Except for diverse cartoon characters, the Geico Gecko and Mr. Ed, animals can't speak. Yet they have a lot to say to scientists trying to figure out the origins of man language.

Speaking isn't the only artery for language. After all, linguistic messaging can be transmitted by manus signals. Or handwriting. Or texting. Simply speech is the original and most basic mode of human being communication. And so understanding its origins ought to generate deeper comprehension of language more than generally. And a first stride toward that understanding, cognitive scientist W. Tecumseh Fitch believes, is realizing that key aspects of vocal linguistic communication are not, every bit traditionally contended, limited to humans.

He's not talking about a Tv set-show horse, of course, or animated narrators of insurance advertisements. Fitch's point is that many creatures from the real-world animate being kingdom offer clues well-nigh how the capacity for speech came to be.

It'south true that humans, and humans alone, evolved the complex set of vocalization, hearing and encephalon-processing skills enabling full-scale sophisticated vocal advice. Yet animals can make complicated sounds; parrots tin can mimic homo oral communication and cats tin conspicuously convey that information technology's time for a treat. Many animals possess an acute sense of hearing and are able to distinguish random noises from intentional advice. And then fifty-fifty though merely humans possess the complete linguistic bundle, the components of linguistic communication ability "take very deep evolutionary roots," says Fitch, of the University of Vienna. In fact, he suggests, just a handful of changes in the advice repertoire of humankind'southward ancestors endowed people with the total faculty of language.

Much of the physiological appliance for hearing and speaking is constitute in all land-habitation vertebrates — the tetrapods — including mammals, birds, amphibians and reptiles. "Humans share a significant proportion of our basic mechanism of hearing and vocal product with other tetrapods," Fitch writes in the Annual Review of Linguistics.

Life-forms occupying numerous branches of the tree of life possess anatomical tools for producing and perceiving song advice. Where human ability exceeds our predecessors, Fitch says, is the composure of the brain circuitry adapted to the uniquely human capacity for complex linguistic expression.

Historically, language experts accept proposed anatomical explanations for human being's special language facility. Merely as the opposable pollex permitted tool use, some regime theorized that the lower location of the vocalism box in the vocal tract enabled the articulation of meaningful sounds. Or the homo hearing apparatus, encompassing hair cells and eardrum and three little bones, provided the discerning ear capable of interpreting nuanced vocalizations. But in reviewing the scientific literature, Fitch finds that spoken language's structural subcomponents, used for producing vocalizations and perceiving patterns in those sounds, accept appeared in multiple organisms over evolutionary time.

An anatomical view of the human head and throat highlight some key structures involved in speech, including the larynx, or voice box, vocal chords (folds), windpipe, tongue and lips.

Amidst primates, simply humans tin learn to produce novel vocal sounds, but that deviation isn't explained past anatomy — the basic structure of the human voice box and song tract is similar to that institute in other mammals. Cartilage and musculus within the vocal folds of the phonation box (or larynx) give mammals better control over vocalizing than other vertebrates. Fleshy tongues and lips are besides mammalian features that aid in speech production.

CREDIT: CLAUS LUNAU / Science SOURCE

The ear's sensory hair cells, which convert sound vibrations into nervus impulses, get back as far as jellyfish, for instance. Genes instrumental to producing the pilus cells are similar in insects and humans.

In some cases, a particular trait evolved independently in different lineages. But often a trait evolved once and so was passed down through a long line of descendants. Such "homologous" traits "provide the equivalent of a fourth dimension auto assuasive us to reconstruct an evolutionary sequence of bequeathed forms," Fitch notes. Independently arising traits, on the other paw, provide data points helpful for testing evolutionary hypotheses. Combined, the homologous inherited traits and the independent analogous traits accept produced deep and novel insight into spoken communication'due south evolutionary origins.

Among the tetrapods, mammals evolved much more sensitive hearing, able to cope with a wider range of frequencies and therefore more able to procedure nuances of vocalizations. Humankind'south primate ancestors, for instance, possessed highly capable hearing power. "At that place is nothing about the human ear that is strikingly different from that of other primates," Fitch writes. "Our peripheral hearing apparatus was in place, in our primate ancestors, in essentially mod form long before we evolved the capacity for speech."

But perhaps successful speech perception required "vocal tract normalization" — the ability to recognize the same words spoken past different voices (such as a child versus an sometime homo). Humans are not, all the same, lonely in that ability, either. Zebra finches trained to recognize vowels when listening to a male vocalisation can notwithstanding make the distinction when the speaker is a woman.

Peradventure the primal human-only skill is the ability to figure out which of the globe's many complex sounds are vocal efforts to communicate. In the part of the human brain that responds to sounds (the auditory cortex in the temporal lobe), some of the circuitry is specialized for voices as opposed to other sounds. But such voice-specific circuitry besides exists in nonhuman primates and perhaps even dogs. "The data lead to the conclusion that the primate auditory system had already evolved to a 'speech-set up' level of sophistication long earlier spoken language evolved in our species," Fitch writes.

If hearing skill isn't the source of human linguistic ability, maybe the human being-only aptitude for spoken language lies in the power to produce information technology. Nonhuman primates can make song noises, but unlike in Planet of the Apes movies cannot articulate the nuanced sounds of oral communication. But it's not obvious why not, every bit the basic blueprint for the human vocal tract has been effectually for 70 million years and is shared past most mammals. Even the lower position of the voice box — the descended larynx — is not exclusively human. And that anatomical aligning isn't necessary for complicated phonation, anyway. Experiments accept shown that some primates have vocal tracts capable of ample vocal agility.

