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Krasnow Institute > Monday Seminars > Abstracts
Evolutionary Origins of the Vertebrate Mind Ann B. Butler What is my mind and where did it come from? Recent advances in the field of comparative neuroanatomy have allowed for the identification of several dramatic and seminal changes that occurred in the central nervous system with the evolutionary origin of vertebrates and produced the basic framework of the vertebrate brain. It has long been believed that the earliest vertebrates were tiny creatures with only a spinal cord and hindbrain-like central nervous system, able only to reflexly react to any stimuli in their environment, and that their lifestyle was a relatively sedentary and passive one. Newly acquired evidence suggests, on the contrary, that a forebrain--which in humans includes the cerebral cortex and the nuclei that relay sensory information to it--was present in the earliest vertebrates. The sensory information processed in the forebrain allowed these earliest vertebrates to assess the condition of their environment and to be actively mobile predators within it. Also gained at the same time were new tissues that produce many of the sensory components of the nervous system, allowing for a much greater degree of information content and of resolution in the inputs from multiple sensory systems. Subsequently, significant evolutionary variation has occurred in brain organization within the various lineages; among the most pronounced changes that have occurred independently in several different lineages, is a major expansion of the forebrain. Clearly, expanded capacity for sensory processing, for storage of information, and for assessment of that information in comparison with the situation of the present is a trait that is markedly favored by natural selection. With the origin of amniote vertebrates (mammals, reptiles, and birds), new sensory input pathways to the cerebral cortical areas were gained, and previously present ones were expanded. The origin of mammals was characterized by a number of key changes: 1) a major expansion of the body's sensory system of touch occurred with the development of hair and its delicate sensory capacities; 2) major expansion of the motor system occurred with the challenges of survival on the varying terrain of a land-based environment, 3) a major expansion and a new, "radial" organization occurred in the cerebral cortex that provided for greatly enhanced detail and also a much greater capacity of sensory processing, and 4) the particular sensory system pathways that feed into areas related to visual, body-sensory, and memory storage cerebral areas were greatly expanded. Among mammals, primates have relatively large cerebral cortices, and, among primates, humans have capitalized on one particular trait--that of expansion of cerebral cortical areas for understanding and for producing vocal (or vocal-related, symbolic) communication. To make a long abstract short: we humans are who and what we are from 1) having become active, aggressive, and mobile predators with new sensory information input and processing to guide us, 2) having greatly expanded the senses of touch and vision, and 3) having gained the ability to speak. Our cognitive abilities, our conscious perception of ourselves and of our world, and the phenomenon that we call "mind," are all based on this foundation and derived from it.
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