Ninth Edition CoverGraziano & Raulin
Research Methods (9th edition)

The Impact of the Darwin-Wallace
Theory of Evolution by Natural Selection


As happens often in science, important discoveries may be made simultaneously and independently by different researchers working from similar theoretical perspectives. Charles Darwin (1809-1882) was one of the most important scientists in history. His work, On the origins of species by means of natural selection (1859) has had profound effects on science, philosophy, religion, and even on political debates.

After completing his famous journeys, Darwin spent the next 21 years (1838-1859) in England, refining his ideas for publication. In June, 1858, when his book was still far from completion, Darwin received a manuscript in the mail in which his own thesis had already been written. Darwin had been preempted by another naturalist, Alfred Russel Wallace (1823-1913).

According to Arthur Keith (1954), Wallace traveled and studied in the Amazon valley and in the South Pacific as Darwin had done many years before. Wallace was impressed by the diversity of life he found there, and he followed, completely independently, the same line of reasoning as Darwin in making sense out of the observed data. The result was Wallace's manuscript on the biological operation of natural selection in the origins of new species. Wallace mailed his discovery to Darwin for comment.

Who was to be the first to present this momentous discovery to the world? Darwin's associates arranged to have the work presented simultaneously at a meeting of the Linnean Society of London on July 1, 1858. Thus, Wallace and Darwin are credited equally with the discovery. 

The Greeks had developed concepts of evolution over 2000 years earlier. However, it was Wallace and Darwin who gathered the mass of data and presented the concept of natural selection as the mechanism for how evolution works. During the following year, Darwin completed On the origins of species and soon became the acknowledged originator of this modern theory of evolution. Wallace, apparently content with this, made no great efforts to share in the subsequent acclaim, and the two men remained lifelong friends. Wallace made many other important contributions to science and is recognized by biologists as an eminent naturalist. However, it is Darwin who is remembered for this great biological discovery.

The Darwin-Wallace Theory of Biological Evolution by Means of Natural Selection

Charles R. Darwin (1809 –1882) was the naturalist on the HMS Beagle in the English government's globe-circling expedition (1831-1836). He made thousands of observations on climate and weather patterns, geological formations, fossils, plant and animal life, and collected and studied a large number of specimens. Darwin observed that within each species there are many variations in structure, some minute, others large. He wondered why, if a species is created as one, should there be so much variability among its individuals? This observation of variability within species was to become a major concept in his later work on biological evolution through natural selection.

From 1846 to 1858, Alfred Russel Wallace carried out naturalistic studies on the Amazon and the Malay islands. His observations and inferences were strikingly similar to Darwin's. Wallace, too, observed intra-species variability from which he independently formulated the concept of evolution through natural selection.

It is interesting that both men had been strongly influenced by the work of the economist Thomas R. Malthus (1766 - 1834), who had published An essay on the principle of population in 1798. In that essay, Malthus suggested that human population size naturally increases beyond the limits of resources needed to sustain it. He reasoned that the human condition will gradually worsen as populations grow and individuals compete more strenuously for increasingly scarce goods. A rapidly increasing population, according to Malthus, is not tenable and will be checked by natural occurrences, such as famine, disease, and warfare. As we will see, the Darwin-Wallace concept of natural selection is similar to Malthus' speculations about the relationship of population size, available resources, and competition.

We can summarize the Darwin-Wallace theory of biological evolution by means of natural selection as follows:

  • Within each species, many more individuals are produced than can be supported by nature's limited resources;
  • There is, thus, a natural struggle for survival;
  • Within each species there are many spontaneous variations;
  • Some of the variations are more useful than are others in helping the organism to adapt to environmental conditions;
  • Those useful adaptive variations are likely to survive and to be transmitted to the next generation through normal inheritance;
  • It is the slow accumulation of these minute variations over very long time periods that results in the extinction of old forms and the emergence of new species.

