This report is the beginnings of an attempt at a comparative approach to bilingualism, in the style of Fitch(2005). Bilingualism is difficult to define, but by asking whether there is evidence for this capacity in non-human species, it's hoped that this question is made clearer.
FLA and FLB
This research project takes an evolutionary approach to Bilingualism. One of the most difficult problems faced so far is identifying the role of bilingualism in the cultural evolution of language. Is it a product or a catalyst? Firstly, I'm not sure whether this has been considered to any great extent. However, I suggest that the implicit assumption in the vast majority of work in both the areas of Bilingualism and Language Evolution has been that bilingualism is a product of the merging of homogenous language communities. This report explicitly asks the question: Which came first - Language or Bilingualism? That is, did the capacity for bilingualism develop from a pressure to learn multiple existing languages or was it a capacity which existed before human languages were established and influenced their arrival?
The latter hypothesis seems to be non-sensical. How can individuals have the ability to learn more than one language when there are no languages to be learned? Here, I'd like to make a distinction between two kinds of bilingualism, following the approach of Hauser Chomsky Fitch (2002). Bilingualism in the narrow sense means the ability to learn several human languages. This is obviously a human-only trait. Bilingualism in the broad sense refers to the general capacity to acquire more than one signalling system. Depending on how one defines signalling systems, this capacity may be shared with many other animals, both closely and distantly related. Of course, defining what constitutes a single signalling system is difficult, let alone defining language or bilingualism. However, it's hoped that the approach taken in this paper will help towards this goal by considering the features of the phenomenon we wish to define.
Before considering this possibility, the comparative approach to language evolution is presented. Fitch (2005 and others) approaches the study of the evolution of language by considering what elements contribute towards the `Faculty of Language'. In the broad sense of the term, this covers all the prerequisite elements that are required for linguistic communication. This involves cognitive capacities such as acoustic string segmentation and semantic processing, but also much more basic features such as memory. That is, features of the Faculty of Language in the broad sense (FLB) are found in humans and animals. The narrow sense of the term (FLN) refers to those capacities which are involved in language alone. There is much more debate about what these elements are. Recursive processing has been suggested as one example.
The comparative approach has been used to answer the question of what belongs to FLN and to FLB. Animals have been shown to be capable of a number of processes required for language, including categorical perception of speech sounds (Kuhl & Miller, 2978) and Mutual Exclusivity (Juliane & Kaminski, 2004). From studies of divergent and convergent evolution of these traits, some important features have been identified. For example, many species which exhibit vocal learning have direct neural connections between the brain and vocal motors, while non-vocal learners do not (see Doupe, 1999).
This report suggests that this approach should be adopted for the study of Bilingualism. Such an approach would seek to answer whether bilingualism is a uniquely human capacity. If it turns out that other animals also have this capacity, then the role of bilingualism in the evolution of language can be re-assessed.
However, there is a large initial problem. Even FLB only consists of capacities that are required for language. Bilingualism in the broad sense, however, is not required in order to speak a language. This problem may be due to the individual-level bias to the idea of the 'Faculty of Language'. Its primary aim is to describe capacities that an individual organism requires, rather than a community. Therefore, bilingualism may not be part of the FLB, and simply a product of cultural interaction. However, the comparative approach can help verify this hypothesis if social animals exhibit the capacity for bilingualism. That is, if bilingualism comes from cultural interaction alone, there should be no non-social animals which have the capacity for it.
Bilingualism in Bengalese Finches
If other species exhibit bilingualism, then this is evidence that bilingualism developed before human language. Takahasi & Okanoya (2010) study the vocal learning patterns of the Bengalese Finch. These are a domesticated breed descended from wild White Backed Munia. The Bengalese Finch exhibits very complex song patterns in comparison to the White Backed Munia.
Takahasi & Okanoya (2010) carry out a cross-fostering experiment where Munias are brought up by Finches, and Finches are brought up by Munias. The Munias tended to have a stronger preference for copying Munia songs, while the Finches are not so disposed towards their own strain's song. That is, Finches have more flexibility in learning. It is hypothesised that this is because there is a pressure on Munias to identify their own strain in the wild where there are mixed flocks, while this pressure has been masked for Finches by domestication and isolation.
