The World in Six Songs: How the Musical Brain Created Human Nature (31 page)
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Authors: Daniel J. Levitin
BOOK: The World in Six Songs: How the Musical Brain Created Human Nature
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The enlarged role of education of the human child stands in stark contrast to any other species. And across history, song has been one of the primary ways in which life lessons are taught. Our ancestors discovered that well-formed songs, combining musical and rhythmic redundancies with lyric messages, facilitate both the encoding and transmission of important information—knowledge songs. But it was love songs and the feelings of love that created the social structure in which we bring up children. Men and women form pair-bonds to the lilts of love songs and mutually ensure the care and nurturing of children.
Humanlike pair-bonding and monogamy are rare in the animal kingdom. In the vast majority of the 4,300 species of mammals in the world, adult males and females tend to be solitary, coming together only to copulate; males don’t pair-bond with the mothers of their offspring and they don’t provide paternal care. Even in the most social mammals, such as apes, lions, wolves, and dogs, there is no evidence that males even recognize their own offspring.
In humans, although polygyny (long-term simultaneous sexual relationships between one man and two or more women) has existed as a rare behavior for thousands of years, the dominant mode of relationships is of monogamy, or at least serial monogamy. This requires that we establish bonds and feelings of intense attachment;
love
and its neurochemical correlates can be seen as the evolutionary adaptation that makes these long-term bonds possible. Once the adult male-female love mechanism is in place, it can be easily adapted for parent-child love. In fact, Ian Cross quips, love serves an important function there—human infants can be noisy, fussy, and a lot of trouble, and love for them may be the only thing that prevents many parents from killing their children.
love
and its neurochemical correlates can be seen as the evolutionary adaptation that makes these long-term bonds possible. Once the adult male-female love mechanism is in place, it can be easily adapted for parent-child love. In fact, Ian Cross quips, love serves an important function there—human infants can be noisy, fussy, and a lot of trouble, and love for them may be the only thing that prevents many parents from killing their children.
Love and altruism take on a different quality in humans than in animals (as do many other of our behaviors) because of our awareness of them, our self-consciousness. We can plan how we want to demonstrate our love, we can promise to love. Our perspective-taking ability helps us to recognize that we have to win over the skepticism of our potential mate.
Some readers may object that when considering the survival of the species, and evolutionary adaptations, love does not appear all that important compared to some of the other attributes we’ve seen in
The World in Six Songs.
For example, the drive toward knowledge seems clearly essential—those individuals who enjoyed learning were better able to adapt to changing environmental and social conditions. (And as a consequence, they were favored by natural selection.) Knowledge songs developed as an efficient way to encode, preserve, and transmit information. As early or protohumans left the shelter of the trees for the open savannah, exposing themselves to predators, the drive toward friendship allowed for us to navigate complex social and interpersonal exchanges. Comfort songs helped to reassure infants and others with whom we weren’t in physical contact that we were nearby, and they helped to pick us out of periods of sadness by reminding us that others too had felt sad and recovered.
The World in Six Songs.
For example, the drive toward knowledge seems clearly essential—those individuals who enjoyed learning were better able to adapt to changing environmental and social conditions. (And as a consequence, they were favored by natural selection.) Knowledge songs developed as an efficient way to encode, preserve, and transmit information. As early or protohumans left the shelter of the trees for the open savannah, exposing themselves to predators, the drive toward friendship allowed for us to navigate complex social and interpersonal exchanges. Comfort songs helped to reassure infants and others with whom we weren’t in physical contact that we were nearby, and they helped to pick us out of periods of sadness by reminding us that others too had felt sad and recovered.
Joy songs began as expressions of our own emotional states, signaling to those around us either a positive outlook or the possession of food and shelter resources. Neurochemical boosts associated with joyful singing helped to reinforce joy as a signal for mate selection. Religion and its songs served to bind animal rituals into systems of belief, and ultimately helped to systematize and socialize feelings of hope and faith.