Thus, for Darwin and Wallace, evolution is a constant biological process that operates very slowly through the natural selection of minute intra-species variations in the continual struggle for existence. It must be noted that Darwin and Wallace viewed the variations as arising by chance, and not, as Lamarck had earlier speculated, (see below) through effort or design. Also, their model was not an attempt to explain the creation of life, as so many critics seem to think. Rather it is an attempt to understand the development of new species from original forms.

Precursors to the Darwin-Wallace Model

The impact of the Darwin-Wallace model on culture in general, and on science in particular, has been immense, but not because the concepts were especially original! The concept of the evolution of organisms from relatively simpler life in the seas to more complex sea and land forms had been developed in Greece from 600-300 B.C. by philosophers such as Thales, Anaximander, and Aristotle. In the 4th Century A.D., Saint Augustine interpreted the Biblical account in Genesis as meaning that God created the first living thing and endowed it with the power to evolve into other forms. This is still an accepted idea among many theologians. Indeed it is the current basis for attempts to reconcile the account of Genesis and that of Darwin-Wallace.

The development of the microscope in the 17th Century and the biological classification system of Linnaeus in the 18th Century spurred the accumulation of biological data that supported various concepts of evolution. In 1794, Darwin's grandfather, Erasmus Darwin, wrote that all warm-blooded animals might have developed from some common, earlier forms. In 1802, the naturalist Jean de Lamarck proposed a theory of biological evolution that, in general, is similar to the later Darwin-Wallace model, but differs because Lamarck's model included a purposive element. Lamarck believed that individuals changed to meet changing conditions and then passed on these acquired characteristics through inheritance to the next generation.

In the 19th Century, prior to the publication of the Origin of species, philosophers and social thinkers like Hegel, Comte, Marx, and Spencer, had already taken ideas about evolution seriously and applied them to their analyses of history and society.

It was not only the evolutionary concept that had been developed earlier, but also the idea of natural selection. According to Hofstadter (1948), Darwin noted that the natural selection concept had been "distinctly recognized" by W. C. Wells in 1813, and discussed by the botanist Patric Matthew in 1831. Hofstadter commented, "The general idea of organic change, as well as the particular organic concept of natural selection and the struggle for existence, was in the air; there is less question how vital thinkers and scholars came to be affected by it as how they could have avoided it" (1948, p. 124).

As is the case in all of science, many researchers work independently and contribute to the web of concepts and facts that make possible the next great development in the field. This seems to have been the case in 1859 when the Origin of species appeared. Scientists generally had no difficulties with the concepts, because, they were already familiar with them by then. The scientific world was ready for the ideas of Darwin and Wallace.

The Two Major Contributions of the Darwin-Wallace Model

Given this prepared world, the Darwin-Wallace model was highly visible and had an enormous impact. Scientists were already familiar with the concept of biological evolution. What they did not have was a critical mass of compelling empirical data to support the theory, and a credible explanation of the mechanisms through which evolution operates. The Darwin-Wallace model provided both of these to the receptive scientific world. They provided (1) the enormous wealth of carefully obtained and organized biological data to buttress their theories and (2) a clear exposition of a mechanism (i.e., natural selection) by which the process of evolution might operate. With these, scientists in many disciplines now had the conceptual tools to move ahead in an astonishing array of newly stimulated research and theorizing.

The Religious Response

It must be remembered that in 1800, nearly all persons in the Western world, including many scientists, believed that the world and all life had been created in six days just a few thousand years earlier, and that all life was still in its original form. By 1859, when the Origin of Species was published, it was generally welcomed by scientists of the time. However, it aroused ferocious protests from theologians, because it was immediately viewed as a direct attack upon the account of creation in Genesis. As one historian noted, the theory of the evolutionary origin of species "took the world by storm" (Boring, 1950, p. 470), creating immediate protests, and violently shaking the earlier religious dogma about human origins. Many attempts were made in newspaper editorials and cartoons and by public speakers and clergymen to belittle, discredit, and destroy the ideas. 