However, is this really `Bilingualism'? The problem is that, although there is flexibility in the sources of acquisition, the birds do not have the same flexibility in production. That is, as I understand it, they still develop only one song (i.e. they can't sing elements of A and B's songs in the morning, then elements of C and D's songs in the evening). Furthermore, the idea of 'comprehension' is more difficult to apply, since there is no semantics.
It has been suggested that Bengalese Finches have developed song complexity as a sexual display (Okanoya, 2004). Following from this, Soma et al. (2009) find that chicks select tutors based on their song complexity. Also, Okanoya (2010) presents some evidence to suggest that Benglaese Finches learn from many tutors. That is, they splice whole segments of songs from many other individuals to create their own song. In this sense, learning from multiple tutors increases the complexity of the song and so increases the attractiveness and fitness of the individual.
The ability to learn syntactic sequences from many tutors has apparently occurred in a system with no semantics. This may suggest that bilingualism at the syntactic level emerged before bilingualism at the lexical level, opposite to the order implicitly assumed by many. One big advantage of cultural evolution is that individuals can inherit information from multiple sources, whereas there are a limited number of biological parents. This is the core of what I mean by Bilingualism being a preadaptation for language: part of the acquisition of human languages requires the flexibility afforded by bilingualism.
Counter Arguments
This phenomenon in Bengalese Finches is interesting, but may not help with our question. Although the complexity of the system has increased due to a change in the environment (domestication), whether this was initially enabled by learning from multiple tutors is not clear.
Also, Okanoya has shown that vocal learners who co-inhabit areas with other species of vocal learners have less complex song. That is, song complexity does not help species identification. Therefore, if the capacity for bilingualism developed in humans before language, it's likely that there was little pressure on vocal cues for species identification.
Inter-species semantic communication
Many species also communicate vocally with other species. Vervet monkeys respond to the territorial and alarm calls of superb starlings (Seyfarth Cheney, 1990). Ring-tailed lemurs respond to the alarm calls of Verreaux's sifakas (Oda Masataka, 1996). However, captive ring-tailed lemurs who had never heard the sifakas' alarm calls also responded appropriately to playbacks. Oda and Masataka argue that they are therefore responding to shared acoustic features rather than to an associated meaning. Although in most examples of inter-species communication do not involve the transference of 'concepts', some examples do show evidence for this.
Zuberbuhler (2000) studied communication between Diana monkeys and Campbell's monkeys. Diana monkeys respond appropriately to Campbell's monkeys' alarm calls for leopards and eagles. Furthermore, their responses suggest they are attending to the meaning rather than the acoustic signal. If a Diana monkey hears a leopard or a leopard alarm call, it calls out loudly, but if it hears a second leopard or leopard alarm, it is quieter, presumably because of the risk of predation (the same is true of eagle alarms). Diana monkeys were primed with Campbell alarms for either leopards or eagles then probed with either eagle or leopard sounds (growls and shrieks). They responded loudly to each combination, apart from where the Campbell alarm corresponded to the predator type (e.g. Campbell leopard alarm followed by a leopard sound). In these cases, the Diana monkeys were quieter, suggesting that they thought the predator was already present.
Zuberbuhler concludes that "Diana monkeys can flexibly use and assess information derived from the communication of other species" and that "semantic understanding can be based on arbitrary signals, as it is the
case for word meaning" (Zuberbuhler, 2000, p. 717). Diana monkeys seem to understand the same concept from two different calls. I argue that this is bilingualism in the broad sense at the lexical-like level.
Again, Diana Monkeys are limited by their physiology in terms of production of the Campbell's alarms. However, the information transfer from Campbell's monkeys to Diana monkeys is not 'communication' as defined by MaynardSmith Harper, 2003) (also see Scott-Phillips, 2008). That is, although the Campbell's calls affect the behaviour of the Diana monkeys, they did not evolve to do this (they are cues, not signals). Therefore, I'd like to suggest that the origins of the capacity for bilingualism originates in the evolution from cues to signals.
However, these responses may not be learned. Furthermore, there is no current evidence to suggest that Campbell's reciprocate in their comprehension of Diana Monkey's calls. The latter issue is discussed by Magrath (2009) who study the alarm call responses of 3 ecologically distinct avian species and find that responses may be reciprocal, but not necessarily symmetrical. Different species reacted to each other's alarm calls in proportion to the 'reliability' of the call as a cue to one of the listener's predators. That is, not all predators of species A are predators of species B, so the A's alarms are not always reliable for species B, and species B responds appropriately. In Magrath (2009)'s study, some species responded in the same way to three different calls. Again, this is evidence for bilingualism in the broad sense.
