system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the purpose of having baby teeth that fall out after a few years? Why don't we just keep the same teeth for our whole life?

And also, why do we only grow two teeth in our life? Why not more like sharks and other animals?
gpt
There's several ideas why.  A child's jaw isn't large enough to fit a full set of permanent teeth.  Also, baby teeth may serve as kind of a placeholder so that there will be enough space on the jaw for the permanent teeth to grow in.  The baby teeth save the spot of its corresponding permanent tooth until it's developed enough to replace it.  Children that lose a baby tooth early might experience problems with overcrowding of their permanent teeth.