Music s Place in Evolutionary Psychology

Transcription

1 Music s Place in Evolutionary Psychology Abstract Whether producing or listening to it, music has historically had and continues to have an impact on the lives of a wide range of people. However, the exact role of music in our evolutionary history is unclear; debate exists as to whether music is a psychological adaptation specifically evolved to help humans increase survival in their ancestral environments. In this paper, I present and holistically analyze the psychological, biological, sociological, and anthropological arguments of various proponents of each side of this debate. Through analytical discussion, I synthesize the main arguments for music as an evolutionary adaptation and show that current evidence remains insufficient to deem music an adaptation. Using the criticisms against music as an adaptation, I propose the types of evidence that would be necessary to show that human brains are adapted to make music, specifically biological remnants of a psychological adaptation. Finally, I attempt to further nuance and then resolve the two opposing arguments of this debate. I also posit a new role that music may play in the life history of humans, and I suggest future directions of research into uncovering the relevance of music to human evolutionary psychology. Keywords: Music; Adaptation; Evolutionary psychology; Music cognition; Neurobiology of music

2 Introduction The ability of music to impact positively the human psyche is apparent from the ubiquity of varying forms of music in culturally different societies around the world. But is music an evolutionary adaptation of the human mind, specifically brought to fruition by a selective advantage with which it endowed humans, or is it merely an invention that humans have developed only for pleasure? In order to evaluate music in the light of evolutionary biology, we must first define what it is that would constitute an adaptation of the human mind. The biologist Walter J. Bock (1980, p. 221) posits a relatively broad definition of adaptation as a feature having properties of form and function which permit the organism to maintain successfully the [synergy] between a biological role of that feature and a stated selection force. Because psychology is a science of the mind, for the purposes of this paper I will confine this definition to biological roles of and selection on the human brain. With an analysis of the evolutionary significance of both sides of the debate on music, I will comment on the degree to which music appears to be an adaptation. The Argument for Music as Adaptation With this independently generated definition in mind, we now turn to the arguments put forth that music is an adaptation. To represent the class of scientists advancing this argument (a group to which I will hereinafter refer as the

3 adaptationists ), Penelope Lewis s argument approaches and summarizes well the position from its roots in both anthropological and biological evidence. Lewis (2002) points to the widespread existence of music within different cultures, claiming that music s constancy across non-constant cultural environments shows that it is not merely a cultural or societal construction, and this further implies its deep-seated nature within human biology. Lewis (2002) also cites the existence of musical instruments, like bone flutes, as evidence of the ancient nature of music and its involvement with prehistoric humans. Building on this, the musicologist David Huron (2001) argues that simpler forms of music, such as singing, could have predated more complex instruments by 200,000 years. Further adding to the argument for an ancient musical adaptation by studying musical predisposition in infants, the psychologist Sandra Trehub (2001) notes the ability of infants to recognize musical patterns, specifically their ability to recognize a tone sequence as the relative values when it has been transposed in pitch or altered wholesale in tempo. Approaching the debate from an evolutionary ethological standpoint, Huron further cites the anthropologist David Werner s (1984) on the study on the Mekranoti Indians, a hunter-gatherer people living in the Amazon who devote more than two hours each day to singing, suggesting that the predominance of music within the culture of these peoples, whom anthropologists posit live in a manner similar to that of pre-modern humans, indicates music s ancient role in our development as a species. Calling on the ancient nature of music and its uniformity across cultures, the adaptationists have laid the groundwork for a theory of music s evolutionary history in

4 humans. Lewis s (2002) proposition on the universality of music across cultures seems on the surface to show that music had some evolutionary value to ancestral humans. However, a closer inspection of the ways in which humans make and respond to music specifically, a lack of developmental biological stages with regards to musical skill show that this assertion is false; we will return to this topic in the discussion on comparisons between language and music. In addition, Trehub s (2001) study shows that infants respond to musical stimuli without prior training, but this does not prove that humans have an innate ability for music. Rather, it could be some other adaptive abilities of audition and sound analysis like responding to mother s voice that, as a by-product, allows infants to also discriminate musical tone sequences; we will also return to this topic to nuance the non-adaptationist viewpoint. Despite this, the finding of musical instruments in prehistoric human cultures does indeed show that music has, in some groups of humans, existed since antiquity, and this implies that music could possibly have had an impact on the evolution of the brain. However, though the predominance of music in hunter-gatherer cultures does corroborate music as a feature that could have arisen in prehistoric times, it does not show that music is necessarily an adaptation; many ancient artifices, such as our appendixes, have no adaptive value for humans, so music cannot be an adaptation simply by virtue of its being old. Furthermore, music could simply be an invention generated by man, not something to which our brains are specifically designed to respond; by Bock s (1980) definition, adaptationists would need to show the biological form or basis of music, in addition to a selective pressure that could cause the biological basis of music to increase in