Love, as intensely as we feel it today, and as much attention as it receives in popular culture, art, and daily conversation, would seem the least important of these, a titillating but nonadaptive neurochemical high similar to the one we get from cocaine, marijuana, a fine Château Margaux, or a good double espresso. If love is viewed only narrowly as romantic love, then it is probably not a cornerstone in the creation of human nature. But love in its larger sense—the sweeping, selfless commitment to another person, group, or idea—is the most important cornerstone of a civilized society. It may not have been important for the survival of our species as hunter-gatherers and nomads, but it was essential for the establishment of what we think of today as human society, what we regard as our fundamental nature. Love of others and of ideals allowed for the creation of systems of courts, justice that is meted out to all members of society equally (without regard to financial status or race), welfare for the poor, education. These fixtures of contemporary society are expensive in terms of time and resources; they work because we believe in them, and are willing to give up personal gain to support them.
I mentioned “I Walk the Line” as an example of a knowledge song, because the singer is reminding himself to “toe the line,” to be true. But of course, it is also a powerful love song, a song celebrating a commitment to something above the passing emotions of lust.
Our love for another person, that special someone, a single love interest, pulls us out of ourselves and lifts our thoughts to a grander scale: How can I make the world better for this person? When I was in my twenties, the only love I experienced was the immature, selfish love of “I love her because she makes me feel good. I want to make her happy so that she’ll stay with me.” Now, at fifty, I think about the woman I love in terms of what
she
wants. I want to make her happy because I can’t be happy when she is unhappy. We discover that the act of giving love is more powerful than getting the hug you need—if we can get over our own hunger for love, then we have reached the state of pure love, of being connected to a larger ideal, bigger than our own individual life.
she
wants. I want to make her happy because I can’t be happy when she is unhappy. We discover that the act of giving love is more powerful than getting the hug you need—if we can get over our own hunger for love, then we have reached the state of pure love, of being connected to a larger ideal, bigger than our own individual life.
Love songs, like all art, help us to articulate our feelings. They often use metaphorical language (“I’m on fire,” “I will climb the highest mountain”) to help us see our emotions from a different perspective. They stick in our heads to remind us, as the emotions ebb and flow, of what we once felt. And above all, they raise the feelings to the level of artistic expression—imbuing them with an elegance and sophistication that helps us strive for them even when the going gets tough.
To understand where love songs came from, it is necessary to go back in evolutionary history and ask two questions. First, of all the senses that could do this work, why does
sound
have such an important role in our emotions (or, in other words, what are the evolutionary origins of hearing and music)? Second, how did the evolutionary changes that gave us the musical brain give us the sort of consciousness that is required to compose songs, to create art and science, and to build functioning societies?
sound
have such an important role in our emotions (or, in other words, what are the evolutionary origins of hearing and music)? Second, how did the evolutionary changes that gave us the musical brain give us the sort of consciousness that is required to compose songs, to create art and science, and to build functioning societies?
The hair cells that we have in our ears are found in all vertebrates, including fish, and are structurally and functionally similar to those found on the legs and bodies of many insects (where they are called
sensilla
). When a grasshopper moves its leg, its hair cells are stretched and help to indicate the position and location of the leg. They are also sensitive to air, water, and other currents, to help detect the presence of an object approaching. This points to the phylogenetically early use of hair cells not just for detecting changes in pressure, which led to hearing in mammals and fish, but changes of position, which led to the vestibular system, our sense of balance. Hair cells are so sensitive that a stretching or movement of only 100 picometers causes them to fire—that’s 1/100,000,000 millimeters, or 100,000 times smaller than a chromosome and 10 times smaller than the radius of a hydrogen atom.
sensilla
). When a grasshopper moves its leg, its hair cells are stretched and help to indicate the position and location of the leg. They are also sensitive to air, water, and other currents, to help detect the presence of an object approaching. This points to the phylogenetically early use of hair cells not just for detecting changes in pressure, which led to hearing in mammals and fish, but changes of position, which led to the vestibular system, our sense of balance. Hair cells are so sensitive that a stretching or movement of only 100 picometers causes them to fire—that’s 1/100,000,000 millimeters, or 100,000 times smaller than a chromosome and 10 times smaller than the radius of a hydrogen atom.
