Harry Jerison

Abstract

Paleoneurology, the study of fossil “brains,” provides direct evidence about the

500-million-year history of the vertebrate brain. Analyzing changes in the exter-

nal appearance of the brain as mirrored in casts molded by the cranial cavity,

paleoneurology relates evolutionary changes in the brain to the evolution of

behavior and of the capacity to perceive and know an external world. For any

behavior, questions of evolutionary antecedents and relationships arise. The

relevance of paleoneurology for our understanding of the evolution of human

musical expression and experience lies in the relationship of these traits to gross

features of brains. From present evidence, it may be especially important to seek

connections with language rather than with nonlinguistic acoustic phenomena in

other species, even when, to the human ear, the phenomena have an obviously

musical dimension. We know that in mammals and birds, increases in the brain’s

capacity evolved to process information about the external world, a capacity

related to the evolution of increased perceptual and cognitive capacity. The

genetic blueprint for a brain to develop this intelligence-creating capacity is actu-

ally an epigenetic blueprint requiring a normal environment for the growth and

development of the nervous system. In their fundamental biology, therefore,

brain and intelligence result from a nature-nurture interaction. Different intelli-

gences (in the plural) evolved in different species, depending on their neural

specializations, and the human variety derives mainly from the evolution of

language. It is this diversity of specializations that must be analyzed for an

understanding of the evolution of human musicality, which is in many ways an

adaptation within this specialized cognitive capacity.

Although my evolutionary work is with fossil brains, to show its rela-

tionship to the evolution of musical experience and expression I have to

emphasize information about brain and behavior in living species. One

must rely on such information for a proper perspective in all studies of

fossils. Let me explain that perspective.

My primary research material is fossilized evidence of the brain in ver-

tebrates, which is in the form of castings, endocasts, molded by the cranial

cavity. Several hundred fossil endocasts are known, and they provide the

most direct evidence of the brain’s evolution (Jerison 1973). In living

birds and mammals, they provide accurate pictures of the external

surface of freshly dissected brains. This enables one to treat endocasts as

if they were brains in which one can determine relationships between

the external anatomy of the brain and its functions in controlling behav-

ior and experience. To extend this to fossils, one relies on the classic uni-

formitarian hypothesis (Simpson 1970), which states that relationships

true for living species were also true for fossils. With respect to external

anatomy, endocasts from fossils are, therefore, truly fossil brains.

In analyzing fossil brains, I am necessarily limited to gross anatomy,

and this in turn limits me to very general categories of behavior. These

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Paleoneurology and the Biology of Music