After all we don’t lose our baby fingers or our baby ears. Why can’t the teeth just get bigger like everything else in our bodies?
I’ve actually asked this question of two dentiists, one a pediatric dentist, and neither had any idea. In fact they acted like they’d never even thought about it before.
My WAG is that once the enamel sets it makes it impossible to grow the tooth any larger, much like your head stops expanding when the plates finally fuse.
Nature did an end-run around this issue by replacing the lil’ ones with growd-up ones, once our head was of a more mature size.
I did wonder if it has anything to do with decay from all that lactose.
Actually, losing and replacing teeth is so prevalent among chordates that I wonder if it was selected for back in the primordial ooze and simply came with us all this time or if it is such a “natural” strategy that it is redeveloped among hundreds of species. Not all chordates (or even mammals) follow the same process as humans with a single set of post-natal teeth followed by a seond set, but the practice of losing and re-growing teeth in some form is rather widespread.
I would guess that teeth need to be quite a bit harder than nails/claws/talons. The energy to make them grow continually might simply be too high an investment to make, so different species grow different numbers of sets to specific sizes.
Ok, so given how painful bad teeth are, and how up until recently the most common way to solve serious problems was to pull the tooth, why don’t we have more than two sets of teeth? The reason I thought of is somewhat disgusting, so I knew people would be interested: Adults must have teeth to be able to chew food properly. When they’re taking care of very young people with no teeth or poor teeth, or old people with the same condition, the adults in prehistory with good teeth could chew the food for others. Ick.
No wonder that lifestyle didn’t encourage historians… “Dear Husband, same ol’, same ol’: spent what part of the day I wasn’t cooking meals chewing it up for boo-boo and grandma. Hope the mammoth hasn’t knocked out any more of your molars, we’re running short…”
I don’t think it has to do with decay, since I personally have had most of my baby teeth for nearly 30 years, and I’ve never had a cavity. (I have a rare condition which causes your adult teeth to not grow in, so the baby teeth don’t fall out)
Cool! Are your teeth smaller than average or do they look normal?
In most animals, the primary purpose of teeth is prey capture: you grap onto something, and the teeth help prevent it from escaping your maw. They also create punctures, through which digestive enzymes can penetrate into the hunk of food and begin digestion.
As one might expect when using one’s mouth to grapple with one’s prey, some teeth will almost invariably get knocked out. Thus, a replacement strategy tends to be good thing. A good many animals have polyphyodont teeth, meaning they are continuously replaced throughout the animal’s lifetime.
Mammals, not surprisingly, are a bit different. For one thing, they chew their food, which allows digestion to begin in the mouth, rather than waiting until food enters the gut. As such, a simple, continuous replacement is probably not going to be the best strategy. Better to have a set of more permanent choppers which are less likely to get knocked out while grappling with prey, seeing as how those same teeth will be needed to start chewing on your prize, once it’s subdued. Better still to have all of one’s teeth occlude properly; having all of one’s teeth erupt more or less at once helps limit the number of gaps in the chewing surface.
Mammals, in general, have what are termed diphyodont teeth, meaning they only have two generations of teeth. The first set, during the suckling phase (something else which mammals do differently, of course), consists of incisors, canines, and premolars. The second, permanent, set adds molars to the list. Note that during the suckling phase, the teeth don’t tend to occlude nicely. This isn’t generally a problem at this stage, since the animal isn’t really chewing anything.
The replacement tooth forms from a combination of the dermal papilla and the enamel organ, which each lie deeper in the jaw than the roots of the “deciduous” (or “milk”) tooth. As the second-generation tooth grows, it gradually cuts off the nutrient supply to the milk tooth, which causes the root of the milk tooth to be reabsorbed, thus loosening it. Eventually, of course, it falls out, and the second-generation tooth soon takes its place.
It seems to me that such a system would be advantageous because a) during suckling, it probably limits damage caused by devloping teeth to the nursing mother (being bit on the nipple is probably not amongst life’s finer pleasures), and b) once weaned, it was important to have properly occluding teeth for chewing purposes, so further tooth production was simply shut down. This helped ensure that all teeth in the adult would be of the same generation, thus decrease the number and size of gaps between upper and lower teeth.
As was stated above some animals will have more than two sets of teeth in their lives because of continious wearing away. Back in pre-historic times the life expectancy of man was probably no more than 30 to 40 years and so our two sets of teeth would have been enough. It is only that we are living much longer now that the lack of teeth replacement is noticed.
Actually, not so cool. They’re extremely screwed up looking, very small, and baby teeth roots are not so good (i.e. they move around a lot and hurt). I don’t recommend it.