Glossary

allometry Measured comparisons of two organs or organ-systems. In brain-body allometry, usually the regression of brain size on body size. Size is scaled logarithmically, and the allometric equation is usually a power function.

encephalization The degree to which actual brain size in a species is greater or less than that expected according to an allometric analysis. It is often measured as an "encephalization quotient'' (EQ), which is the residual of the regression of log brain size on log body size.

neocortex A characteristically layered portion of the cerebral cortex unique to mammals, usually six-layered.

There are about 50,000 species of vertebrates, each unique in many traits but sharing ''primitive'' traits with close and distant relatives. The pattern of unique traits defines each species, and the suite of shared (older, more primitive) traits, depending on the size of the suite, helps define them as members of a higher taxon:

This article is updated from one originally published in D. W. Zaidel, (Ed.), Neuropsychology. Academic Press, New York. (1994). For those with access to the Internet, an unusual collection of data is available for inspection and analysis at a site supported by the U.S. National Science Foundation, including photographs of brains and serial sections of brains in many living species of mammals. Fossil evidence is displayed at the same site and may be accessed at http:// www.neurophys.wisc.edu/brain/paleoneurology.html.

genus, family, etc. This is as true for neural traits as it is for other traits that differentiate animal species. All biologists accept the evolutionary dogma that the uniformities in traits across species are due either to common ancestry or to convergent evolution, and that the diversity of species should usually be explained by adaptations to specialized environmental niches.

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