Humans have 20 primary and 32 permanent teeth. The primary teeth’s shedding begins about age 5 or 6 and is finished by the age of 13. Wisdom teeth grow after adult dentition has replaced the first primary (milk) teeth, bringing the total complement to thirty-two.
Our ancestors, the early hominids, had large powerful jaw to tear and chew raw meat. They needed all 32 of their teeth, and they had plenty of room for them. But during evolutionary development as the humans took to cooking their food, their jaw size diminished. It was easier to deal with cooked food. Teeth also decreased in size, though at a slower rate, leaving less space for the wisdom teeth to grow into. As a result, their late arrival can cause painful overcrowding.
About 40 years ago it was common for dentists to extract molars to accommodate the newcomers. Since the introduction of fluoride toothpaste in the late 1960s, however, teeth are healthier and dentists are reluctant to remove healthy permanent teeth unless absolutely necessary. Instead, the wisdom teeth are pulled. We can manage very well without them. As the evolutionary changes most probably still continue, our teeth are likely to get smaller, but the process will be slow.
Third molar (Wikipedia)