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Originally Posted by Trish Crocker

"A wisdom tooth, in humans, is any of the usual four third molars. Wisdom teeth usually appear between the ages of 17 and 25.[1] Most adults have four wisdom teeth, but it is possible to have fewer (oligodontia), or more, in which case they are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or "coming in sideways." They are often extracted when this occurs. About 35% of the population do not develop wisdom teeth at all."

This is from Wikipedia

I heard or read that a modern human jaw is shorter from our human ancestors. So now the wisdom teeth no longer have the room in jaw.