In a new study published in the journal Genetics, evolutionary biologist Dominic Wright and his team looked at whether there’s a genetic connection between anxious behavior in chickens, mice and humans. Despite the compact size of the chicken genome — it’s just a third of the size of a human’s — the birds’ genes share surprising similarity to those of people. There's another reason why chickens are so great for genetic research. Because there are both wild and domesticated chickens, researchers can observe their contrasting behaviors and easily pin them to genetic differences.
Wright bred wild red junglefowl chickens with their calmer cousins, white leghorn chickens, for the experiment. After eight generations, his team was able to run open field tests — experiments during which the birds were put in a brightly-lit arena and assessed for how much time they spent cowering on the periphery instead of strutting through the room. These behavioral tests helped the team identify brave and anxious birds, then narrow down areas of the genome related to variations in anxiety. They identified 10 candidate genes in the hypothalamus, an area of the brain which helps regulate anxiety.
Those genes were also found in a large data set of mice who had gone through the same types of experiments, which gave the team hope that they’d be in anxious humans, too. But when it comes to humans, it’s harder to conduct standard tests for anxiety. “If you put a human in a novel arena with a bright light, you’d probably get remarkably similar responses,” said Wright with a laugh. “But kidnapping someone and putting them in a brightly-lit room would probably be looked upon unfavorably.” Instead of doing identical experiments on humans, the team did the next best thing. They compared genetic data from anxious chickens with data from humans with bipolar disorder, major depressive disorder, and schizophrenia.
Wright was “quite shocked” to find that the genes that affected chicken anxiety tracked to conditions, such as bipolar disorder and schizophrenia. Four of the genes tracked to similar genes within mice, and three were associated with schizophrenia or bipolar disorder in humans. The connection is perhaps not entirely surprising — over 50 percent of patients with diagnosed bipolar disorder also have a diagnosis of some kind of anxiety disorder. But the link with schizophrenia helps bring the mental illness, whose genetic links are only starting to be understood, into clearer focus for geneticists.
To Wright, the signals in both humans and mice mean that there’s more similarity between humans and animals than might meet the eye. “We always think of ourselves as being very unique,” he said, “but there seems to be a remarkable similarity in the system controlling anxiety in all different sorts of animals.”
Perhaps some mental disorders have an evolutionary basis in the same physical fear mechanisms that cause animals like chickens to freak out in the presence of predators. Next, researchers hope to take the work a step further, establishing more concrete links between the genes and using the work to paint a better picture of how genes affect behavior in all three animals.
Throwing chickens into terrifying situations in the name of human mental health seems harsh. But Wright, whose experiments were approved as ethical by a Swedish committee, says a better understanding of chicken anxiety could help chickens, too. He hopes to eventually see his study used to figure out how to breed fewer freaked-out chickens, making both scientific experiments and food production more humane. Maybe all those chicken scratches will eventually spell out a better life for all kinds of anxious animals.