The Tooth of Time

One of the main reasons evolution can be difficult to grasp, or even accept, is the time scales involved.

Biological evolution does usually not occur right in front of our eyes (other than in laboratory experiments), but happens over many generations. Most people, especially in increasingly urbanized environments largely disconnected from the natural world, will never get to see any significant evolutionary change during their own lifetime.

One place where evolution can be appreciated to its full extent, though, is a natural history museum. These museums explicitly visualize the evolutionary changes that have taken place during the course of life’s history on Earth, from its very beginning almost 4 billion years ago to currently existing species, including humans.

A great example is the natural history museum in Berlin (pictured above), where I once took a backstage tour. Our private and very knowledgeable guide Brandon Kilbourne turned out to be a walking encyclopedia on the evolution of mammals. His specific focus on this tour was the evolution of mammalian skulls and teeth.

He started with a display of such skulls and teeth spread out across a long table. With each skull he picked up, Brandon would first let us guess the animal it came from. Then he explained something about the specific adaptations to the kind of environment that animal lives in, and the type of food it eats.

One of the main functions of a skull, next to providing a protective case for the brain, is to generate biting force. The lower jaw is connected to the rest of the skull by strong muscles and tendons, providing the right configuration to bite or chew. As a consequence, the particular shape of an animal’s skull, including its teeth, can often reveal something about its diet.

The skull of a killer whale

When it came to one of the largest skulls on the table, with a long snout and big pointy teeth, of course we all thought it was from a crocodile. But given that it had to be a mammal, the right answer turned out to be a killer whale (or orca). This is a nice example of convergent evolution, i.e., a similar kind of adaptation to a similar type of lifestyle and diet, but in very different evolutionary lineages (in this case reptilians and mammals).

But once teeth and the right skull structures for biting had appeared, evolution didn’t stop there. In fact, as Brandon showed us, mammals have evolved an amazing range of tooth structures to perform such various tasks as chewing, cutting, grinding, digging, fighting, filtering, and even sensing.

In the image of the orca skull above, you can also see part of a narwhal tusk. This tusk is actually an elongated tooth that can grow up to 10 feet (3m) long. It is hollow, and contains long nerves connected to the narwhal’s brain. It uses these nerves to sense chemical and temperature changes in the ocean water. Quite an impressive evolutionary adaptation from what used to be a simple tooth!

Out of an Alien movie?

Moving on to another part of the mammal room, Brandon showed us a closet full of seal skulls that looked like they came straight out of an Alien movie.

A closet full of seal skulls

Seals have adapted in such a way that their skulls are both hydrodynamic (for fast swimming) as well as provide a strong bite (to catch and eat fish). This is a good example of how evolution often has to deal with conflicting constraints. A powerful bite requires a big and bulky skull, while a hydrodynamic skull should be small and slim. Somehow seals have evolved a compromise between these conflicting constraints that allows them to perform both functions simultaneously, and quite well.

After our private backstage tour was finished, we still had time to visit some of the main museum exhibits.

T. rex, always a crowd favorite

A favorite part of any natural history museum is always the dinosaur collection. It so happened that a large, and mostly original, T. rex skeleton was on display in Berlin, on loan from the United States. The full skeleton is 40 feet (12m) in length and 13 feet (4m) in height. It was discovered in 2010 in Montana, and is one of the best preserved in the world. Since T. rex didn’t have a very large brain to protect (relative to its body size, unlike mammals), its large skull and teeth have obviously mostly adapted to kill, rip, and tear its prey. A very impressive sight indeed.

So, if you really want to see evolution “happening before your eyes,” visit a natural history museum.

Biological evolution generally happens over large time scales, and many species have come and gone during life’s long history. But luckily our natural history museums provide “a forted residence ’gainst the tooth of time, and razure of oblivion.”

Wim Hordijk (@WanderingWim) describes himself as “a computer scientist by training, an evolutionist by historical accident, an academic against better judgment, and a professional wanderer by choice.” He is most interested in the interface of computation and biology, especially focusing on emergence, evolution, and origin of life.

(Main image: Museum für Naturkunde, Berlin; all other images: © Wim Hordijk.)