Hypothesis: Phylogenetic diseases of the nervous system.

A few human diseases may be viewed from a phylogenetic perspective. Some metabolic or degenerative diseases selectively affect recently evolved or exclusively mammalian structures of the brain and spare the older structures. Examples include Krabbe's leukodystrophy, olivopontocerebellar atrophy, Friedreich's ataxia, Pick's disease, and Leber's optic atrophy. Some pathologic conditions in man are similar to normal anatomy in other species, although the mechanisms may differ. Congenital muscle fiber-type disproportion in rodents, Dandy-Walker cyst in birds, and agenesis of the corpus callosum in marsupials are representative of this category. Loss of basal dendritic spines from pyramidal cells in Pick's disease is reminiscent of certain large neurons normally found in the cortex of reptiles. Changes in metabolism in the evolution of mammals in general and of man in particular may explain some aspects of 'phylogenetic diseases'. Some potential examples are the shift from predominantly phospholipids to galactolipids in myelin composition as mammals evolved, and the greater toxicity of cyanide and other poisons of oxidative metabolism in mammals than in other vertebrates because of less reliance on anaerobic metabolism as an alternative energy source.