{"id":16797,"date":"2019-09-08T07:04:43","date_gmt":"2019-09-08T07:04:43","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=16797"},"modified":"2020-06-09T12:41:42","modified_gmt":"2020-06-09T12:41:42","slug":"comparing-primate-vocalizations","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/comparing-primate-vocalizations\/","title":{"rendered":"Comparing primate vocalizations"},"content":{"rendered":"\n
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Study shows Old World monkeys combine items in speech \u2014 but only two and never more, unlike humans.<\/strong><\/p>\n\n\n\n

The utterances of Old World monkeys, some of our primate cousins, may be more sophisticated than previously realized \u2014 but even so, they display constraints that reinforce the singularity of human language, according to a new study co-authored by an MIT linguist.<\/p>\n\n\n\n

The study reinterprets evidence about primate language and concludes that Old World monkeys can combine two items in a language sequence. And yet, their ability to combine items together seems to stop at two. The monkeys are not able to recombine language items in the same open-ended manner as humans, whose languages generate an infinite variety of sequences.<\/p>\n\n\n\n

\u201cWe are saying the two systems are fundamentally different,\u201d says Shigeru Miyagawa, an MIT linguist and co-author of a new paper detailing the study\u2019s findings.<\/p>\n\n\n\n

That might seem apparent. But the study\u2019s precise claim \u2014 that even if other primates can combine terms, they cannot do so in the way humans do \u2014 emphasizes the profound gulf in cognitive ability between humans and some of our closest relatives.<\/p>\n\n\n\n

\u201cIf what we\u2019re saying in this paper is right, there\u2019s a big break between two [items in a sentence], and [the potential for] infinity,\u201d Miyagawa adds. \u201cThere is no three, there is no four, there is no five. Two and infinity. And that is the break between a nonhuman primate and human primates.\u201d<\/p>\n\n\n\n

The paper, \u201cSystems underlying human and Old World monkey communications: One, two, or infinite,\u201d is published today in the journal\u00a0Frontiers in Psychology<\/em>. The authors are Miyagawa, who is a professor of linguistics at MIT; and Esther Clarke, an expert in primate vocalization who is a member of the Behavior, Ecology, and Evolution Research (BEER) Center at Durham University in the U.K.<\/p>\n\n\n\n

To conduct the study, Miyagawa and Clarke re-evaluated recordings of Old World monkeys, a family of primates with over 100 species, including baboons, macaques, and the probiscis monkey.<\/p>\n\n\n\n

The language of some of these species has been studied fairly extensively. Research starting in the 1960s, for example, established that vervet monkeys have specific calls when they see leopards, eagles, and snakes, all of which requires different kinds of evasive action. Similarly, tamarin monkeys have one alarm call to warn of aerial predators and one to warn of ground-based predators.<\/p>\n\n\n\n

In other cases, though, Old World monkeys seem capable of combining calls to create new messages. The putty-nosed monkey of West Africa, for example, has a general alarm call, which scientists call \u201cpyow,\u201d and a specific alarm call warning of eagles, which is \u201chack.\u201d Sometimes these monkeys combine them in \u201cpyow-hack\u201d sequences of varying length, a third message that is used to spur group movement.<\/p>\n\n\n\n

However, even these latter \u201cpyow-hack\u201d sequences start with \u201cpyow\u201d and end with \u201chack\u201d; the terms are never alternated. Although these sequences vary in length and consequently can sound a bit different from each other, Miyagawa and Clarke break with some other analysts and think there is no \u201ccombinatorial operation\u201d at work with putty-nosed monkey language, unlike the process through which humans rearrange terms. It is only the length of the \u201cpyow-hack\u201d sequence that indicates how far the monkeys will relocate.<\/p>\n\n\n\n

\u201cThe putty-nose monkey\u2019s expression is complex, but the important thing is the overall length, which predicts behavior and predicts how far they travel,\u201d Miyagawa says. \u201cThey start with \u2018pyow\u2019 and end up with \u2018hack.\u2019 They never go back to \u2018pyow.\u2019 Never.\u201d<\/p>\n\n\n\n

As a result, Miyagawa adds, \u201cYes, those calls are made up of two items. Looking at the data very carefully it is apparent. The other thing that is apparent is that they cannot combine more than two things. We decided there is a whole different system here,\u201d compared to human language.<\/p>\n\n\n\n

Similarly, Campbell\u2019s monkey, also of West Africa, deploys calls that might be interpreted as evidence of human-style combination of language items, but which Miyagawa and Clarke believe are actually a simpler system. The monkeys make sounds rendered as \u201chok,\u201d for an eagle alarm, and \u201ckrak,\u201d for a leopard alarm. To each, they add an \u201c-oo\u201d suffix to turn those utterances into generalized aerial alarms and land alarms.<\/p>\n\n\n\n

However, that does not mean the Campbell\u2019s monkey has developed a suffix as a kind of linguistic building block that could be part of a more open-ended, larger system of speech, the researchers conclude. Instead, its use is restricted to a small set of fixed utterances, none of which have more than two basic items in them.<\/p>\n\n\n\n

\u201cIt\u2019s not the human system,\u201d Miyagawa says. In the paper, Miyagawa and Clarke contend that the monkeys\u2019 ability to combine these terms means they are merely deploying a \u201cdual-compartment frame\u201d which lacks the capacity for greater complexity.<\/p>\n\n\n\n

Miyagawa also notes that when the Old World monkeys speak, they seem to use a part of the brain known as the frontal operculum. Human language is heavily associated with Broca\u2019s area, a part of the brain that seems to support more complex operations.<\/p>\n\n\n\n

If the interpretation of Old World monkey language that Miyagawa and Clarke put forward here holds up, then humans\u2019 ability to harness Broca\u2019s area for language may specifically have enabled them to recombine language elements as other primates cannot \u2014 by enabling us to link more than two items together in speech.<\/p>\n\n\n\n

\u201cIt seems like a huge leap,\u201d Miyagawa says. \u201cBut it may have been a tiny [physiological] change that turned into this huge leap.\u201d<\/p>\n\n\n\n

As Miyagawa acknowledges, the new findings are interpretative, and the evolutionary history of human language acquisition is necessarily uncertain in many regards. His own operating conception of how humans combine language elements follows strongly from Noam Chomsky\u2019s idea that we use a system called \u201cMerge,\u201d which contains principles that not all linguists accept.<\/p>\n\n\n\n

Still, Miyagawa suggests, further analysis of the differences between human language and the language of other primates can help us better grasp how our unique language skills evolved, perhaps 100,000 years ago.<\/p>\n\n\n\n

\u201cThere\u2019s been all this effort to teach monkeys human language that didn\u2019t succeed,\u201d Miyagawa notes. \u201cBut that doesn\u2019t mean we can\u2019t learn from them.\u201d<\/p>\n
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