4.0 The Self-domestication of humans
Why did bird “language” (or, birdsongs) not evolve to the extent that human language (natural language) did? We may approach this question by examining the converse: Why did human language evolve to an extent unobserved in the communication system of birds? One hypothesis is the human self-domestication hypothesis. The basic idea of self-domestication is that among the driving forces of human evolution, humans selected their companions depending on prosociality. They preferred mates who were more intelligent, creative, and articulate; prosocial and cooperative behaviours were desirable in a mate. This selective pressure for more cooperation caused humans to evolve differently from other hominids, both behaviorally and cognitively. It is postulated that Self-domestication may have facilitated the emergence of complex behaviours via cultural evolution, in particular, of more complex languages in order to support more complex cultural practices (Thomas, 1994).
We may also think of self-domestication as follows: early humans adapted the environment for themselves (e.g. by making tools and erecting shelters), and subsequent generations gradually adapted to the increasingly man-made environment. Self-domestication (of humans) in this sense occurred through generations of changing and adapting to the environment without direct interference by other non-human species. As aforementioned, the selection of mates who had more prosocial behaviour was one of the driving forces of human evolution. This direction of human evolution–towards a species that possesses an increasingly complex language–potentially played a role in shaping the kind of physical environment that humans made for themselves. Therefore, it is important to consider the different factors that were at play in the self-domestication of humans, and view the process holistically.
4.1 Birds in the wild vs. Birds in captivity
Unlike humans, birds did not undergo the process of self-domestication, and this is one plausible reason bird songs did not evolve to possess all the criteria of a language. This hypothesis is supported by the observation that domesticated songbirds have songs that are more complex than their wild counterparts (Erard and Matacic, 2018; Thomas and Kirby, 2018). One example is the Bengalese finch (Lonchura striata domestica), a domesticated, possibly hybrid, descendent of the white-rumped munia (Lonchura striata). According to avicultural literature, white-rumped munias were imported into Japan in 1762 and domesticated due to their tameness. The domesticated variety of white-rumped munias were then referred to as Bengalese finches. This variety does not occur in the wild. The songs of white-rumped munias are observed to be less complex and melodious, as well as more repetitive than the songs of their domesticated descendents. There are two main reasons for the disparity in song complexity between the wild and domestic songbirds including the presence of (1) predators and (2) sympatric (i.e. closely-related or overlapping) species in the wild, including the spotted munia (Lonchura punctulata), a sympatric species of the white-rumped munia (Okanoya, 2015).
Firstly, for the white-rumped munia, singing in the wild is a dangerous activity that draws the attention of not only his potential mate, but also its predators. Consequently, the male munia bird spends less time singing as compared to his Bengalese finch counterpart. There is reduced cultural transmission in the wild munia, whereby the father spends less time teaching his song, and the son spends less time practising the inherited songs. Reduced singing time also means having less time to improvise and introduce variations to the song. Moreover, the learner’s songs are observed to have a higher fidelity to his tutor’s song. Secondly, the presence of sympatric species means that the white-rumped munias have to keep their songs simple to help distinguish their songs from the songs of other closely related bird species, such as the spotted munias. This reduces the likelihood of hybridisation and its associated disadvantages, such as lower fertility in the offspring (Okanoya, 2015; Thomas, 1994).
On the other hand, the domesticated Bengalese finch does not face the risk of being heard by predators in the safety of his enclosure, and is thus free to sing to his heart’s content. This leads to an increased role for cultural transmission of songs from father to son. With an increased singing time, the learner is able to further experiment with the tunes, improvise, and add variations to the songs. The absence of sympatric speciation means that their songs can be as colourful as they want it to be. The result is a lower fidelity of the learner’s song to his tutor’s song. Without constraints on their song systems, Bengalese finches were free to develop their songs to a higher level of complexity. This might have been one of the factors that led to the evolution of a larger brain interfacialis (one of the song control circuits) in the Bengalese finch to help it cope with the complexities of its song, which in turn further allowed for development of even more complex songs (Thomas, 1994). One Science article discusses the comparison between the songs of the two songbird species presented by ornithologist Kazuo Okanoya.
Munia song (K. Okanoya)
While domestication is evidenced to contribute to the evolution of language, or bird songs in this case, the lack of self-domestication in songbirds is a plausible reason that bird songs did not evolve to the extent that human language did.