This raises an interesting question of 'reliability' or 'relevance' (as in Relevance theory, Sperber Wilson, 1995) in animal communications. Much of animal communication is limited to and grounded in information relevant to shared survival interests, that is, food, predators and mating. Humans are capable of communicating about topics beyond their immediate survival needs. This difference possibly requires the of 'ungrounding' of signals from the domains in which they evolved (see the next section).
Bilingualism's impact on FLB
Although bilingualism may not be necessary for the acquisition of language, and so could arguably not be part of FLN, learning two languages does seem to have a qualitative impact on capacities in FLB. For example, compared with monolinguals, bilinguals develop better inhibitory control, theory of mind (Goetz, 2003) and task-switching (Bialystok Martin, 2004).
Raphael Nunez's approach to the evolution of language hypothesises that it involved several pre-adapted 'Modules', but these modules coevolved. That is, an advancement in one module (e.g. more stable voice source, see Demolin, 2010) could cause an advancement in another (e.g. vocal learning), which could feed back into the first module.
Nunez sees the evolution of meaning as involving the development of a grounded system, ungrounding this system from its original domain, then re-grounding it in another. His work focuses on how gestural instantiations of space were re-grounded to convey information about time. For example, one might point behind to indicate an event that occurred in the past. Linguistic expressions of time have also adopted this system.
I suggest that bilingualism can be seen in this way. For instance, being able to learn from several tutors has advantages for increasing signal complexity in some situations. If this ability to learn from individuals could be ungrounded to allow learning from contexts, then this would allow a semantic system to develop. In other words, a kind of bilingualism allows the complex vocal learning mechanisms to be deployed over more general domains.
Okanoya has a similar hypothesis which sees string segmentation and context segmentation as necessary preadaptations for a semantic system. Indeed, the Bengalese Finches studied above may not only be doing string segmentation of tutor's songs, but also a king of crude `tutor segmentation'. That is, they select whole sections from different tutors.
The ungrounding theory suggests that the pressure on the original system needs to be lifted by some other mechanism. This may be a change in the environment, or an internal mechanism. It's likely in the case of the Bengalese Finch that its domestication had a large part to play, alleviating the burden of foraging and predation.
Conclusion
Asking whether non-human species have capacities for bilingualism in the broad sense may affect the way we approach bilingualism. This report has reviewed studies which show that animals have capacities compatible with ideas of bilingualism, but without other features of human language. These capacities stem from very basic evolution of cues and being able to learn from multiple tutors.
Further analysis of evidence for bilingual behaviour in animals is required. These include, for example, switching tasks in primates and other animals and the boundaries between different dialects in whale song. Crucially, this analysis, just like for the rest of FLB, relies on a evidence from a great number of studies. If the relevant studies have not been done, the potential for completing them in this project is extremely restricted.
More fundamentally, this report takes an approach to bilingualism that may not be appropriate. The comparative approach was designed to identify and study necessary components of the language faculty. On the other hand, such an approach may show that, from an evolutionary perspective, there is no easy way to define bilingualism, questioning whether there is a difference between monolingualism and bilingualism or even an easy way to distinguish between languages.
References
Bialystok E, & Martin MM (2004). Attention and inhibition in bilingual children: evidence from the dimensional change card sort task. Developmental science, 7 (3), 325-39 PMID: 15595373
D. Demolin (2010). Prosody and recursion in primate vocalisation Proceed- ings of the JAIST International Seminar on the Emergence and Evolution of Linguistic Communication, Kyoto, Japan.