A noteworthy legal action taken to squash the ideas was the famous "monkey trial" in Dayton, Tennessee in 1925. Two renowned men, William Jennings Bryan for the prosecution and Clarence Darrow for the defense, debated the issues of "evolution" versus "creation." John T. Scopes, a schoolteacher, had been indicted and was being tried for teaching evolution to high school students. Scopes was in defiance of a Tennessee law that prohibited teaching any doctrines contrary to the Bible. This 20th Century Tennessee law was a direct descendant of the 13th century concept that any idea that contradicted the Bible was wrong.

Scopes was convicted and fined $100, but the conviction was later overturned on a legal technicality. It is interesting that today, 75 years after the famous trial, some conservative religious groups are still arguing against the Darwin-Wallace theory in virtually the same terms as in 1925! But perhaps the old Bible-versus-Science antagonism has been muted. In 1997, the Roman Catholic church decreed there is no essential conflict between the Biblical version of Genesis and the theory of evolution.

The Model's Social Impact: "Social Darwinism"

In the late 19th and early 20th Centuries, the theories of evolution and natural selection became both controversial and popular in the western world. Everyone, it seemed, had heard or read about the new ideas. This high visibility of scientific ideas among general populations was largely created by two factors. First, as already noted, there had been an intense, public, and highly inflammatory negative reaction from religious leaders. The vehement attacks actually brought attention to evolutionary theory, thus helping to propagate the ideas and insure that virtually everyone knew about them.

The second factor is the late 19th and early 20th Century growth in popularity of Social Darwinism. The concepts of evolution, struggle for existence, natural selection and survival of the fittest were the cornerstones of this increasingly popular view of history, society, and of the human condition in general. This was not a movement intended or aided by either Darwin or Wallace. However, given the growth of capitalism and industrialization and the extraordinary deep and massive social changes of the 19th Century, the model was eagerly accepted as a very useful and convenient rationale for the existence of human behaviors and conditions, such as unrestrained capitalism, epidemics, war, and poverty. Adherents maintained these were natural events in human and social evolution, and each had its proper role in the advancement of humans.

By the late 19th Century and beginning of the 20th Century, philosophers, sociologists, popular writers, and some very influential businessmen had become fervent Social Darwinists. As we noted earlier, this application of evolutionary concepts to human society had begun long before Darwin and Wallace and rose to its greatest popularity in the early 20th Century.

It is difficult to sort out the religious response to the model from the later applications to social issues, because the later Social Darwinists retained a moralistic, biblical fervor, and in many ways religion and sociology merged. One difference is that the religious reaction has been one of outright rejection, whereas the Social Darwinists embraced the model and many even maintained that it actually supported the notions of God's supremacy.

The most important of the Social Darwinists was Herbert Spencer (1820-1903), who predated the Darwin-Wallace model in his advocacy of an evolutionary view of human society. In the furor of criticism that followed publication of the Darwin-Wallace model, Spencer was one of a few notables who vigorously defended the new model. In Spencer's view, it gave scientific credence to his own social philosophy. For the public it seemed to scientifically confirm Spencer's position, boosting it to considerable eminence, especially in the United States. 

Spencer had been heavily influenced by the evolutionary models of the geologist Charles Lyell (1797-1875), the biologist Jean de Lamarck (1744-1829), and by Malthus' (1766-1834) conceptions about populations' responses to reduced resources (see above). Spencer was never a research scientist, did not contribute new data to the literature, and had little influence on science in general. His importance lies in integrating masses of scientific facts and concepts from several disciplines and his popularizing of the social evolution model in his many books. It was Spencer who, in 1852, coined the phrase "survival of the fittest" and used it to refer to human evolution. Later Darwin adopted the phrase.

