The Same Clay

According to a Hopi creation myth, the world was once nothing but water and dry land. The Sun, in his daily travels across the dry land, noticed that he had not seen a single living being. The Sun mentioned this observation to Hurúing Wuhti of the east and Hurúing Wuhti of the west, the deities of all hard substances, and they decided they would make a little bird. Hurúing Wuhti of the east made a wren out of clay and covered it with a piece of native cloth. The deities then sang a song over it and the wren came to life. They sent the wren to fly all over the earth to search for anything living, which it did. When the wren returned and reported that no living being existed anywhere, Hurúing Wuhti of the west shaped the clay to form all kinds of birds and placed these clay birds under the native cloth. The deities sang over the clay birds, bringing them to life, and they taught each of them what sounds they should make and sent them to populate the earth. Hurúing Wuhti of the west then shaped the clay to form all kinds of other animals and placed these clay animals under the native cloth. The deities sang over the clay animals, bringing them to life, and they taught them each what sounds they should make and sent them to populate the earth. Hurúing Wuhti of the east then shaped the clay to form a woman and a man and placed these people under the native cloth. The deities brought them to life with their song, and they taught them language and sent them to populate the earth.

I like this myth; in particular because it illustrates that despite the awesome diversity of the animals on our planet, we are all made of the same stuff and share many similarities. At first glance, we may be amazed by eels that resist eating prey fish who are providing a dental cleaning service (like the one on the left),

or by snakes that eat animals larger than their own heads and toads that save themselves from the jaws of death by puffing up their bodies even larger than the snake can handle (like the snake and toad battling it out on the right),

or by the elaborate displays of male birds in their attempts to woo females (like the golden pheasant below),

or by kangaroo moms that guard their toddler-like young in their own bodies (like the one on the right).

But at closer inspection, we realize that all of these animals are facing similar challenges: All animals are driven to eat and not be eaten, to stay healthy, to make babies, and to keep their babies alive. And animals have developed behavioral tools to achieve these goals, such as ways of finding or making food and a place to live, ways to defend these things, techniques for attracting the opposite sex, and parental methods. The details are extremely diverse across animal groups, but the ultimate goals and many of the strategies are common. And amazingly, the brain systems that regulate these behaviors are common too.

In a new synthesis of decades of research spanning the field of behavioral neuroscience, researchers Lauren O’Connell and Hans Hofmann from the University of Texas at Austin show that despite our impressive diversity, mammals, birds, reptiles, amphibians and fish are all molded from the same metaphorical clay. They specifically focus on two brain systems, often called the social behavior network and the mesolimbic reward system.

The social behavior network is a term first described in mammals by neuroscientist Sarah Newman to describe several brain regions that are all sensitive to steroid hormones (such as testosterone and estrogen), connect to each other, and are involved in many types of social behavior (including aggression, sexual behavior and parental behavior). We now know that reptiles, birds and fish also have brain areas that are similar in how they connect to one another and what neurotransmitters and other neurochemicals they use. More importantly, these brain areas seem to relate to the same types of social behaviors in similar ways.

The mesolimbic reward system is primarily a circuit of neurons that interact using the neurotransmitter dopamine. This neural circuit is central to how the brain controls motivation and a sense of desire and reward. This system is also involved in evaluating the importance of what is being perceived in order to behave accordingly. The mesolimbic reward system has been studied most in mammals, but birds, reptiles and fish are known to seek pleasure too and similar brain structures are likely involved.

This figure from O'Connell and Hofmann's paper in the Journal of Comparative Neurology shows corresponding brain regions in mammals, birds, reptiles, amphibians and fish. The images are shown as cross-sections of the brains as if we are looking directly at the front of the animals.

O’Connell and Hofmann show that the social behavior network and mesolimbic reward system work together as a single social decision-making system. For example, if one animal comes onto the territory of another animal, the brain areas of these two systems will work together to determine if the interloper should be fought, courted, nurtured, or eaten. (Imagine the consequences of getting this decision wrong!) Although mammals, birds, reptiles, amphibians and fish have very different lifestyles and brains, most of the brain areas of this social decision-making system are present, identifiable, and most importantly, play similar roles in regulating social behavior across all these animal groups. In the end, we’re not all so different after all.

Want to know more? Check these out:
1. O’Connell, L.A. and Hofmann, H.A. (2011). The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis. The Journal of Comparative Neurology, 519(18), 3599-3639.
2. O’Connell, L.A. and Hofmann, H.A. (2011). Genes, hormones, and circuits: An integrative approachto study the evolution of social behavior. Frontiers in Neuroendocrinology, 32, 320-335.
3. Native American legends at FirstPeople.us