Doupe AJ, & Kuhl PK (1999). Birdsong and human speech: common themes and mechanisms. Annual review of neuroscience, 22, 567-631 PMID: 10202549
Fitch, W. T. (2005). The evolution of language: A comparative review Biology and Philosophy, 20 (2-3), 193-203 : 10.1007/s10539-005-5597-1
Kaminski J, Call J, & Fischer J (2004). Word learning in a domestic dog: evidence for "fast mapping". Science (New York, N.Y.), 304 (5677), 1682-3 PMID: 15192233
Kuhl, P. & Miller, J. D. (1978). Speech perception by the chinchilla: Identification functions for synthetic VOT stimuli The Journal of the Acoustical Society of America, 63 (3) DOI: 10.1121/1.381770
Magrath, R., Pitcher, B., & Gardner, J. (2009). An avian eavesdropping network: alarm signal reliability and heterospecific response Behavioral Ecology, 20 (4), 745-752 DOI: 10.1093/beheco/arp055
Maynard Smith, J., & Harper, D.G.C. (2003). Animal Signals Oxford University Press, Oxford
Oda, R. and Masataka, N. (1996). Interspecific responses of ring-tailed lemurs to playback of antipredator alarm calls given by Verreaux's sifakas. Ethology, 102, 441-453 : 10.1159/000021651
Okanoya, K. (2004). Song syntax in bengalese finches: proximate and ultimate
analyses Advance in the Study of Behaviour, 34, 297-346
Okanoya, K. (2010). Biological preadaptations for language Proceedings of the JAIST International Seminar on the Emergence and Evolution of Linguistic Communication, Kyoto, Japan.
SCOTT-PHILLIPS, T. (2008). Defining biological communication Journal of Evolutionary Biology, 21 (2), 387-395 DOI: 10.1111/j.1420-9101.2007.01497.x
SEYFARTH, R., & CHENEY, D. (1990). The assessment by vervet monkeys of their own and another species' alarm calls Animal Behaviour, 40 (4), 754-764 DOI: 10.1016/S0003-3472(05)80704-3
Soma, M., Hiraiwa-Hasegawa, M., & Okanoya, K. (2009). Song-learning strategies in the Bengalese finch: do chicks choose tutors based on song complexity? Animal Behaviour, 78 (5), 1107-1113 DOI: 10.1016/j.anbehav.2009.08.002
Miki Takahasi, & Kazuo Okanoya (2010). Song Learning in Wild and Domesticated Strains of White-Rumped Munia, Lonchura striata, Compared by Cross-Fostering Procedures: Domestication Increases Song Variability by Decreasing Strain-Specific Bias Ethology
Zuberbühler, K. (2000). Interspecies semantic communication in two forest primates Proceedings: Biological Sciences, 267 (1444), 713-718 DOI: 10.1098/rspb.2000.1061
FLA and FLB
This research project takes an evolutionary approach to Bilingualism. One of the most difficult problems faced so far is identifying the role of bilingualism in the cultural evolution of language. Is it a product or a catalyst? Firstly, I'm not sure whether this has been considered to any great extent. However, I suggest that the implicit assumption in the vast majority of work in both the areas of Bilingualism and Language Evolution has been that bilingualism is a product of the merging of homogenous language communities. This report explicitly asks the question: Which came first - Language or Bilingualism? That is, did the capacity for bilingualism develop from a pressure to learn multiple existing languages or was it a capacity which existed before human languages were established and influenced their arrival?
The latter hypothesis seems to be non-sensical. How can individuals have the ability to learn more than one language when there are no languages to be learned? Here, I'd like to make a distinction between two kinds of bilingualism, following the approach of Hauser Chomsky Fitch (2002). Bilingualism in the narrow sense means the ability to learn several human languages. This is obviously a human-only trait. Bilingualism in the broad sense refers to the general capacity to acquire more than one signalling system. Depending on how one defines signalling systems, this capacity may be shared with many other animals, both closely and distantly related. Of course, defining what constitutes a single signalling system is difficult, let alone defining language or bilingualism. However, it's hoped that the approach taken in this paper will help towards this goal by considering the features of the phenomenon we wish to define.
Before considering this possibility, the comparative approach to language evolution is presented. Fitch (2005 and others) approaches the study of the evolution of language by considering what elements contribute towards the `Faculty of Language'. In the broad sense of the term, this covers all the prerequisite elements that are required for linguistic communication. This involves cognitive capacities such as acoustic string segmentation and semantic processing, but also much more basic features such as memory. That is, features of the Faculty of Language in the broad sense (FLB) are found in humans and animals. The narrow sense of the term (FLN) refers to those capacities which are involved in language alone. There is much more debate about what these elements are. Recursive processing has been suggested as one example.
