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  3. The human brain is somewhat like an archaeological site, preserving within its layers the basic brain structures of its evolutio

The human brain is somewhat like an archaeological site, preserving within its layers the basic brain structures of its evolutio

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问题     The human brain is somewhat like an archaeological site, preserving within its layers the basic brain structures of its evolutionary predecessors— the lower mammals and reptiles (爬行动物). Consequently, it has a relatively recent outer layer that is distinctly primate (灵长目动物的), with special developments and tissues that distinguish human beings from other primates. Nevertheless, we have not one brain, but at least three—that is, three connected parts carry out distinctive but interrelated functions.
    The oldest part of the human brain is the "reptilian brain," which is found in the lower center of the brain. It resembles a basic part of the brain of reptiles and serves many of the same functions in humans that it serves in reptiles. It regulates a large number of innate behavior patterns that are related to preserving the species.
    During the course of evolution, a new formation of brain cells, developed in lower mammals giving them two brains. This ancient, mammal brain adds new things to the behavior repertoire (全部功能) of mammals. The business of this new brain is basically the desires and emotions that keep mammals moving, mating, and avoiding pain. For many mammals, evolution stopped here.
    The brain continued to develop with the addition of a third layer called the "neocortex" (新皮层). This new part of the brain reached its peak of development in human beings. This is the brain that gives humans the capacity of rational thought. Because of the new part of the brain we are able to en gage in verbal communication, to read and write, to empathize (表同情) with others, and to contemplate our own existence.
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答案the script of a television program produced for science students
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