5 frequency in the population, and verify that the two are consummate in form matching function. To enable humans to respond to a particular selective pressure in the environment, music must have conferred fitness benefits on ancestral humans. Huron (2001) posits that music is beneficial because it contributes to social group bonding, and suggests as the mechanism increased oxytocin release during music listening (Freeman, 1995), which increases trust and thus bonding between individuals. Another hypothesis, proffered by the psychologist Geoffrey Miller (2000), posits that the force of sexual selection could act as this selective pressure, in which case the evolutionary benefit of music lies in its role as an indicator of fitness as a proxy measurement of a male s health, strength, status, and ability to invest expendable energy in rearing offspring that would increase a male human s attractiveness to a female and thus would also increase his chances of reproductive success. To evidence his claim, Miller (2000) mined the data of over six thousand records of various genres produced by various companies and found that males perform and generate ten times more musical pieces than females. Furthermore, in Miller s (2000) data, males musical output peaks on average in young adulthood near age thirty, a time point in a male s life that also corresponds with average peak in mate seeking and mating activity. The adaptationists hypotheses about the benefits and selection dynamics of music are certainly possible mechanisms by which music could have influenced human evolution as an adaptation, but the adaptationists provide no concrete evidence to show that music has definitively, in the environment of evolutionary adaptation, performed

6 the aforementioned roles in human interactions. Miller s theory of a sexual selection force promoting music as an adaptation holds in an abstract evolutionary biological sense, but fails to provide proof that music necessarily indicates higher fitness reproductive or otherwise or that sexual selection is the actual mechanism by which music performance becomes a widespread phenomenon in humans. Further, Miller s and Huron s claims and cited pieces of evidence are both subject to confounding factors. In Miller s sample of records, some unseen social capital possibly in the form of social norms could cause both an average reproductive age of around thirty (as measured by childbirths, which does not indicate that men are not sexually active at a younger age) and a greater emphasis on music education for boys than for girls, leading to a higher number of male professional musicians. In Huron s claims, music could be a surface-level stimulus activating an adaptive function in humans for example, a positive response to an ability to parse out the different parts of an auditory scene, which could be adaptive because of its benefits during hunting and avoiding other predators which is the real cause of increased positive hormone release. Thus, the adaptationists fail to meet Bock s (1980) standard for an adaptation in that they hypothesize a possible evolutionary pressure and corresponding functional benefits from music in Miller s sexual selection argument but do not verify that humans have biological form matching this pressure that is, secondary characteristics that would arise as a consequence of a selection for music. To identify potential physiological characteristics that would evidence an adaptive role of music in shaping human biology, the adaptationists look to

7 neurobiology. Lewis (2002) cites the human brain s response to music as shown by several neurological studies as evidence for music s adaptive impact. Measuring electrical activity in the brains of non-musicians, Trainor et al. (2002) show that the auditory cortex responds to and encodes information about the pitch contour of a series of musical notes, even while subjects are distracted by other tasks. Lewis (2002) suggests from the Trainor et al. data that the pre-attentive processing of certain elements of music in the brain raises the possibility of brain structures specifically for music. Further, Blood et al. (1999) showed that emotional responses to different kinds of music are correlated with heightened brain activity in the paralimbic system, an evolutionarily old part of the brain; Lewis (2002) and other adaptationists argue that this data supports an evolutionarily old human reaction to music. Again, the adaptationists further lay the foundational evidence for music as an adaptation by showing that music can, as a single stimulus, elicit physiological brain responses from humans. However, the current neurobiological research cited by adaptationists is not sufficient to show that music is an evolutionary adaptation in and of itself because the brain regions and structures activated are not specific to music; other activities, like the prosody of speech, could pre-attentively activate the auditory cortex (Doeller et al., 2003). The paralimbic system, which is involved in some emotion processing, could also clearly be activated by other stimuli. Further experiments would need to be conducted to show this specific function of the human body and not just the human mind that is dedicated entirely to music.