The eardrum is a thin membrane stretched out taut inside our ears, and changes in pressure—whether in air, water, or another medium—cause it to wiggle in and out. This pattern of wiggling eventually sends signals to a snail-shaped organ in the inner ear called the cochlea, which is lined with hair cells much like insects’ sensilla. The human cochlea is so sensitive that it can detect vibration as small as the diameter of an atom (0.3 nm ) and it can resolve time intervals down to 10μs—if a sound ten feet away from you moves even two-and-a-half inches to one side, you can detect that movement just by the difference in the sound’s arrival time at your two ears. The ear detects energy levels a hundredfold lower than the energy of a single photon. Hearing is so sensitive that some species can hear the footsteps of the insects that they seek to eat.
The advantage of hearing over other senses, such as vision for example (as I mentioned in Chapter 2) is that sound transmits in the dark, travels around corners, and can reach us when there are visual obstacles between us and what we want to hear. Sound constitutes an effective early warning system for something approaching us—a boulder rolling uncontrollably down a hillside, a predator stepping on a twig outside our cave, and so on. As part of the early warning system, our hearing sense also has immediate neural connections to our startle response, and detects even the slightest change in background noise in the environment.
Evolution might well have found
other
ways for us to gather information about the environment rather than the senses we know. Indeed, some animals employ systems that are exotic compared to ours. Sharks have an
electrical
sense—a sensory system that detects electrical fields produced by the neuromuscular activity of potential prey. Bees, ants, turtles, salmon, sharks, and whales use a magnetic sense for orientation. Indigo buntings possess a celestial compass that allows them to fly at night to find north; through evolution, they have internalized the fact that the entire sky revolves around Polaris, and so they navigate based on the one star that doesn’t change position in the night sky. Interestingly, bunting genes don’t specify which star is the North Star, only that the invariant star should be treated as north (allowing for the possibility that buntings could navigate throughout the northern hemisphere without having to develop a separate mechanism for different latitudes). Experiments by Stephen Emlen with indigo buntings in a planetarium demonstrated that the birds will treat any star as the reference point if it stays stationary.
other
ways for us to gather information about the environment rather than the senses we know. Indeed, some animals employ systems that are exotic compared to ours. Sharks have an
electrical
sense—a sensory system that detects electrical fields produced by the neuromuscular activity of potential prey. Bees, ants, turtles, salmon, sharks, and whales use a magnetic sense for orientation. Indigo buntings possess a celestial compass that allows them to fly at night to find north; through evolution, they have internalized the fact that the entire sky revolves around Polaris, and so they navigate based on the one star that doesn’t change position in the night sky. Interestingly, bunting genes don’t specify which star is the North Star, only that the invariant star should be treated as north (allowing for the possibility that buntings could navigate throughout the northern hemisphere without having to develop a separate mechanism for different latitudes). Experiments by Stephen Emlen with indigo buntings in a planetarium demonstrated that the birds will treat any star as the reference point if it stays stationary.
Given that evolution gave all vertebrates a sense of hearing, it isn’t obvious that this would develop into something as complex as music, but evolution moves slowly. Complexity is built up stone by genetic stone through small adaptations, each in itself perhaps imperceptible, building to a grand crescendo. As hearing became refined, and responsive to environmental events, selection pressures made all vertebrate brains sensitive to differences in pitch, spatial location, loudness, timbre, and rhythm, the fundamental ways in which objects can be differentiated from one another through sound. This is not so surprising, because the basic structure of neurons and synapses, the chemical soup of neurotransmitters, is common to all vertebrates.