The comparative approach has been used to answer the question of what belongs to FLN and to FLB. Animals have been shown to be capable of a number of processes required for language, including categorical perception of speech sounds (Kuhl & Miller, 2978) and Mutual Exclusivity (Juliane & Kaminski, 2004). From studies of divergent and convergent evolution of these traits, some important features have been identified. For example, many species which exhibit vocal learning have direct neural connections between the brain and vocal motors, while non-vocal learners do not (see Doupe, 1999).
This report suggests that this approach should be adopted for the study of Bilingualism. Such an approach would seek to answer whether bilingualism is a uniquely human capacity. If it turns out that other animals also have this capacity, then the role of bilingualism in the evolution of language can be re-assessed.
However, there is a large initial problem. Even FLB only consists of capacities that are required for language. Bilingualism in the broad sense, however, is not required in order to speak a language. This problem may be due to the individual-level bias to the idea of the 'Faculty of Language'. Its primary aim is to describe capacities that an individual organism requires, rather than a community. Therefore, bilingualism may not be part of the FLB, and simply a product of cultural interaction. However, the comparative approach can help verify this hypothesis if social animals exhibit the capacity for bilingualism. That is, if bilingualism comes from cultural interaction alone, there should be no non-social animals which have the capacity for it.
Bilingualism in Bengalese Finches
If other species exhibit bilingualism, then this is evidence that bilingualism developed before human language. Takahasi & Okanoya (2010) study the vocal learning patterns of the Bengalese Finch. These are a domesticated breed descended from wild White Backed Munia. The Bengalese Finch exhibits very complex song patterns in comparison to the White Backed Munia.
Takahasi & Okanoya (2010) carry out a cross-fostering experiment where Munias are brought up by Finches, and Finches are brought up by Munias. The Munias tended to have a stronger preference for copying Munia songs, while the Finches are not so disposed towards their own strain's song. That is, Finches have more flexibility in learning. It is hypothesised that this is because there is a pressure on Munias to identify their own strain in the wild where there are mixed flocks, while this pressure has been masked for Finches by domestication and isolation.
However, is this really `Bilingualism'? The problem is that, although there is flexibility in the sources of acquisition, the birds do not have the same flexibility in production. That is, as I understand it, they still develop only one song (i.e. they can't sing elements of A and B's songs in the morning, then elements of C and D's songs in the evening). Furthermore, the idea of 'comprehension' is more difficult to apply, since there is no semantics.
It has been suggested that Bengalese Finches have developed song complexity as a sexual display (Okanoya, 2004). Following from this, Soma et al. (2009) find that chicks select tutors based on their song complexity. Also, Okanoya (2010) presents some evidence to suggest that Benglaese Finches learn from many tutors. That is, they splice whole segments of songs from many other individuals to create their own song. In this sense, learning from multiple tutors increases the complexity of the song and so increases the attractiveness and fitness of the individual.
The ability to learn syntactic sequences from many tutors has apparently occurred in a system with no semantics. This may suggest that bilingualism at the syntactic level emerged before bilingualism at the lexical level, opposite to the order implicitly assumed by many. One big advantage of cultural evolution is that individuals can inherit information from multiple sources, whereas there are a limited number of biological parents. This is the core of what I mean by Bilingualism being a preadaptation for language: part of the acquisition of human languages requires the flexibility afforded by bilingualism.
Counter Arguments
This phenomenon in Bengalese Finches is interesting, but may not help with our question. Although the complexity of the system has increased due to a change in the environment (domestication), whether this was initially enabled by learning from multiple tutors is not clear.
Also, Okanoya has shown that vocal learners who co-inhabit areas with other species of vocal learners have less complex song. That is, song complexity does not help species identification. Therefore, if the capacity for bilingualism developed in humans before language, it's likely that there was little pressure on vocal cues for species identification.
Inter-species semantic communication
Many species also communicate vocally with other species. Vervet monkeys respond to the territorial and alarm calls of superb starlings (Seyfarth Cheney, 1990). Ring-tailed lemurs respond to the alarm calls of Verreaux's sifakas (Oda Masataka, 1996). However, captive ring-tailed lemurs who had never heard the sifakas' alarm calls also responded appropriately to playbacks. Oda and Masataka argue that they are therefore responding to shared acoustic features rather than to an associated meaning. Although in most examples of inter-species communication do not involve the transference of 'concepts', some examples do show evidence for this.
