Why do Humans not produce Vitamin C like other mammals?

Humans don't make Vitamin C like other mammals because we have a special kind of "shortcut" that doesn’t work quite right anymore.

Most animals, like dogs or cats, can make their own Vitamin C, just like how some kids can draw without tracing, they already know how. But humans are like those kids who had a special tool to help them draw, and one day it stopped working.

A long time ago, our ancestors could make Vitamin C in their bodies. But over thousands of years, we didn’t need to anymore, because we started eating lots of fruits and veggies that already have Vitamin C in them. It was like having a snack every day, so we didn’t need to make it ourselves.

Our body has something called an "enzyme", think of it like a special helper who makes Vitamin C for us. But humans lost that helper because of tiny changes in our DNA over time. It's like if you had a robot that helped you build your Lego castle, but one day it broke down and never fixed.

So now, we need to get Vitamin C from food, just like how some kids have to trace their drawings until they learn how to do them on their own.