Beyond the visible: What shells can tell us about our world

Narrator: Few works of architecture can match the elegance and variety of the shells of mollusks. Beauty is reason enough to appreciate and study shells for their own sake, but shells offer much more. As mollusks grow, they enlarge their shells little by little, and in doing so inscribe in their shells a detailed record of the everyday events and unusual circumstances that make their lives.”

This is a passage from a book “A Natural History of Shells” by Geerat Vermeij.

Vermeij: My name is pronounced Geerat Vermeij and I am a distinguished professor of Earth and Planetary sciences at the University of California Davis.

Narrator: The passage from his book, written in 1993, is a poetic way to describe shells that are often either overlooked or tossed into the water, but Vermeij sees in them both beauty and history. Well, to be clear Vermeij cannot see the shells… or anything else. Vermeij is blind, and has been since the age of three.

Vermeij: I’ve always had this attitude, I wanted to be completely integrated into society… The thing you really need to know is when I was very small I think even before I became formally blind I was always really attracted to natural history. My parents and my brother were basically 24 hour tour guides. They would show me everything they could and describe the rest.

Narrator: There was more to discover when in 1955, when Vermeij was 9, and the family moved from the Netherlands to United States and settled in Northern New Jersey. Fantastic things were awaiting him.

Vermeij: In fourth grade, that was about a year after I came to the U.S., I had this wonderful teacher who brought these shells from Florida and they were so spectacularly different from the ones I saw in the Netherlands that I just couldn’t get over how

beautiful these things were. Why are these shells so much fancier than the ones I was used to?

Narrator: Seashells are the exoskeletons, the hard outer sides of mollusks, a large group of shelled animals that include snails and clams. Their shells are made up of 95 percent calcium carbonate, and also a bit of protein and sugar. As the animal grows, its soft outer surface, called the mantle, releases proteins and minerals that build up the shell.

Narrator: But still, how is it possible to study shells in such detail without being able to see them? Vermeij explains his process:

Vermeij: First when I get a shell in my hand I get a really quick sense of its shape – rough or smooth. Then I start investigating with my fingers, usually the index finger. And if I need more detail, which I often do, then I might take a needle or a pin or something and look inside the opening that I can’t get my finger into.

Narrator: And some experts even believe that not seeing the shells could be an advantage.

Thompson: And in some ways this is actually a benefit because you are not tricked by the discoloration. You’ve kind of eliminated

that from your analysis.

Narrator: This is Carmi Thompson, a collection manager of the invertebrate paleontology division at the Florida Museum of Natural History.

Thomspon: For the fossil record shape and ornamentation is more important than color. So color is not really diagnostic for a lot of fossil stuff. So if a fossil is red – maybe it was red in the past but it’s more likely that some minerals in the soil leached and gave it a red color.

Vermeij: It turns out that fossils that, say, are a hundred million years old don’t look at all like modern things. And the reason they don’t is because the predators were weaker at that time.

Narrator: Vermeij reasoned that if the predators of these marine animals were weak it also meant that there was no reason for those animals to waste energy building up thick protective shells. This was the observation that starting in the 1980s, put Vermeij on the path toward the scientific theory that would eventually bring him worldwide acclaim in his field: the escalation hypothesis.

Vermeij: So that got me thinking about escalation between species and their enemies. Well, escalation obviously was going on in international relations at the time with nuclear weapons and so forth. It got me to think – how do these episodes of escalation in nature as well as in the human realm. How do they get started and how do they end?

Narrator: So we traditionally think of evolution as the survival of the fittest meaning that the animals that are most able to feed themselves and reproduce are more likely to pass on their specific genes to the offspring. For instance a hummingbird with a bill that is best suited for extracting the nectar will be the so-called fittest in the group. It will eat we, be strong and reproduce. But is that all that affects their evolution? Well the escalation hypothesis says that evolution of one species doesn’t happen in isolation from other species. Vermeij’s idea is that when we try to understand the changes in hummingbirds we also need to look at their predators and their food sources. If predators that feed on hummingbirds, such as snakes or bats, are evolving and becoming stronger, the hummingbirds have to adapt. The same goes for snails and their predators. So Vermeij’s ideas caught on, and are now part of the standard canon of paleobiology, as Carmi confirms:

Carmi: It’s taught in class as one of the big paleo theories when you take an intro to paleo class.

Vermeij: I came to realize that this whole business of evolution and ecology, it all is based ultimately on economic principles of competition, cooperation, resources and redistribution and so forth.

Narrator: Vermeij explains that an organism has only so much energy that it can use for feeding itself or for protection. For instance the thickness of a shell can protect it from predators, but it also takes time and energy to grow. So if the predator, a fish or crab, is weak, then there is no reason for a snail to grow a thicker shell. But as crabs evolve to be more apt at getting access to the snails, the snails with thicker shells will be able to survive, so a thick shell becomes a desirable trait once again. Imagine this process as a pendulum swinging back and forth, back and forth. It’s never ending, this escalating competition between predators and prey.

Vermeij: You know years later I came to realize that the longterm historical trends that we see in the history of life are repeated on a shorter timescale in the history of humans. There’s not just parallelism, there’s very fundamental, very deep parallels between these two systems for the same reason, that they are guided by the same principles.

Narrator: Vermeij observed the same escalation in humans because he was growing up during the Cold War. As the Soviet Union poured more resources into its army and weapons, American military had to evolve as well. (In 1991, however, the Soviet Union fell apart and the escalation could slow down. Now, as the pendulum swings back again it seems that the tensions between US and Russia are intensifying. So in many ways humans are no different from snails – everyone is just trying to survive and possibly dominate.

Vermeij: So I’ve always wanted to study big issues as well as the details. What can shells and their enemies for example tell us about general principles and general rules and trends, etc.? That’s been a large part of my career and continues to be

Narrator: For Scienceline, this is Polina Porotsky