The basic function and structure of genes is also common to all animals. Genes serve to determine, constrain, and guide cells so that they develop properly and perform their essential functions; they contain instructions, like a blueprint, that neurons and other cells follow. As fetal and infant brains develop, certain common proteins encoded in DNA, such as netrins and homoetic gene products, even dictate how neurons will connect with one another along specific pathways that are analogous in animals as different as roundworms, insects, birds, and mammals. The genetic instructions for neural development are both so powerful and so flexible that they can even guide neural connections to the right places when part of one brain is transplanted into another. Evan Balaban removed the auditory cortices from Japanese quail embryos and surgically implanted them into the brains of embryonic chickens. Not only do the grafts link up anatomically with the new host brains, but the host birds act in ways that demonstrate they have incorporated the donors’ hardwired propensities—specifically, the chickens make vocalizations like quails, not like chickens, even when they are raised by other chickens.
Auditory pathways that are comparable to ours exist even in reptiles and birds. One interesting similarity of auditory system architecture is
tonotopy.
This means that frequency-selective neurons in the auditory cortex are configured so that low notes activate one end of it and high notes the other—the cortex is literally laid out like a piano keyboard! Tonotopy has been seen in the guinea pig, squirrel, opossum, ferret, tree shrew, marmoset, owl monkey, macaque monkey, rabbit, cat, and bush baby, plus many reptiles and birds. But even though these animals and humans share such tonotopic organization, there remains disagreement among researchers about animals’ ability to differentiate pitches. It is clear that they can distinguish low tones from high tones, but as tones get closer together, it seems that many animals don’t possess the same resolution that humans do: Three consecutive tones in our musical scale may all sound like the same tone to a marmoset, frog, or carp.
tonotopy.
This means that frequency-selective neurons in the auditory cortex are configured so that low notes activate one end of it and high notes the other—the cortex is literally laid out like a piano keyboard! Tonotopy has been seen in the guinea pig, squirrel, opossum, ferret, tree shrew, marmoset, owl monkey, macaque monkey, rabbit, cat, and bush baby, plus many reptiles and birds. But even though these animals and humans share such tonotopic organization, there remains disagreement among researchers about animals’ ability to differentiate pitches. It is clear that they can distinguish low tones from high tones, but as tones get closer together, it seems that many animals don’t possess the same resolution that humans do: Three consecutive tones in our musical scale may all sound like the same tone to a marmoset, frog, or carp.
In all these species, however, the ability to locate a sound in space is highly evolved—neurons take projections from the two ears to indicate where the sound is coming from. The reason that stereo sounds so much better to most of us than mono isn’t just that different sounds come from two different places instead of one, but that evolution favored those species who developed and used stereophony for sound localization; we like stereo because we are descended from ancestors who exhibited a selective advantage for this form of spatial processing, one that helped us to better locate (and escape from) predators.
Differences across species in several brain regions (particularly in the thalamus and auditory cortex) led to differences in the ability to remember sounds and their locations. It takes many, many more trials for a rat to learn an association between a sound and an event (such as a source of food or danger) than it does for a cat; primates are even faster learners. Another difference is that the higher up one goes, so to speak, in the phylogenetic ladder, the longer are the latencies for neural firing and the lower are spontaneous discharges from auditory neurons. In other words, more advanced species are
less
likely to startle. This makes sense because we humans rely less on sound-by-itself to make sense of the world than do lower animals. We combine sonic information with information from other senses, with memories, and also expectations about what is going to occur. Expectational processing reaches its peak in humans—we can prepare ourselves for a loud noise as we see a pin approaching a balloon; the binturong and the baboon are more likely to be bothered by the burst, no matter how many times they see pin pop the balloon.
less
likely to startle. This makes sense because we humans rely less on sound-by-itself to make sense of the world than do lower animals. We combine sonic information with information from other senses, with memories, and also expectations about what is going to occur. Expectational processing reaches its peak in humans—we can prepare ourselves for a loud noise as we see a pin approaching a balloon; the binturong and the baboon are more likely to be bothered by the burst, no matter how many times they see pin pop the balloon.
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