Passage V

The Evolution of Vocal Learning

[1]

Scientists distinguish vocal learning, the ability to remember and reproduce sounds after hearing them from auditory learning, the ability to make associations with certain sounds. For example, dogs' ability to recognize a command such as "sit" is an example of auditory learning because while dogs can learn to identify and respond to the sound, they can't imitate the sound. Dogs do of course vocalize, they bark. However, dogs' ability to bark is a genetically innate vocalization. That is, a dog doesn't learn to bark but, rather, are born knowing how. [A]

[2]

Only humans, bats, cetaceans (whales and dolphins), seals, elephants, and three groups of birds—parrots, hummingbirds, and songbirds—are capable of vocal learning. [B] Even though these groups of animals are only distantly related, they have similarities in brain structure that accounts for the shared vocal learning ability. [C] Neurobiologist Erich Jarvis, who studies the vocal learning process in birds, has a theory about why so little species' possess this ability.(67)

[3]

Jarvis suspects vocal learners share a common ancestor that existed before the avian/mammalian evolutionary split. [D] Vocal learning was once a common ability, it was, however, eliminated in most species by natural selection. Because vocal learners produce a wide range of sounds, or varied syntax, Jarvis surmises that such creatures were in more danger from predators than were innate vocalizers, whose less-varied sounds blend more easily with background noise. The species that have retained vocal learning ability are rare exceptions. They either have few natural predators (71) or have effective escape methods (as in the case of birds).

[4]

Similarly, vocal learners may have developed the ability in a state of independence of one another. Jarvis concedes that he has yet to identify a common ancestor. The similarities in vocal learners' brain structure's, however, make it difficult for Jarvis to dismiss the theory.