from Applied Neuropsychology
Posted 08/09/2002

Abstract

Reading is not a "natural" human ability. Because reading was invented only 6,000 years ago there cannot have developed any central nervous system structures specifically for the purpose of mediating reading. The anthropological concept of preadaptation, which states that the evolution of a structure for one purpose can enable that structure to perform another, must be true for reading. The research discussed in this article looks into the functions that preadapted the brain for reading. Findings suggest that the ancient skills of gestural comprehension and animal tracking were the underpinnings of brain organization that permitted reading to occur.

Introduction

The five major components of aphasia assessment are fluency, word finding, repetition, aural comprehension, and reading comprehension. Of the five, reading is the "odd man out". That is, the first four are widely believed to have been human language capabilities for at least the last 2 or 3 million years, more than enough time for the development of brain structures to mediate these abilities.

Reading is completely different. It is a cultural, not an evolutionary development; that is, the alphabet was only invented 6,000 years ago and nearly every human on earth was illiterate until the 20th century. Thus, our capacity to read did not involve biological evolution; it involved cultural developments that were only acquired as "typical" human abilities within the last 200 years in Europe and America, and only after World War II in the rest of the world. Australian aborigines, who arguably had the least developed language culture, learned to read just as easily as children of fifth-generation readers in America. There is nothing to suggest evidence of evolution for the purpose of mediating reading in a general sense, and reading words for meaning after decoding the surface structure of written language in particular.

Yet still we can read, but it is not the same as speaking and understanding. Admittedly, any typical 4-year-old child has already mastered aural comprehension and speech just by spending time with people who already speak. However, it takes years of formal, daily education to produce a person fluent in reading. Thus, aural comprehension and reading comprehension are not twins, or perhaps not even distant cousins. One is a natural ability, easily acquired, backed by years of central nervous system (CNS) evolution. The other is a recent addition to human culture, and is mastered only by long-term training, and thus cannot have any CNS mediation by structures built specifically for that purpose.

So reading is possible, but still quite difficult. Modern neurolinguistics has barely begun to scratch the surface of understanding how reading works because the basic CNS structures that mediate reading were not specifically designed for reading (or any other language function). These structures were already fully developed in service of some other abilities, which must have been an essential part of the human behavioral repertoire given the amount of CNS tissue that appears to currently mediate the reading for comprehension process.

Thus, we have two clear questions: (a) What were the original functions of the CNS tissue that currently mediate reading for meaning and written word comprehension? and (b) How does this knowledge matter for understanding alexia in particular, and visual language processing in general?