4.2 Cooperation, tool-making, and human language evolution
As mentioned above, cooperation led to greater cognitive abilities in humans. Combined with extensive physical abilities, humans developed in the area of tool-making (Stout, 2012). This activity is believed to have facilitated the evolution of human language in more than one way. One instance might be the evolution of words as types of signals. For example, consider the word ‘snake’. For the early or pre-humans, the exclamation “snake!” was likely predominantly a danger signal. When humans later developed tools for hunting, the call ‘snake’ evolved to signal not only danger, but also the presence of a prey in one’s surroundings (i.e. food). Today, the modern man does not necessarily link the word ‘snake’ to a danger signal or food; we have become creative with the use of the word. For example, man conceived of Medusa with venomous snakes for hair, to represent a certain image of the Greek mythological monster.
In contrast, we can imagine that for birds, alarm calls that signal danger would not evolve to signal something else; the bird’s call for ‘snake’ will always only signal danger. One plausible explanation is that such calls do not evolve so as to retain its survival value. Therefore, we may think of bird calls as primarily for survival purposes (i.e. for preservation of both self and species), and perhaps secondarily for pleasure–a luxury not all birds can afford.
Then again, readers may ask: Do songbirds sing for their own pleasure? Perhaps they do, from time to time. For domesticated songbirds especially, it may start off with experimenting with different sounds, just because their environment allows for it at little to no cost (see section 4.1). Over time, these birds may improvise and develop their “own” songs. Seeing as how this is a self-motivated process not done out of necessity, it might suggest that some learners do find pleasure in singing, which in turn allows for the development of more elaborate songs under suitable environmental conditions. One possible test for this might be to monitor the neural activity of songbirds in the wild and in captivity. Specifically, a test could be designed to monitor and measure the dopamine signalling in white-rumped munias and Bengalese finches during their practice singing sessions. This test will possibly determine if there is a general discrepancy in the amount of dopamine signalling between the two groups. One difficulty of this study, however, is the necessary domestication of wild munias to some extent, which might interfere with the results of the study.
In short, we humans owe the evolution of our language to our greater physical and intellectual capabilities, which allowed for the development of human language to a degree not attained by birds.
4.3 Abstraction and Language evolution
Another theory regarding the more sophisticated development of human language versus bird songs discusses the link between evolutionary changes in the human brain and the emergence of abstract thought. It is proposed that the beginning of abstract thought and creative pursuits such as cave art, coincides with evolutionary changes in the human brain between 70,000 and 100,000 years ago (Saini, 2015). This could have potentially sparked the birth of the complex, sophisticated form of language we use today. Some linguists propose that similarities in speech-associated brain structures and genes in humans and birds contribute to the parallels in the evolution of human language and birdsongs. Others, including birdsong expert Johan Bolhuis, are however skeptical about this explanation of the origins of human language. In his book Aspects of the Theory of Syntax (1964), American intellectual Noam Chomsky proposes the theory of “universal grammar”, which posits the innateness of grammar to humans. The acquisition of grammar requires the capability to form abstract thoughts, such that illogical or nonsensical sentences can still be grammatically sound. Human language might be the only language that features grammar, and we owe this to our ability for abstract thinking.
Listed below are some distinguishing factors between birds and humans that may be worth consideration:
- Unlike (some) humans, birds probably do not try to develop an understanding of the world using a language other than their own; we may assume parallels between such an activity and the arbitrariness of human language. Just as how humans give meaning to arbitrary sounds, we may try to study and give meaning to another animal’s call, sometimes using clues from our environment (e.g. a skinny stray cat’s meow could mean hunger), other times attaching meaning to the sound possibly based on one’s whims (e.g. I think my cat misses me when he meows like this).
- Humans try to find meaning in words. For example, consider the word ‘snake’ which used to signal danger. Now, we may use it to describe a snaking road. Birds would never do this. (At least, they are not observed to do so). Therefore, as observed, birds likely do not have the capacity for abstraction and concepts.
4.4 Miscellaneous thoughts
- Are abstract thoughts communicated only with words, or can they be present in other forms of animal communication such as birdsongs, gestures, sign language, etc.?
- Do birds have abstract thought/understand concepts?
- The understanding of concepts/abstract idea was observed in Alex, who could count. Did Alex go through a process of translation from his language to human language when he exhibited the ability to count (capacity for abstraction)? It would be interesting to study if they exhibited such behaviour in their own “language”.