Zuberbuhler (2000) studied communication between Diana monkeys and Campbell's monkeys. Diana monkeys respond appropriately to Campbell's monkeys' alarm calls for leopards and eagles. Furthermore, their responses suggest they are attending to the meaning rather than the acoustic signal. If a Diana monkey hears a leopard or a leopard alarm call, it calls out loudly, but if it hears a second leopard or leopard alarm, it is quieter, presumably because of the risk of predation (the same is true of eagle alarms). Diana monkeys were primed with Campbell alarms for either leopards or eagles then probed with either eagle or leopard sounds (growls and shrieks). They responded loudly to each combination, apart from where the Campbell alarm corresponded to the predator type (e.g. Campbell leopard alarm followed by a leopard sound). In these cases, the Diana monkeys were quieter, suggesting that they thought the predator was already present.
Zuberbuhler concludes that "Diana monkeys can flexibly use and assess information derived from the communication of other species" and that "semantic understanding can be based on arbitrary signals, as it is the
case for word meaning" (Zuberbuhler, 2000, p. 717). Diana monkeys seem to understand the same concept from two different calls. I argue that this is bilingualism in the broad sense at the lexical-like level.
Again, Diana Monkeys are limited by their physiology in terms of production of the Campbell's alarms. However, the information transfer from Campbell's monkeys to Diana monkeys is not 'communication' as defined by MaynardSmith Harper, 2003) (also see Scott-Phillips, 2008). That is, although the Campbell's calls affect the behaviour of the Diana monkeys, they did not evolve to do this (they are cues, not signals). Therefore, I'd like to suggest that the origins of the capacity for bilingualism originates in the evolution from cues to signals.
However, these responses may not be learned. Furthermore, there is no current evidence to suggest that Campbell's reciprocate in their comprehension of Diana Monkey's calls. The latter issue is discussed by Magrath (2009) who study the alarm call responses of 3 ecologically distinct avian species and find that responses may be reciprocal, but not necessarily symmetrical. Different species reacted to each other's alarm calls in proportion to the 'reliability' of the call as a cue to one of the listener's predators. That is, not all predators of species A are predators of species B, so the A's alarms are not always reliable for species B, and species B responds appropriately. In Magrath (2009)'s study, some species responded in the same way to three different calls. Again, this is evidence for bilingualism in the broad sense.
This raises an interesting question of 'reliability' or 'relevance' (as in Relevance theory, Sperber Wilson, 1995) in animal communications. Much of animal communication is limited to and grounded in information relevant to shared survival interests, that is, food, predators and mating. Humans are capable of communicating about topics beyond their immediate survival needs. This difference possibly requires the of 'ungrounding' of signals from the domains in which they evolved (see the next section).
Bilingualism's impact on FLB
Although bilingualism may not be necessary for the acquisition of language, and so could arguably not be part of FLN, learning two languages does seem to have a qualitative impact on capacities in FLB. For example, compared with monolinguals, bilinguals develop better inhibitory control, theory of mind (Goetz, 2003) and task-switching (Bialystok Martin, 2004).
Raphael Nunez's approach to the evolution of language hypothesises that it involved several pre-adapted 'Modules', but these modules coevolved. That is, an advancement in one module (e.g. more stable voice source, see Demolin, 2010) could cause an advancement in another (e.g. vocal learning), which could feed back into the first module.
Nunez sees the evolution of meaning as involving the development of a grounded system, ungrounding this system from its original domain, then re-grounding it in another. His work focuses on how gestural instantiations of space were re-grounded to convey information about time. For example, one might point behind to indicate an event that occurred in the past. Linguistic expressions of time have also adopted this system.
I suggest that bilingualism can be seen in this way. For instance, being able to learn from several tutors has advantages for increasing signal complexity in some situations. If this ability to learn from individuals could be ungrounded to allow learning from contexts, then this would allow a semantic system to develop. In other words, a kind of bilingualism allows the complex vocal learning mechanisms to be deployed over more general domains.
Okanoya has a similar hypothesis which sees string segmentation and context segmentation as necessary preadaptations for a semantic system. Indeed, the Bengalese Finches studied above may not only be doing string segmentation of tutor's songs, but also a king of crude `tutor segmentation'. That is, they select whole sections from different tutors.
