Not everybody gets the full quota of adult teeth. According to Wikipedia, "many people have less than the four [wisdom teeth]. Agenesis [failure to develop] of wisdom teeth is a normal condition that can differ widely by population, ranging from practically zero in Tasmanian Aborigines to nearly 100% in indigenous Mexicans.
I can corroborate this, at least in respect of some people having less than four (although I would say "fewer than four") wisdom teeth – as I only have two. My lifetime total of teeth is 50 (up to now ...)
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