vertebrates evolution social network circuits brain

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Newts aren't doing a lot of Facebook friending, and last time I checked, the cormorant had not updated its relationship status. But a new neural analysis suggests that our social networking tendencies most likely have their neural roots in some of our early vertebrate ancestors. The findings were published online May 31 in Science.

"There is ancient circuitry that appears to be involved in social behavior across all vertebrates," Hans Hofmann, an associate professor of integrative biology at the University of Texas at Austin and co-author of the new study, said in a prepared statement. Judging from the evolutionary family tree, Hofman observes, these conserved neural clusters originated at least 450 million years ago.

Hofmann and graduate student researcher Lauren O'Connell examined two parts of vertebrate brains: the so-called "social behavior network," which also includes hormones for social and sexual behavior, and the "mesolimbic reward system," which is involved in dopamine signaling that activates when we engage in pleasurable behavior. Together these two areas make up the social decision-making network, which helps humans, rainbow trout and wild boars know when to flirt or fight or form a posse. They found impressive similarities in the brains of all 88 vertebrates they studied, which included mammals, reptiles, birds, amphibians and teleost fish.

"In these key brain regions, we found remarkable conservation of gene activity across species," Hofmann said. Even though the general biological and behavioral differences between the newt and your next-door neighbor are (likely) pretty vast—making attempts to draw connections between neural structures and daily actions tricky—the genetic similarities should start to help.

The next step will be examining neural patterns at an even finer-grained scale to study the underpinnings of complex social behavior. Said Hoffman: "Now we have a framework with which we can ask whether there are molecular universals associated with social behaviors." They also noticed, however, that the locations of some key receptors and molecules were different among the groups, which suggests adaptation to specific needs in the intervening millions of years.

The researchers did not look into the brains of invertebrates, many of which are quite evolutionarily complex and move in semi-social groups—such as squid.

But for now, "On a basic level, this tells us something about where we came from," Hofmann said.

Now, whether you have enough backbone to take charge of your own social network, that's up to you.