Brain Organization:Diversity
Although the uniformities are impressive,diversity among species with
respect to their brains is even more compelling.It is not possible to
convey its scope in this short chapter.The pages of major technical jour-
nals,such as Brain,Behavior and Evolution,Journal of Comparative
Neurology,and Zeitschrift für Hirnforschungare filled with evidence.
I recommend one text on the subject,Butler and Hodos (1996),that
outlines the extent to which vertebrate brains are both similar to and
different from one another.Readers with access by computer to the
Internet may get an even better sense of diversity,at least in mammals,
at http://www.neurophys.wisc.edu/brain/.Here one can see pictures of
whole brains and of histological sections,accompanied by narratives
relating brain to behavior in dozens of mammals,and thus have an easy
introduction to the diversity of living species.
The relationship between uniformity and diversity is a kind of forest-
and-trees problem.Uniformities enable one to view general features of
the organization of brains,but when they are examined more closely,one
is also impressed by the variety of specializations among species and of
the parts of the brain.Furthermore,there are levels of organization.The
size of the brain as a whole,at least in mammals,provides a measure of
the total information-processing capacity that evolved in a species,as
shown in figure 12.3.But the information must be broken down to be
analyzed,and such analysis is performed hierarchically by specialized
regions.
We are reasonably certain that some perceptual activity is indeed
common to various species.Although we enjoy speculative excursions
into the perceptual worlds,or Umwelten,of other species,emphasizing
specific specializations (von Uexküll 1934;Jerison 1986),we have good
reason to assume that in most vital features the world as experienced is
stable among species;that is,their experienced worlds are similar.But
we also see dramatic differences in the way distance-senses work and in
the kind of information available to animals of different species about
events at a distance.
Sensitivity to pure tones in mammals has been well understood for
some time.Among cats and dogs,the upper limit of sensitivity extends
about two octaves above the human upper limit to about 60kHz,com-
pared with a human maximum of about 20kHz.Maximum sensitivity is
also shifted upward by an octave from about 3kHz in humans.Mice and
rats,on the other hand,have their peak sensitivity shifted upward about
two octaves to about 8kHz and an upper limit of sensitivity to over
100 kHz.It is surprising that dolphins are comparable with rodents in this187 Paleoneurology and the Biology of Music