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frontal lobe。 Although Broca was unable to conduct ablations on his patients； at the autopsies following
their deaths； he repeatedly found an injury to the same area of the brain in those patients who had
manifested difficulty in the production of speech。 His work was eventually connected to that of Karl
Wernicke； who found a similar area in the left temporal lobe and observed that trauma to this area resulted
in poor prehension of speech。 Taken together； we now refer to the areas pinpointed by Broca and
Wernicke as the “language center” of the brain。 Individually； we refer to these areas as Broca’s area and
Wernicke’s area。
Neuroglial Cells： The Glue of Life
The term glia is derived from the Greek word for glue and is an appropriate name for the cells that surround
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CHAPTER3： THE BIOLOGICAL BASES OF BEHAVIOR
all neurons； sealing them together。 Glial cells outnumber neurons ten to one； and； though tiny in size； make
up half of the bulk of the brain。 Unlike neurons； glia do not possess excitable membranes and so cannot
transmit information。 Glia can take up； manufacture； and release chemical transmitters； and in so doing
may help to maintain or regulate synaptic transmission。 Another hypothesis is that glia can manufacture
and possibly transmit other kinds of molecules； such as proteins。 The anatomy of some glial cells is striking
in this regard； for they seem to form a conduit between blood vessels and neurons； and may bring
nourishment to the neurons。 It is thought that these cells may have important functions during prenatal
development and recovery from brain injury。 One role of glia is known definitely： Certain kinds of glia；
called by the tongue…twisting name of oligodendroglia； form the myelin sheath that insulates axons and
speeds conduction of the nerve impulse。 A counterpart called a schwann cell performs the same role for the
peripheral nerves。
The study of glia is difficult because these tiny cells are inextricably entwined with neurons。 As the most
numerous type of cell in the brain； their potential importance is vast； and investigation of their function
seems likely to yield exciting results in the near future。
Charles Darwin and Natural Selection： A Taproot of Contemporary
Psychology
Charles Darwin； and his theory of natural selection； had a greater impact on the development of modern
psychology than anyone else； and continues to have a profound effect on all of the natural sciences。 Natural
selection is the one assumption with which most natural scientists agree； although its exact mechanisms
may be disputed。 Darwin； a naturalist； published his theory of evolution in a book entitled On the Origin of
the Species by Natural Selection in 1859； about 20 years before the birth of experimental psychology。
Darwin’s ideas have shaped contemporary psychology in the following ways：
1。 Continuity between Animals and Humans。 This idea was difficult for society to accept； because
humans assumed that they were the crowning glory of creation and not subject to the natural laws
as were members of the animal kingdom。 Even those scientists who applauded Darwin’s theory
had some difficulty in accepting the idea that evolution applied to humankind。
2。 Individual Differences。 The various members of a given species may have many characteristics in
mon； but there are also differences among those members—individuals—that can determine
whether the “fitness” of their offspring will enable them to pete successfully in the battle for
survival。
3。 The Importance of Adaptability。 Survival depends on the ability of an organism to adapt to the
environment and to changes in that environment。 Failure to adapt means extinction。 Ninety…nine
percent of all organisms that have even lived on earth are already extinct。
4。 The Importance of the Environment。 The surrounding environment changes； over time； and
“fitness” means making the various physical and behavioral changes that are appropriate for
survival。
5。 Emphasis on Change。 Before evolutionary theory； the monly held view was that the earth and its
inhabitants were immutable and static。 Darwin’s portrayal of nature is dynamic； mutable； and
interacting。
Darwin’s ideas influenced many psychologists； including Freud； Watson； Skinner； and James。 The most
apparent legacy from Darwin to Freud’s theory was the idea of the continuity of animals and humans。
Freud thought humans were driven by the same instincts that motivate other animals—instincts to survive
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PSYCHOLOGY AND LIFE
and reproduce。 According to Freud； people have no inherently higher nature than do animals； and
whatever in humans may be higher （sympathy； altruism； unselfishness） is a product of the processes of
repression and reasoning。 In Freud’s perspective； the dominant force in the structure of personality is the id
（the representation of the instincts for survival and reproduction）； but humans develop other aspects of
personality to control these instincts in order to adapt to munal lifestyles。 munal living is
important in terms of adaptive behavior for humans because humans are rather weak creatures pared to
the large predators。
The idea of continuity between animals and humans also influenced the behaviorist theories of Watson and
Skinner。 Watson began his career as an animal psychologist believing； as later did Skinner； that the basic
principles of behavior can be discovered by studying the behavior of animals。 Though behaviorists do not
deny individual differences in genetic endowment； they do tend to place greater emphasis on
environmental determinants of behavior。 Skinner emphasized learning rather than innate factors as being
the antecedent of behavior； believing that through a process of trial and error； organisms learn which
behaviors lead to reinforcement…things that ensure survival and reproduction…and which behaviors are
futile； and are followed by loss or punishment。 Thus； according to behaviorists； learning is our primary tool
for adaptation； and it is the environment that shapes behavior； rather than “mind” or “consciousness”
within the organism。
Behaviorism also emphasizes change。 Both Watson and Skinner suggested that a utopian society could be
built by imposing proper control on environmental conditions。 Emphasis on change is one of the hallmarks
of our society； we are convinced that we can be better； thinner； smarter； richer； and happier。 Psychologists
have been in the forefront in convincing us that change is possible； though not necessarily easy。
The idea of adaptation to the environment was the central Darwinian theme in the functionalism of William
James and the originators of the functionalist approach。 Human behavior （James used the term “habits”）
was considered in terms of how it served the goal of adaptation。 Like the behaviorists； the functionalists
saw learning as the primary mechanism for human adaptation and survival。
A precursor of functionalism was the British intellectual giant； Sir Francis Galton。 Using Darwin’s theory；
Galton developed a keen interest in individual differences and strived to devise ways to measure these
differences。 American psychologists eagerly adopted his ideas； with their emphasis on individualism。
Psychological testing developed from this facet of functionalism and continues to be an active area in
American psychology。 We have developed psychological tests to measure almost any trait you can imagine。
Ironically； the founder of psychology as a science； Wilhelm Wundt； was not significantly influenced by
Darwin’s theory； and when Wundt’s branch of psychology； structuralism； migrated to America； it was
unable to adapt and survive。
BIOGRAPHICAL PROFILES
Rene Descartes （1596—1650）
Born of wealthy parents in La Haye； France； Descartes was one of the most influential thinkers of the
Renaissance。 He contributed to mathematics； philosophy； psychology； and physiology。 Descartes； a very
private man； enjoyed solitude and was iconoclastic。 While enrolled at a Jesuit school； he convinced the
school authorities to allow him to sleep until 11 A。M。； because he did his best thinking while in bed。
Perhaps because of this individualistic nature； Descartes began to doubt all that he had learned in school。
This skepticism soon spread to all areas of his life。 Descartes doubted everything。 Of one thing； however；
Descartes had no doubt： that he was doubting。 This led to his famous conclusion； “Cogito； ergo sum。” “I
think； therefore I am”； which suggests that all that is certain concerning the human condition is that each of
us exists。 Descartes also made significant contributions to physiology。 He believed that what distinguished
living from nonliving material was “animal spirits”。 Animal spirits； according to Descartes； gave humans
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CHAPTER3： THE BIOLOGICAL BASES OF BEHAVIOR
their ability to move and worked mechanically； like hydraulics。 Although his notion of animal spirits has
been shown incorrect； his study of both animals and humans paved the way for future discoveries。
Descartes also addressed the mind—body