Originally published April 3, 2015
For a long time we thought that language separated us from other animals, but it’s a bit more complicated than that. Chimpanzees, bonobos, gorillas, and orangutans can all learn sign language. Dogs can use body language, vocalizations, and even facial expression to communicate; and many birds can sing extraordinarily intricate songs to relay information. Even insects and plants can release chemicals that carry important information to their neighbors. So what’s unique about language?
While many animals can “speak,” or produce sounds, humans are uncommon because we can imitate sounds and mix and match them in new combinations to communicate information. This process is called “vocal learning,” and it requires using our vocal chords to imitate sounds. Neuroscientists believe we can do this because we have unique connections in our brains between higher processing areas at the front and motor areas further back that control our vocal chords; other primates—which can’t do vocal learning—don’t have these connections. But humans aren’t the only vocal learning animals, and scientists have turned their attention across 300 million years of evolution to learn more about this unique capacity.
While many birds can sing, their songs are often innate and fixed. Only three lineages possess the unique ability to learn, imitate, and modify their vocalizations based on what they hear: parrots, hummingbirds, and songbirds. Neuroscientists discovered that, like humans, these birds also have unique connections between frontal areas and motor areas controlling the vocal chords. These connections are absent in birds that can’t do vocal learning, like chickens. Both humans and vocal-learning birds that suffer damage to these connections have trouble imitating others’ vocalizations and stringing syllables together correctly. These discoveries had scientists scratching their heads: not only can distantly related birds do vocal learning, but their brains seem to be doing it in a similar way.
Before diving deeper, it’s important to appreciate the explosion in technological capacity that biological research has witnessed in the past few decades. In 1950, we didn’t know what DNA was. Since then we’ve learned that the genetic codes, or “genomes,” of both humans and birds are made of billions of nucleotides (the building blocks of DNA). We know that every cell in the body contains the same genetic code, but specific kinds of cells turn parts of the genome “on” or “off,” depending on their jobs. Think of pianos; they all have the same 88 keys, but pressing those keys in different combinations and to different degrees results in different chords. Different types of cells in our bodies “express” different combinations of genes and to different degrees; each type has its own “chord,” or its own unique gene expression fingerprint. This is even true across species: gene expression fingerprints of skin, heart, and brain cells in humans may look different from each other, but they look very similar to gene expression fingerprints of skin, heart, and brain cells in other animals.
A team of Duke neuroscientists led by Dr. Erich Jarvis recently took these ideas a bit further: are the gene expression fingerprints of “vocal-learning” brain cells unique? In other words, maybe the animal genetic code can express certain genes to create vocal-learning brain cells across species, just like skin cells or heart cells. The scientists collected tiny samples of bird brain tissue from vocal-learning brain areas in parrots, hummingbirds, and songbirds and analyzed the gene expression fingerprints for each. Next, they tapped into a huge database of gene expression fingerprints spanning the entire human brain. Like forensic detectives, they searched the database for matches. Sure enough, the strongest matches in the human brain database were regions involved in human speech and language.
So what? The idea here is that perhaps we aren’t quite as unique as we’d like to think. Scientists have known for a while that the genes guiding human body development are the same exact genes guiding body development across fishes, amphibians, reptiles, and birds. The Duke neuroscientists extended that idea to specific capacities of the human brain. The same genes that guide the development and wiring of areas involved in human vocal learning also guide the development and wiring of areas controlling vocal learning in birds.
It’s important because our language capacity is a huge part of being human, and it has indisputably shaped the course of our history. As biology advances, we will certainly continue to learn more about this unique capacity from parrots, hummingbirds, and songbirds, as well as our other vocal-learning relatives: bats, seals, elephants, and dolphins. In the meantime, the next time someone calls you “bird brain,” consider it a compliment, and take a moment to wonder what other capacities of the human brain and mind might be hidden in the animal genetic code.