How did teeth evolve? - Peter S. Ungar
-
0:07 - 0:11You may take them for granted,
but your teeth are a marvel. -
0:11 - 0:14They break up all your food
over the course of your life, -
0:14 - 0:18while being strong enough
to withstand breakage themselves. -
0:18 - 0:21And they’re formed using
only the raw materials -
0:21 - 0:24from the food they grind down
in the first place. -
0:24 - 0:27What’s behind their impressive strength?
-
0:27 - 0:31Teeth rely on an ingenious structure
that makes them both hard and tough. -
0:31 - 0:36Hardness can be thought of as the ability
to resist a crack from starting, -
0:36 - 0:39while toughness is what stops
the crack from spreading -
0:39 - 0:42Very few materials have both properties.
-
0:42 - 0:46For instance, glass is hard but not tough,
-
0:46 - 0:49while leather is tough but not hard.
-
0:49 - 0:52Teeth manage both by having two layers:
-
0:52 - 0:57a hard external cap of enamel, made up
almost entirely of a calcium phosphate, -
0:57 - 1:01and beneath it,
a tougher layer of dentin, -
1:01 - 1:04partly formed from organic fibers
that make it flexible. -
1:04 - 1:08This amazing structure is created
by two types of cells: -
1:08 - 1:11ameloblasts that secrete enamel
-
1:11 - 1:14and odontoblasts that secrete dentin.
-
1:14 - 1:17As they form teeth,
odontoblasts move inward, -
1:17 - 1:22while ameloblasts move out
and slough off when they hit the surface. -
1:22 - 1:26For enamel, this process produces long,
thin strands, -
1:26 - 1:29each about 60 nanometers in diameter.
-
1:29 - 1:32That’s one one-thousandth
the width of a human hair. -
1:32 - 1:36Those are bundled into rods,
packed together, -
1:36 - 1:38tens of thousands per square millimeter,
-
1:38 - 1:42to form the shield-like enamel layer.
-
1:42 - 1:45Once this process is finished,
your enamel can’t repair itself again -
1:45 - 1:49because all the cells
that make it are lost, -
1:49 - 1:52so we’re lucky that enamel
can’t be easily destroyed. -
1:52 - 1:58Odontoblasts use a more complex process,
but unlike ameloblasts, they stick around, -
1:58 - 2:02continuing to secrete dentin
throughout your life. -
2:02 - 2:05Despite the differences in teeth
across the mammalian order, -
2:05 - 2:10the underlying process of tooth growth
is the same whether it’s for lions, -
2:10 - 2:11kangaroos,
-
2:11 - 2:12elephants,
-
2:12 - 2:14or us.
-
2:14 - 2:17What changes is how nature sculpts
the shape of the tooth, -
2:17 - 2:19altering the folding and growth patterns
-
2:19 - 2:23to suit the distinct diets
of different species. -
2:23 - 2:29Cows have flat molar teeth with parallel
ridges for grinding tough grasses. -
2:29 - 2:34Cats have sharp crested molars,
like blades, for shearing meat and sinew. -
2:34 - 2:39Pigs have blunt, thick ones,
useful for crushing hard roots and seeds. -
2:39 - 2:42The myriad molars of modern mammals
-
2:42 - 2:45can be traced back to a common form
called “tribosphenic," -
2:45 - 2:48which first appeared
during the dinosaur age. -
2:48 - 2:52In the 19th Century,
paleontologist Edward Drinker Cope -
2:52 - 2:55developed the basic model
for how this form evolved. -
2:55 - 2:59He hypothesized that
it started with a cone-like tooth, -
2:59 - 3:02as we see in many fishes,
amphibians, and reptiles. -
3:02 - 3:07Small cusps were then added,
so the tooth had three in a row, -
3:07 - 3:11aligned front to back,
and connected by crests. -
3:11 - 3:16Over time, the cusps were pushed out
of line to make triangular crowns. -
3:16 - 3:21Adjacent teeth formed a continuous
zigzag of crests for slicing and dicing. -
3:21 - 3:25A low shelf then formed
at the back of each set of teeth, -
3:25 - 3:28which became a platform for crushing.
-
3:28 - 3:33As Cope realized, the tribosphenic molar
served as the jumping-off point -
3:33 - 3:36for the radiation of specialized
forms to follow, -
3:36 - 3:38each shaped by evolutionary needs.
-
3:38 - 3:41Straighten the crests
and remove the shelf, -
3:41 - 3:45and you’ve got the conveniently
bladed teeth of cats and dogs. -
3:45 - 3:50Remove the front cusp, raise the shelf,
and you’ve got our human molars. -
3:50 - 3:54A few additional tweaks get you
a horse or cow tooth. -
3:54 - 3:58Some details in Cope’s intuitive
hypothesis proved wrong. -
3:58 - 3:59But in the fossil record,
-
3:59 - 4:03there are examples of teeth
that look just as he predicted -
4:03 - 4:08and we can trace the molars of all living
mammals back to that primitive form. -
4:08 - 4:12Today, the ability to consume
diverse forms of food -
4:12 - 4:14enables mammals to survive in habitats
-
4:14 - 4:17ranging from mountain peaks
and ocean depths -
4:17 - 4:19to rainforests and deserts.
-
4:19 - 4:24So the success of our biological class
is due in no small measure -
4:24 - 4:26to the remarkable strength
and adaptability -
4:26 - 4:29of the humble mammalian molar.
- Title:
- How did teeth evolve? - Peter S. Ungar
- Description:
-
View full lesson: https://ed.ted.com/lessons/how-did-teeth-evolve-peter-s-ungar
You may take them for granted, but your teeth are a marvel. They break up all your food over the course of your life, while being strong enough to withstand breakage themselves. How do they do it? Peter S. Ungar traces the evolution of mammalian molars from primitive cone-like structures to the myriad forms of today’s species, from lions to cows to people.
Lesson by Peter S. Ungar, animation by Cabong Studios.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:45
Michelle Mehrtens edited English subtitles for The evolution of teeth - Peter S. Ungar | ||
Michelle Mehrtens edited English subtitles for The evolution of teeth - Peter S. Ungar | ||
Michelle Mehrtens approved English subtitles for The evolution of teeth - Peter S. Ungar | ||
Michelle Mehrtens accepted English subtitles for The evolution of teeth - Peter S. Ungar | ||
Michelle Mehrtens edited English subtitles for The evolution of teeth - Peter S. Ungar | ||
Jennifer Cody edited English subtitles for The evolution of teeth - Peter S. Ungar |