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9 The Argument for Music as Non-adaptive Given that the adaptationists have not provided sufficient evidence to conclusively show that music is an adaptation, I will now examine the argument for music as non-adaptive with the intent of shedding light on further evolutionary biology arguments which nuance the argument against adaptation. Specifically, after evaluating the non-adaptationists claims, I will look to these same claims in combination with other evidence to posit that music is in fact not an adaptation in an evolutionary or ultimate sense, but is rather a human invention that, in a proximate sense, can change the human brain in significant ways. To represent the class of scientists advancing this argument (a group to which I will hereinafter refer as the non-adaptationists ), Steven Pinker s argument well encapsulates the reasoning and analysis of this side of the debate. The non-adaptationist viewpoint is famously summarized by Pinker s assertion that music is auditory cheesecake (2003, p. 534), a reduction of music to a sweet but entirely evolutionarily useless treat that we enjoy not because of any benefit inherent in it, but rather by virtue of our other faculties and adaptive proclivities. Pinker (2003) argues that music shows no independently verified signs of engineering design toward evolutionary advantage, and he (Pinker, 1997) posits that music has no evolutionary benefit for humans, as music consumes time and energy. Pinker (1997) goes on to say that arguments for music s survival and reproductive benefits for example, music enhances social bonds do not explain why music has this effect. This reasoning is supported also by other non-adaptationists, including John Barrow (1995) and Dan Sperber (1996).

10 The non-adaptationists framework of reasoning is valid in principle: if no traces of humans physiological or psychological development point to an evolutionary design specifically for musical capabilities independent of other human faculties (e.g., language or audition in general), then there exists a lack of a definite biological role and definite function, and thus we cannot conclusively classify music itself as an adaptation simply by definition. However, Pinker (1997) goes too far in his implication that music causes a diversion of time and energy and thus cannot have reproductive benefit for humans; a basic tenet of evolutionary biology states that if the benefits of an adaptation outweigh its costs, then natural selection will still drive the adaptation to higher frequency in the population. For example, the human brain comes at the costs of long gestation periods, large heads, and a disproportionately large energy consumption for its size, yet all humans have large brains and fossil records indicate that brain size has been increasing over the course of human evolution. Thus, Pinker s assertion is not a valid criticism because it precludes the possibility of any reproductive fitness gained from music above and beyond the energy expended on it in fact, evidence suggests that music positively affects speech perception in young adults and may also lead to increased perceptive fitness as a person ages (Parbery-Clark et al., 2011), which could conceivably lead to increased reproductive success; this is a topic to which we will return in a resolution of the adaptationist and non-adaptationist positions. The non-adaptationists dismissal of observational and associational studies, such as data on music s power to alleviate negative emotions (Thayer, 1996), is a sensible criticism from a psychological science standpoint. Such observations fail to

11 show necessity with respect to the amelioration of negative emotions, as music did not necessarily alleviate negative emotions in all subjects. In addition, such studies fail to show sufficiency to elicit the same emotional response from all people; where a stimulus like the presence of a snake would nearly universally elicit fear, music as a stimulus does not elicit a uniform response across ages and cultures, thus providing evidence that humans are not biologically prepared in the sense of the term John Garcia coined or pre-conditioned to have a physiological or psychological response to music. It is precisely this lack of homogeneity and universality in musical expression across humans to which non-adaptationists point as evidence for their reasoning. This evidence often involves comparing music to language, as features of language have been shown by simulation to increase in frequency under evolutionary conditions (Hurford, 1989). Pinker (1997) points out that musical tastes and levels of sophistication have varied across time, cultures, and individuals, while all neurologically normal children spontaneously generate and deduce complex abstract language concepts, regardless of the local language. In addition, musical abilities vary greatly across otherwise psychologically normal individuals (Pinker, 1997), and those who play an instrument need sustained and direct training to develop musical skills, while all children advance through standard stages of language acquisition (Pinker 1995). Building on this comparison to language, non-adaptationists offer an alternative theory of the mind s response to music in terms of its ability to activate other faculties of the brain. Barrow (1995) posits that, given the evidence showing non-parallelism

12 between language and music in acquisition, music arose because sensitivity for specific sound patterns may have been advantageous. Elaborating on this other brain sensitivity, Pinker (1997) states that while we are not explicitly evolved to have a capacity for music, we are adapted to respond to language, emotional calls, and motor control patterns; music, to Pinker, is an epiphenomenon of these adaptive mental faculties. Specifically, current evidence suggests that music co-opts our faculty for auditory scene analysis with respect to note frequencies, rhythm and timing, and timber of the sound; ironically, it is the adaptationist Sandra Trehub whose evidence most readily supports this conclusion. Trehub s (2001) data on infant responsiveness to music do not necessarily support her conclusion of a biologically-based human predisposition specifically to music. Rather, they suggest that humans have a predisposition for some other auditory capabilities in a broader sense, particularly including mother s song since this is the natural context in which babies would hear music. In fact, Trehub s (2001) data do show that the infants prefer maternal song over other styles of singing. This general auditory capability would be adaptive, as babies that can recognize their mothers by voice and respond appropriately would have a better survival advantage. Given the critiques leveled by non-adaptationists, what would sufficient evidence for music as adaptation look like? Comparison of music to language, a human faculty that shows independently verified signs of being an adaptation (Pinker, 2003; Hurford, 1989), reveals a higher degree to which music must demonstrate integration into human brain function. The non-adaptationists contention that abstract language