The ungrounding theory suggests that the pressure on the original system needs to be lifted by some other mechanism. This may be a change in the environment, or an internal mechanism. It's likely in the case of the Bengalese Finch that its domestication had a large part to play, alleviating the burden of foraging and predation.
Conclusion
Asking whether non-human species have capacities for bilingualism in the broad sense may affect the way we approach bilingualism. This report has reviewed studies which show that animals have capacities compatible with ideas of bilingualism, but without other features of human language. These capacities stem from very basic evolution of cues and being able to learn from multiple tutors.
Further analysis of evidence for bilingual behaviour in animals is required. These include, for example, switching tasks in primates and other animals and the boundaries between different dialects in whale song. Crucially, this analysis, just like for the rest of FLB, relies on a evidence from a great number of studies. If the relevant studies have not been done, the potential for completing them in this project is extremely restricted.
More fundamentally, this report takes an approach to bilingualism that may not be appropriate. The comparative approach was designed to identify and study necessary components of the language faculty. On the other hand, such an approach may show that, from an evolutionary perspective, there is no easy way to define bilingualism, questioning whether there is a difference between monolingualism and bilingualism or even an easy way to distinguish between languages.
References
Bialystok E, & Martin MM (2004). Attention and inhibition in bilingual children: evidence from the dimensional change card sort task. Developmental science, 7 (3), 325-39 PMID: 15595373
D. Demolin (2010). Prosody and recursion in primate vocalisation Proceed- ings of the JAIST International Seminar on the Emergence and Evolution of Linguistic Communication, Kyoto, Japan.
Doupe AJ, & Kuhl PK (1999). Birdsong and human speech: common themes and mechanisms. Annual review of neuroscience, 22, 567-631 PMID: 10202549
Fitch, W. T. (2005). The evolution of language: A comparative review Biology and Philosophy, 20 (2-3), 193-203 : 10.1007/s10539-005-5597-1
Kaminski J, Call J, & Fischer J (2004). Word learning in a domestic dog: evidence for "fast mapping". Science (New York, N.Y.), 304 (5677), 1682-3 PMID: 15192233
Kuhl, P. & Miller, J. D. (1978). Speech perception by the chinchilla: Identification functions for synthetic VOT stimuli The Journal of the Acoustical Society of America, 63 (3) DOI: 10.1121/1.381770
Magrath, R., Pitcher, B., & Gardner, J. (2009). An avian eavesdropping network: alarm signal reliability and heterospecific response Behavioral Ecology, 20 (4), 745-752 DOI: 10.1093/beheco/arp055
Maynard Smith, J., & Harper, D.G.C. (2003). Animal Signals Oxford University Press, Oxford
Oda, R. and Masataka, N. (1996). Interspecific responses of ring-tailed lemurs to playback of antipredator alarm calls given by Verreaux's sifakas. Ethology, 102, 441-453 : 10.1159/000021651
Okanoya, K. (2004). Song syntax in bengalese finches: proximate and ultimate
analyses Advance in the Study of Behaviour, 34, 297-346
Okanoya, K. (2010). Biological preadaptations for language Proceedings of the JAIST International Seminar on the Emergence and Evolution of Linguistic Communication, Kyoto, Japan.
SCOTT-PHILLIPS, T. (2008). Defining biological communication Journal of Evolutionary Biology, 21 (2), 387-395 DOI: 10.1111/j.1420-9101.2007.01497.x
SEYFARTH, R., & CHENEY, D. (1990). The assessment by vervet monkeys of their own and another species' alarm calls Animal Behaviour, 40 (4), 754-764 DOI: 10.1016/S0003-3472(05)80704-3
Soma, M., Hiraiwa-Hasegawa, M., & Okanoya, K. (2009). Song-learning strategies in the Bengalese finch: do chicks choose tutors based on song complexity? Animal Behaviour, 78 (5), 1107-1113 DOI: 10.1016/j.anbehav.2009.08.002
Miki Takahasi, & Kazuo Okanoya (2010). Song Learning in Wild and Domesticated Strains of White-Rumped Munia, Lonchura striata, Compared by Cross-Fostering Procedures: Domestication Increases Song Variability by Decreasing Strain-Specific Bias Ethology
Zuberbühler, K. (2000). Interspecies semantic communication in two forest primates Proceedings: Biological Sciences, 267 (1444), 713-718 DOI: 10.1098/rspb.2000.1061
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