Why do children grow milk teeth, and what’s their purpose? Why can’t they grow regular teeth directly?
In: Biology
Because baby teeth hold space for adult teeth to grow in.
Mammals stay on milk, which doesn’t require teeth, for a fairly long time in development, but breast milk has a lot of water in it, so it doesn’t have enough calories to feed a baby as they become a toddler, they have to start eating solid foods as they grow, which have more calories, but since the enamel (that shiny white outer layer of your tooth) doesn’t really grow and repair itself like the rest of your bones, teeth can’t really grow once they’re poking outside the gums.
So, we needed a way to have teeth come out, but the teeth can’t grow once they come out, we grow more teeth. This isn’t actually uncommon in the animal kingdom. Shark jaws grow a new tooth whenever they lose one, and rodent teeth just grow longer and longer. Our lineage of mammals only gets two sets, because the stem cells that tell your body to make more teeth die after the second set come in. For some reason, a way-back ancestor species we share with other mammals was the most successful not spending more energy on making more teeth than that.
That’s a trick mammals developed. The benefit is that our teeth fit perfectly into our jaw, wich allows biting things of cleanly and chewing efficiently (think about the effort a crocodile takes to bite something off, or how birds have to swallow things whole)
This means we can’t be born with teeth, and we can’t immediately grow adult teeth, because those wouldn’t fit into our (growing) mouth perfectly. This also means after birth we rely on being fed by our mother.
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