The Origins of Music: Preface - Preface

one another,following the rule of the equation of the best-fitting line

that is drawn in the graph.

This does not mean that brains are alike in every way.Rather,it means

in general that if evolutionary forces resulted in an enlarged brain,it is

the brain as a whole that tends to become enlarged,and the sizes of its

parts tend to be appropriate for the size of the whole.Neurologically,

this makes good sense.The brain’s parts work together.If one has an

enlarged motor neocortex,other parts of the brain that tend to work with

motor cortex must be appropriately enlarged,such as cerebellum and

basal ganglia.

The most outstanding example of uniformity in brain structure rela-

tive to function is the relationship between the surface area of the cortex

and gross brain size.This is illustrated in figure 12.3 for fifty species of

mammals (more detailed citations for the data in the figure,which

were collected in several different laboratories,are in Jerison 1991).

The species are from the orders Monotremata,Marsupialia,Artio-

dactyla,Carnivora,Cetacea,Insectivora,Perissodactyla,Primates,and

Xenarthra.As is evident,a single rule governs essentially all covariation

of cortical surface area and gross brain size in living mammals.Data on

twenty-three humans and thirteen dolphins that were available for this

graphical analysis are enclosed in small convex polygons near the fitted

185 Paleoneurology and the Biology of Music

Figure 12.3

The relationship between cortical surface and gross brain size in fifty species of mammals.

Each point represents a species.In addition,two labeled minimum convex polygons

indicate within-species variability in twenty-three humans and thirteen dolphins (Tursiops

truncatus).Several species are labeled to indicate the diversity of the sample.(From Jerison

1991,by permission.)

Fig.12.3