Appendix

Why don’t monkeys have music?

Although animal behavior may seem quite different across species—such as human use of language, music, art, and science versus just about all other animals—primate brains and genes show a great deal of continuity.

A striking example comes from the macaque monkey, an Old World monkey genus that includes the rhesus. Macaques share 93 percent of their DNA with humans, and our common ancestor dates to about 20 million years ago. Neuroscientists Michael Petrides and Deepak Pandya conducted extensive studies comparing the macaque brain to the human brain, and the anatomical subdivisions of both are shown side-by-side in the figure on the following pages. Note the great similarity—each structure found in the human brain is also found in the macaque. The areas of particular interest are those that subserve the three components of the musical brain outlined in this book: perspective-taking, representation, and rearrangement. Crucial evolutionary changes that enabled the evolution of the musical brain in humans surely included those in the orbital and ventrolateral prefrontal cortex, areas 47/12, 46, 45, and 44 in the figures here, and possibly area 10. These regions are known to be involved in the representation of ideas and the maintenance of them in working memory—those things that you are thinking about at any given moment, whether or not they are in front of you.

View of the frontal portion of the left hemisphere of the human and macaque brains (the leftmost portion of each figure is the front of the brain, just behind the forehead; area 44 is beneath your temples). The circled numbers are Brodmann area numbers, a conventional way of referring to neural regions following the nineteenth-century German neurologist Korbinian Brodmann, whose subdividions of the human brain are widely used. The large tongue-shaped structure at the bottom of each figure is the anterior portion of the temporal lobe; the parietal and occipital lobes are not shown. Figure redrawn by Karle-Philip Zamor, based on M. Petrides and D. N. Pandya (2001).

Area 6, just behind 44, is part of the premotor cortex, and is involved in moving the lips, jaw, and tongue. Petrides draws attention to the brain region that sits between the representing part of the brain and the oral-facial muscle planning part of the brain. During 20 million years of evolution, it is not too difficult to imagine a new function evolving right here where these regions meet, gradually enabling the brain to report what it is holding in consciousness—to start talking or singing about what it is thinking about. We now know that areas 44 and 45 (Broca’s area), as well as 47/12, are intimately connected with speaking and understanding speech, and with playing and understanding music in humans.

Why, then, haven’t monkeys developed speech or music? Part of the reason is no doubt physiological—the higher position of their larynx doesn’t give them the fine motor control necessary to produce the variety of speech sounds that give human language its combinatorial power and hence its richness (Lieberman and Patel). If you are wondering why parrots can make such rich sounds, it is because they evolved a completely separate form of vocal organ, the syrinx, that allows them to mimic some of the sounds of human speech (see, e.g., Larson and Goller). Yet if the dearth of monkey talking and singing was merely a production limitation, we’d expect them to be able to learn to recognize music (and speech), perhaps to develop musical listening preferences, but researchers have found no evidence of this. There is a cognitive, not simply a motor limitation; they just don’t get it. Petrides and Pandya and others have argued that a key difference is not in the gross structure of the brain, but in the fine structure. The human brain evolved to have far many more folds and convolutions than the macaque brain, making it possible to squeeze millions of more neurons into a relatively confined space. Moreover, and partly as a consequence of the greater neural density, human brains have a great deal more connectivity—regions of the human prefrontal cortex are more elaborately connected, and they connect bidirectionally with many other regions evolved in thought and emotion: the hippocampus, amygdala, association cortex, and limbic system to name a few. A controversial new idea is that higher cognitive operations such as music are an emergent property of the complexity of the system as a whole. In other words, there is no one device that was plugged in to create the musical brain; the whole brain had to change in terms of information processing. Monkeys don’t have music and speech because, although the skeletal architecture is there, the raw computational power is not.

Larson, O. N., and F. Goller (2002). “Direct observation of syringeal muscle function in songbirds and a parrot.” Journal of Experimental Biology, 205: 25–35.

Lieberman, P. (1984). The Biology and Evolution of Language. Cambridge, MA: Harvard University Press.

Patel, A. D. (2008). ibid.

Petrides, M. and D. N. Pandya (2001). “Comparative cytoarchitectonic analysis of the human and the macaque ventrolateral prefrontal cortex and corticocortical connection patterns in the monkey.” European Journal of Neuroscience, 16: 291–310.