Spencer's evolutionary-sociological model held that all forms of nature, including humans and their societies, naturally advance through evolution in a specific direction: from simpler, less complex, more homogeneous states to an increasingly differentiated, more complex, heterogeneous state. The direction of evolution is toward differentiation and complexity, where the many heterogeneous parts will finally evolve into perfect adjustment and equilibrium. Evolution moves toward some ideal of perfection. Thus, more recently evolved humans are "superior" to their evolutionary predecessors. In this evolution, there is struggle among individuals for limited resources. These natural conflicts include war and economic competition. 

Despite the suffering caused by such conflict, it is this struggle that brings about the survival of the fittest; it is this struggle that has led "men of feeble types" to their higher ethical and biological development. Individuals and collections of individuals (i.e., countries), who muster their abilities and succeed in the struggles, will predominate. They will have moved further along the evolutionary progression and, in accordance with Lamarckian principles of the inheritance of acquired characteristics, will pass on their superior qualities to their own children. Those who fail in this struggle will die out. Wars, for example, have been historically necessary in the development of higher types of humans by weeding out the unfit. According to Spencer, man has evolved beyond war, into the industrial state and war is no longer necessary; it has served its purpose.

For Spencer, the industrial state is a peaceful condition of cooperation, protection, and security among men of a higher (i.e., more evolved) ethical and physical order. (He could say this despite his assertion that it is competition and struggle that drive the modern industrial state.) Given the natural evolutionary direction of cumulative improvement, Spencer concluded that there must be no attempts to interfere with these natural processes (The man versus the state, 1884). Indeed, man cannot control his social environment and must simply leave it alone. Artificial social constructions, such as public charity, free education, poor laws, public health systems, labor unions, and any attempts to control industry or to shape society, are all antithetical to the evolutionary process and can only slow man's advancement. It is best to let the failures fail, to let them suffer from their own lack of ethics or competence. 

In his book Social Statistics (a laissez-faire theory, 1850), Spencer wrote that poor people, because they were not fit to survive, should in the proper course of events be eliminated. Also, persons with mental, physical, or moral defects will, in time, properly become extinct. Spencer wrote "If they are not sufficiently complete to live they die, and it is best they should die." Obviously, a society must not try to help such people survive. Let the evolutionary process proceed. Leave society alone and "survival of the fittest" will ensure man's continuing advancement. This is a markedly laissez-faire philosophy of strong individualism.

It is no surprise that Social Darwinism was so eagerly accepted by the 19th Century industrialists. Andrew Carnegie and John D. Rockefeller were in agreement that, while competition causes grief to many individuals, it is valuable for the whole race by insuring survival of the fittest. The growth of large business is merely a good example of survival the fittest; millionaires are obviously superior men who have succeeded over inferior types in their struggles. As a final example, we note sociologist William Graham Sumner's (1840-1910) comment, "If we do not like the (notion of) survival of the fittest we have only one alternative, and that is the survival of the unfittest!"

Social Darwinism preached evolution--slow, gradual, steady improvement--not revolution. Society in time will cure itself of all ills. Leave it alone. No concerted or central action must be taken to try and shape its course. Here was a strident individualism, a laissez-faire and even militaristic philosophy of the virtues of human competition toward racial (species) improvement. The times were right for its development and for the eager acceptance in the United States' 19th Century industrial society.

But by the end of the century its critics were growing in strength and included such notables as Thomas Huxley, Lester Ward, and David Jordan. Darwin-Wallace, they maintained, had been distorted and misapplied. The concepts of evolution and natural selection were used by these critics to support a very different social model--one of humanitarianism and cooperation, state action for the common good, and so on. 

Social Darwinism soon lost its pre-eminence in the United States. However, many of the ideas were taken up internationally in the early 20th Century's surge of nationalism, imperialism, and militarism. Strident assertions of "national destiny," and racial superiority by groups who considered themselves more highly evolved helped to drive the world into World War II. In a sense, the involvement of the United States in that huge war was our battle against the remnants of those highly distorted misapplications of the Darwin-Wallace model.

