Dolphin Brains

Introduction

Dolphins and other marine mammals have pretty big brains compared to the size of their bodies. That’s one indication of high intelligence, and anyone who has seen them perform at an aquarium or zoo can attest to that fact. Science reporter Bob Hirshon introduces us to one scientist who’s trying to find out how dolphins got so brainy.

Podcast

Dolphin Brains

Transcript

Under-the-sea intelligence. I'm Bob Hirshon and this is Science Update.

On the TV show “Flipper,” the dolphin always managed to outsmart the bad guys.

Lori Marino is a psychologist at Emory University and the Center for Behavioral Neuroscience. And she says in the real world, dolphins aren’t quite as smart as humans. But they are as smart as other primates, despite having very different brains.

Marino:
If you look at the dolphin brain, it is organized in a completely different way from the primate brain. Yet, they’re able to accomplish the same sorts of cognitive and behavioral abilities. So the question is, how are they doing the same thing with a different brain?

To find out, Marino and her colleagues are looking at how the dolphin brain evolved. They’re taking CT scans of dolphin skulls and the fossil skulls of their ancient relatives. The goal is to create virtual models of the dolphin brain throughout history.

Marino:
And we hope that when we finish this project, we’ll be able to have a good idea of how brain size and to some extent, shape, changed throughout the course of cetacean evolution.

She says comparing dolphins to primates can reveal how each evolved the intelligence needed to thrive in its own environment. For The American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

If you want to build a house, you can use brick, stone, wood, or any number of other materials. If you want to get from New York to Boston, you can fly, drive, take a train, sail, or ride a bike. If you want to re-heat a pizza, you can put it in the oven or the microwave. In other words, in life, there are a lot of different ways to get the same result.

This seems to be the case with dolphin and primate brains, which seem to be able to accomplish equally impressive things using very different structures. It's difficult to compare the intelligence of dolphins and apes, or even to define what "intelligence" means, and it doesn't help that far less time and energy has been devoted to studying dolphins compared with our primate kin. Still, some research indicates that dolphins can solve problems, communicate, and process information in ways that are as sophisticated as our closest land-dwelling animal relatives.

This is true despite the fact that the dolphin brain is very different from the primate brain. For example, human and primate brains are organized on a front-to-back axis, with the frontal lobes being the center of our most advanced thinking and processing. Dolphin brains don't quite follow this organizational structure. What's more, in the outer part of the brain called the cortex, human and primates have many different kinds of cells, while dolphins have repeating patterns of only a few kinds of cells. Dolphin brains also function differently in many ways - for example, only one half of their brain "sleeps" at any given time, which probably prevents them from drowning.

To shed light on the mystery of how dolphins have achieved such intellectual prowess, Marino and her colleagues are looking back in time to see how their brains evolved. They're tracing the development of the dolphin skull, and how the space for the brain within it changed in size and shape over time. To do this, they use a medical technique called a CT scan, which allows you to see inside the skull. It's thought that in general, increases in brain size relative to an animal's body reflect increases in brain sophistication and intellectual capacity - a process called encephalization. Marino says that the ancestors of dolphins appear to have undergone a history of encephalization that mirrors the primate and human lines. Getting a clearer picture of how the dolphin brain developed may help scientists understand how the evolution of intelligence in dolphins parallels and contrasts with our own story.

Now try and answer these questions:

1. Why is dolphin intelligence interesting to researchers?
2. What are some differences between dolphin and primate brains?
3. What do the CT scans of the ancient dolphin skulls tell us about the development of the dolphin brain?
4. Aside from intelligence, can you think of a trait or a skill in the animal kingdom that is achieved in two very different ways by two different animals?
5. What are some ways that intelligence can be measured in animals? How would you define "intelligence?" Do you think it's possible to compare the intelligence of two different species? Why or why not?

Going Further

You can see some pictures of an actual dolphin brain from the University of Wisconsin and Michigan State Comparative Mammalian Brain Collections website. How do they compare to human brains?

To further explore the connection between brain and body size try the following resources at the Serendip website. At Compare Brain and Body Sizes you can find out what might happen if all animals were the same size. The Question of Intelligence explores the relationship of brain size and intelligence.