive if the bone isn't too thick; we just have better tools for that because way back when, the proto-humans that used tools had more babies that survived to make more babies. You have to abuse and/or neglect your teeth to break them for the vast majority. There are congenital issues where that isn't the case, but we've also bred ourselves into a social species that takes care of each other, so we aren't limited to a harsh, primitive survival level of things.
I really don't get why people think of teeth as fragile. They're incredibly durable for what we need them for, and require only minimal care to last well beyond breeding age. Even if you factor in modern diets being bad for teeth, regular care for them (brushing and flossing) can stave off those effects for decades. Go search up some of the dental research on old human bodies from archaeological sites. People survived very well with just one set of adult teeth.
And, some humans do have extras that can come in later in life, though it's very rare and comes with drawbacks (according to the last lady I dated that was an anthropologist anyway). Supposedly, having the extras actually weakens the regular adult teeth and makes them more prone to damage. There's always a tradeoff in things like this.
I think there just hasn't been an evolutionary need for them to regrow. In past millenia, people had kids and died before toothlessness really became an issue and teeth lasted longer before our modern industrial diet.
People with healthy diets don't need them to, and there are advantages to teeth secured very tightly into our jaw. Teeth are actually very strong and resilient.
And when people do start losing teeth, it mostly happens past the age of reproduction to the evolutionary impact is lessened. On an evolutionary scale, we've only fucked up our diets with sugar and processed foods very recently. Plus, we now have dentistry to reduce that impact, so I doubt evolution will make it happen to humanity in the future.
There are actually people that grow more teeth, but they have more complications than advantages. I suspect this has been the case historically as well. If everyone else can do with just the normal amount of teeth, these people don't get an evolutionary advantage and their teeth gene quirks don't become common among humans.
That said, scientists are working on stimulating teeth growth for people who have lost them or never had them. It's not impossible, it seems, just very difficult.
I know the point of your answer was not to dwell on these things, but:
And what would a chair look like if our knees bent the other way?
Is actually very interesting, would've we designed it as a normal chair but we would rest our chests instead of backs? Or would they have a place to rest the legs instead of on the floor?
We can. We figured out how. Thousands of humans fly every day across the planet faster than any bird. We can also live in environments we were definitely not designed to whether it’s with clothing, fire, or advanced HVAC systems. And we’ve pushed that further with our own little atmospheres under the sea or in space.
Evolution didn’t stop with us. It is us. Evolution, in trying every possible permutation possible landed on an organism that adapts the world around it, rather than waiting generations to adapt to the world around it.
Now it’s a matter of if our social and societal evolution will see us succeed or end in failure. If we don’t solve the climate crises we created, if we end up murdering each other, if we get smacked by an unforeseen object from space, potentially built by even more advanced evolution, we lost, and evolution will continue. Evolution is us, but far too often we’re too blind to see that gift, and advance responsibly
The diet that we evolved to consume (fruits, lean meats and fibrous plants) was much less damaging to our teeth than the current high-sugar, high-fat, highly processed foods. And human lifespans was shorter, so less time for teeth to damage.
So there wasn’t a strong evolutionary need to regenerate them (unlike an animal like sharks)
I believe that humans were created by an ancient race of machine-men that used biology the same way we use machines. When we became self-aware we destroyed them and lost all prior knowledge.
Now we’re on the brink of creating the next race of machine men that will destroy us only to repeat the cycle until the end of time.
First there was God, then came the monkey, then came the robot! Then there was God, next came the monkey, then came the robot! Again there was God, then came the monkey, then came the robot!
Or we were designed with planned obsolescence in mind. I mean, we can pretty much do everything to keep a human alive for a long, long time... But the cells themselves have an expiration date and after that point they simply stop replicating. It's like the last puzzle to solve for figuring out immortality.
Mammals have fuck all in terms of adaptability tactics. Only way for us to adapt, is mix our genes and hope it suffices. The only way we can do that, is reproduction (funghi are op). Now that means more of us in a system that has limited resources (called carrying capacity). We die in order to prevent competing with our children.
This is the reason animals have different lifespans depending on how likely they are to survive in nature. Take a rat and north american opossum for example. Far apart in terms of evolution and size, but have roughly the same life expectancy due to predation. Wolves can technically live up to 17 years, but become fertile at a very young age because the average lifespan in the wild is 5 years due to disease.
It is also the reason menopause exists. It is rare, and found in elephnts and orca's (both matriarchial species) and humans. This is because the life experience of the matriarch is too valuable. To be able to keep the matriarch around without her being able to compete with her own offspring, infertility is incuded. Post-menopausal orca's pimp out their youngest sons because it is the best way to pass on genetics they have left. Imagine your mom being your finman.
Humans are the odd one out here since we also have andropause, the male equivalent. A paradox on male reproductive strategy. Which afaik doesn't exist anywhere else. This is why humans live so long compared to most mammals. Grandparents are important.
Some animals don't really age. Lobsters simply die from growing too big and unable to get enough oxygen. Some species of octopi stop eating after mating all the way to starving to death. Some animals mate until they die from exhaustion. The immortal jellyfish pretty much recycles itself. And bot just animals need death for renewal. New zealand has a forest which reproduces only after a forest fire. Which happen rarely over hundreds of years due to being in a region with lots of heavy rain. The trees themselves are pretty much immortal, and don't reproduce while living.
Senesence and death are essential for ecosysems and adaptation of life. Regardless of whether or not keeping an aging body alive is hard or possible.
We age because our cells "choose" to. We have the equipment to live on "forever." It's just not our meta.