The impact on Psychology: Phylogenetic Continuity and Intra-species Variability

It is striking how profound ideas can be stated so simply and yet have such magnified effects on subsequent scientific thinking. This is the case with the Darwin-Wallace model, whose impact on science has been enormous. Its major scientific impact has been on the fields of biology, psychology, anthropology, and sociology. It stimulated a renewed interest in discovering and understanding fossils and other research in paleontology. It stirred new interest in the development of a science of genetics and helped to bring Mendel's little-known work of the 1860s (applying mathematics to understand genetic inheritance) to new prominence by the end of the century. Biology, neurology, and neuroscience are all indebted to the model. It has had powerful heuristic influence, stimulating new ideas even in its critics. 

For example, natural selection through minute variations did not seem plausible to the botanist Hugo De Vries (1848-1935), who was one of the first scientists to recognize and publicize the importance of Mendel's work. Such minor changes as observed by Darwin-Wallace, he thought, were controlled by recessive genes and could not result in creation of new species. De Vries created the idea of mutations--sudden, large, chance alterations in genetic material that bred true in the next generation. He experimented with plants and over many years successfully produced new plant forms. His discovery of the phenomenon of evolution through mutation modified the Darwin-Wallace model and has become a major concept in modern genetics.

The impact on Psychology stems primarily from two ideas: the continuity of form and function among animals and humans (phylogenetic continuity) and the fact of intra-species variability.

The first concept, phylogenetic continuity, was in direct conflict with the view of man's special creation--a philosophy of the discontinuity of man and animals. The two groups, it had been believed, are qualitatively different. With the advent of Darwin-Wallace it was suggested that men and animals share common ancestry and thus may be far more similar than different. This idea stimulated more animal research and allowed generalizations to be made about humans. Early work on the structure and function of animal nervous systems is an example.

Further, the idea of a biological or physical continuity makes possible the suggestion that there might also be a psychological continuity. Darwin (Expression of the emotions in man and in animals, 1872) argued that human emotions involve the inheritance of behavior developed in lower animals. He launched not only the psychological study of human emotions, but also the study of animal behavior (Boring, 1950).

Other researchers (e.g., George Romanes, 1848-1894) took up the study of animal behavior. A long line of animal research ensued; it was picked up by early American psychologists such as Thorndike and Watson. This early animal research was fundamental for much of American psychology through the mid-20th Century, with particular impact on the psychology of learning, behaviorism, and later, the development of behavior modification and behavior therapy in clinical psychology.

Edwin Boring (1950), the preeminent historian of experimental psychology, discussed how Darwin's interest in the inheritance of mental abilities substantially influenced early 20th Century psychology. Darwin's interest stimulated Francis Galton to his own far-reaching research on mental abilities, their distribution in the population, and the inheritance of mental capacities. Galton and others were to develop the central notion of "studying individual differences in mental capacities and of psychological assessment by means of mental tests" (Boring, pg. 472). 

It is no stretch to assert that the psychological testing movement was stimulated largely by Darwin-Wallace. In this movement, the notion of naturally-occurring intra-species variability, as observed by Darwin and Wallace, is a central concept not only in clinical and educational testing, but in all of psychological research. Individual variability is a fact of life. It is variability that allows us to draw population inferences from experiments and to develop normative bases for comparing individuals with one another.

As a final point, we note Boring's assertion that American psychology took a very different form--functionalism--from European psychology. Much of American functional psychology in the first half of the twentieth century focused upon the "assessment of personal capacities in the successful adjustment of the individual to his environment" (Boring, 1950, p. 507). Boring's thesis states that, because the United States so avidly took to ideas of evolution, intra-species variability, and natural selection, it was inevitable that Americans developed "a psychology of adaptation and survival value" (Boring, pg. 507).