13 concepts and the acquisition process of language are both fairly homogeneous across cultures and individuals suggests that language is a species-wide adaptation (as convergent evolution for language between populations would likely have yielded different timing of developmental stages in childhood acquisition given randomness of mutation). In contrast, there have been no studies showing universal stages of musical skill acquisition in children; some people do not even participate at all in making music. While evidence suggests that music is non-adaptive but that humans have innate sound processing abilities, it is also important to note that music is not reducible to cheesecake as Pinker (2003) suggests. The notion of cheesecake is one of eliciting firing patterns in the brain as an epiphenomenon of our evolutionarily-rooted desires for energy-rich foods; cheesecake has no adaptive value because it cannot give humans any benefit outside of a proximate context. In contrast, Halwani et al. (2011) showed that music has the ability to change the actual structure of the brain, in terms of tract volume and functional anisotropy of certain regions including the arcuate fasciculus. In addition, Parbery-Clark et al. (2011) showed that music positively affects speech perception in aging individuals by slowing down the decline of speech perception ability. These pieces of evidence suggest that music can leave beneficial lifelong physiological changes on the brains of single individuals. Thus, the non-adaptationist claim against music as an adaptation is supported on an evolutionary time scale, but music does show signs of enhancing fitness proximally within an individual practicing it.

14 Resolution, Alternate Positions, and Future Directions for Research If music is not merely cheesecake as Pinker (2003) suggests, then what might it be? The evidence presented here paints a picture of music as a tool, similar in benefit to a hammer or any other piece of technology invented by man that enhances productivity in the general sense. Humans created hammers to build more complex structures for their security and well-being, which does indeed enhance fitness, survival, and reproductive capability, yet humans were not adapted to build hammers specifically; rather, we developed them as a result of our cognitive abilities. Similarly, evidence from studies of music s positive effects on emotion (Thayer, 1996) and speech perception persistence through aging (Parbery-Clark et al., 2011), combined with the understanding that music was not an adaptation in humans environment of evolutionary adaptedness, suggest that humans created music to enhance subjective quality of life measures, which in turn do enhance fitness, survival, and reproductive capability. The key to resolving the adaptation versus non-adaptation debate lies in disentangling proximate and ultimate explanations for music as a human phenomenon. The evidence adduced by adaptationists can be better understood at an individual, proximate level. Neurobiological evidence from Halwani et al. (2011) shows that the brain is not pre-wired in any specific way to respond to music, but rather the physiological brain changes vary depending on the individual and the type of musical experience. A lack of specified neuronal pre-wiring for music as it is seen in other mental faculties, such as language suggests that music affects a human in the span of his own lifetime; in other words, music gives proximal benefit.

15 Current evidence suggests that the human brain responds to music in biologically rooted ways but fails to identify a specific physiological factor, role, or function of music that would conclusively show that music is an evolutionary adaptation by Bock s (1980) definition. This lack of mechanistic biological evidence in the form of actual neural circuitry or physiological characteristics dedicated to music is actually quite promising, as knowledge of the actual mental faculties underlying music appreciation promise to reveal much about the original purposes of developing music. For example, Stephen Brown (2000) proposes several different models of human use of language and music, one of which hypothesizes music as an offshoot development of our faculties for language. Currently, evidence from infants (Trehub, 2001) only supports auditory scene analysis as the mental faculty which music co-opts to bring its proximal benefit; future functional magnetic resonance imaging (fmri) studies can be conducted to examine which other mental faculties e.g., motor command centers for rhythmic motion are active when music is played and experienced. One future direction will be categorizing more completely the adaptive faculties of the mind that respond to language and music; given the current neurobiological research, it does not seem impossible that we will begin to more clearly tease apart the neural circuitry associated with music and with language, and as resolution of imaging studies and brain connectome studies increases, we may find a neural circuit that is specific for musical development that is universal across humans. Given that music is a tool that can only affect individuals over the course of their own lifetimes, further evidence will be required to conclusively characterize the human

16 evolutionary relationship with music. Indeed, Darwin s theory of evolution by natural selection demands that its adaptations arise through traits that can be passed from one generation to the next. One possible way that this could happen with music is through epigenetic modifications: if music were to have some effect on children that upregulated the expression of neural circuitry dedicated to music during their critical periods, music could in theory begin to shape our ever-changing brains. Ultimately, the goal of studying music in the context of evolutionary psychology will be to identify the vestiges of whatever impact music has had on our minds and bodies.

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