"An unmodified primate or mammal vocal tract would be perfectly adequate to produce intelligible oral communication," Fitch writes.

Evolutionary tree showing the descent of major groups, called clades, of human relatives from a common ancestor. Clades listed include (from bottom to top) eukaryotes, vertebrates, tetrapods, amniotes, hominids and hominins. Scientists have used such groupings for insight into the evolution of spoken language in humans, a trait not shared by any other animal.

By studying clades — groups of species related by a common lineage of descent (simplified tree shown here) — scientists can compile clues nearly the evolution of speech. Many aspects of human speech and hearing, for instance, rely on features found in all tetrapods, a clade that includes mammals, reptiles and amphibians. Of particular interest are homologous and analogous traits. All mammal species, for case, accept three middle-ear basic, a homologous trait inherited from a mutual ancestor. Neural connections betwixt parts of songbird brains important for vocalization may be analogous to neural connections between speech-related parts of human being brains; those connections evolved independently in different lineages but may both exist of import for speech production.

Also all that, parrots and many other bird species, some bats and even elephants can mimic song sounds. So humans' distinctive speech can't depend solely on vocal production power. Considering all the testify, the vocal and auditory skills of various animals tell a tale of multiple preludes to the human speech story. That tale reveals that humans acquired oral communication not via anatomical innovation for vocalizing and hearing, but by novel neural connections that control the anatomical hardware.

After all, voice communication requires more than producing and perceiving sounds. A speaker's encephalon must determine what sounds to produce and result instructions for producing them to the torso's song apparatus. And a listener's brain must be able to decode auditory signals it receives and so issue commands for a vocal response. People are skillful at producing sounds in response to other sounds — it'due south why you can repeat a word out loud after the first fourth dimension you hear it.

Such controlled phonation of a word is different from but making racket. Most animals possess neural circuitry for producing "innate" vocalizations: Dogs bawl, squirrels chatter and seagulls squawk. Even humans have their own innate vocalizations, including crying, laughter and screams. Just amidst primates, but humans accept the "capacity to produce novel, learned vocalizations beyond the innate call repertoire," Fitch notes.

Today the ascendant hypothesis explaining that ability is the presence of special connections between brain regions involved in controlling oral communication and hearing. Innate calls — in humans and all other mammals — are initiated by direct signals from the brain stem. Indirect messaging from the cortex (the encephalon's more advanced outer layer) enables voluntary suppression or production of innate calls. Different other animals, humans possess direct connections between nerve cells in the cortex and the nerve cells that command the muscles operating the larynx. Some apes and monkeys have straight connections from cortex to the muscles controlling the lips and natural language, only non to the muscles decision-making the larynx. (Circuitry connecting the auditory cortex to the motor cortex also seem more than extensively developed in humans.)

Evidence supporting the view that such direct neural connections explain man speech comes from other species that can "talk," such equally parrots and songbirds that can learn novel vocalizations. These species exercise take direct neural connections to their vocalisation-generating apparatus, while non-vocal learning birds don't.

Underlying the evolution of the brain circuitry responsible for homo speech skill are genetic modifications that remain largely mysterious.

Diagram shows simplified views of human brain. One highlights the direct neural connection linking the motor cortex to the muscles in the voice box. The second shows nerve connections, shared with primates, between Broca's region and the auditory cortex. It also shows additional connections between these brain areas running through the parietal cortex and found only in humans.

Among primates, it seems that only humans possess direct connections (shown at left) from the office of the brain that controls motion to nerve cells in the brain stem (black dot) that control the larynx muscles responsible for vocalizing sounds. Shown at right: Other primates too every bit humans possess nerve connections (dashed line) betwixt brain areas involved in language (Broca's region) and hearing (auditory cortex). Just human brains have more fully developed boosted connectedness pathways (blue and red lines) that researchers hypothesize play key roles in producing and processing spoken communication.

"The genetic underpinnings of … [neural] connections involved in human vocal command are near unknown," writes Fitch. Simply genetic analyses of aboriginal organisms and testing Deoxyribonucleic acid found in fossils is an emerging research field. "Thus, genetic data possibly provide the most promising and exciting empirical pathway for time to come research on the biology and evolution of speech."

Equally Fitch notes, speech is non the whole story of man linguistic communication. Song communication is a central feature, only language encompasses much more, as linguist and neuropsychologist Angela Friederici pointed out at a recent meeting of the Society for Neuroscience.

"Language is more voice communication," said Friederici, director of the Max Planck Institute for Homo Cognitive and Brain Sciences, in Leipzig, Germany. "Speech … uses a limited set of vowels and consonants to class words. Language, notwithstanding, is a system consisting of words … and a fix of rules called grammar or syntax to form phrases and sentences."

Nonhuman primates can learn the meaning of private words, she notes, but aren't capable of combining words into meaningful sequences of any substantial length. That ability also depends on circuitry connecting different parts of the brain, electric current enquiry past Friederici, collaborators and other scientists is now showing.

Understanding that circuitry depends on comparing the cellular architecture and nerve fiber tracts of the homo brain with the brain of animals with bottom linguistic power. So in a manner, scientists may be able to ask animals for clues not but to the evolution of speech communication, merely to language skills more than mostly equally well. Sort of like going straight to the source and request the horse.