for something so important to the body, why does our bodily unable to produce its own vitamins?
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Our body is not entirely unable to produce its own vitamins.
It can’t produce all of them, but we produce vitamin D from sunlight exposure, for instance.
Ultimately though, we’re not a chemistry set. Sometimes you have to have the right things in the right shapes to start with.
For something so important to the body, why is our body unable to produce oxygen? The simple answer is that it hasn’t needed to.
We can breathe in what we need from the air around us. We’d be in a lot of trouble if we ended up in an environment without oxygen, but 99.99% of us don’t die of suffocation, so it’s good enough. Even if it were possible to evolve an organ that produced enough oxygen to get by, that organ would need resources, and increasing our daily calorie count/nutrition requirements would likely have killed more humans via starvation than being able to breath underwater or while being strangled would have saved.
Similarly, we’ve been able to get enough vitamins from our diets to get by for the entire history of our species. Could we have evolved ways to produce them? Probably, but we’d still have to eat more of the ingredients for them. If we can just eat them, it’s easier to do that.
Produce them from *what?*
Let’s imagine we had an enzyme that could produce, say, Vitamin A. Well, that enzyme has to produce Vitamin A *from some precursor*, because our bodies cannot just conjure the required atoms into existence. And that just moves the problem back one step – now we have to consume that precursor, so that precursor is now an essential vitamin.
Ultimately no form of life makes *everything* it needs to live – at some level *everything* has to get *something* from the environment around it, because the law of conservation of mass implies that everything we make has to be made of something else that already existed.
Turn it around; if our bodies could produce every vitamin we needed with no issues, we wouldn’t think of them as important.
Also, as one case study, I think humans used to be able to make Vitamin C in our bodies, but the gene for that got corrupted. At the time, we were getting enough of it from our food anyway that there was no evolutionary pressure to keep the ability, so instead of everyone dying out who couldn’t synthesize Vitamin C, it just stuck around.
It is because of the process of “specialization”.
Basically, humans’ evolutionary ancestors stumbled upon a situation where their cells didn’t need to make *everything* themselves because it was easier to get those resources by eating them… until eventually they came to rely on an ecosystem of many many situations like that.
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Think about having a typical “desk job” at some big corporation somewhere. Maybe you need a car to get to work, and a computer to read emails, and a telephone to make calls, and some clothing to wear, and some food to eat, etc. Those things are probably all pretty important and necessary… but just imagine for a second that you couldn’t just *buy* those things somewhere, but had to make them “from scratch”.
First you’d need food. So, you’d have to know how to farm, and be good at it enough to survive.
Then you’d need clothes. So you’d have to know how to make thread, and weave cloth, and sew clothes.
Then you’d have to know how to mine metals, and forge steel, and machine things, and assemble things.
Then you’d have to learn how dig up oil, and refine it into plastics, and make injection molds.
Then you’d have to know about semiconductor materials, and manufacture silicon wafers, and do photolithography.
And if you learned how to do all of those things so well and so fast, you might one day eventually be able to get to your desk job of making calls and reading emails.
…but that’d be really really really complicated.
Instead, some people specialize in farming. They do it really well, and don’t bother with the other skills so long as doing “their job well enough” means that they are able to buy the other things they need from a store elsewhere.
And some people just make thread, and others just weave, and others just sew. They do it really well, and are able to buy the other things they need from stores elsewhere.
And some people mine, and some people do metallurgy, and some people drill oil wells, and make silicon wafers, and do this, and do that, and yada yada, etc. They do it really well, and are able to buy the other things they need from a store elsewhere.
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Nature is kinda like that too. (Except a bit more harsh in that critters are eating other critters are eating plants, etc.)
We don’t have to make Vitamin-A “from scratch” because it has just been so much easier to go eat some carrots or whatever, and that gave our evolutionary ancestors more opportunities to specialize in other areas.
“Since the head is so important to the body, why cant we just grow it back when we lose it?”
Such a great question
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