Population Theory: Malthus's Influence on the Scope of Evolution

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Population Theory: Malthus's Influence on the Scope of Evolution


Approximately 60 years before the now historic publication of Charles Darwin's On the Origin of Species in 1859, Reverend Thomas Robert Malthus (1766-1834) penned a commentary on what he perceived to be the destiny of the human population in eighteenth-century Britain. Malthus's Essay on the Principles of Population profoundly impacted the evolutionary theories of Charles Darwin (1809-1882) and Alfred Russel Wallace (1823-1913), and continues to resonate through social, political, and environmental issues that affect the lives of people today.


Prior to 1750, agricultural practices were as they had been since the Middle Ages. Great Britain was an agricultural society in which farmers worked long hours using simple tools—wooden plows, hoes, and scythes—to produce scanty crops. Using these tools and techniques, farmers were scarcely able to eke out a living. The mid-1700s saw a shift from an agricultural society to an industrial society as new farming practices and mechanization, the growing use of machines, reduced the number of workers needed to produce food for Europe's growing population. As a result, unemployed farmers migrated to the new industrial towns to seek employment in factories.

The Industrial Revolution radically transformed the economic structure of British society from a system of feudalism—a hierarchical system of lords and serfs that concentrated wealth at the top—to one of capitalism. Free enterprise and cost efficient machines caused factory owners, bankers, and entrepreneurs to gain significant wealth and power. The middle and upper classes prospered from the labors of the poor who filled the factories and toiled long hours for little pay.

Malthus's Essay on the Principles of Population was written in response to William Godwin's The Enquirer. In The Enquirer Godwin (1756-1836) promoted population growth as the stimulus for attaining equality among men. Godwin described population growth as a positive force that paves the way to greater wealth and improvement for all. Malthus attempted to point out weaknesses in Godwin's philosophy by way of simple mathematics. Rather than seeing increasing population size as a way of improving the standard of living for all Britons, Malthus viewed it as a limiting factor that reduced the opportunity for the poor to escape from the miseries and hardships of their daily lives.

Malthusian principle states that populations grow geometrically while resources grow only arithmetically. Simply stated: Population grows much more quickly than the food supply. Malthus believed that the inability of available resources to keep pace with ever increasing population size ultimately results in a continuing struggle for survival by the lower economic classes. His Essay on the Principles of Population describes the outcome of mankind's struggle to obtain increasingly limited resources as a life filled with misery and vice. It was this concept of a struggle for survival within large populations that was adopted by evolutionary biologists, forever changing evolutionary thought.


The impact of Malthus's Essay on the Principles of Population on Charles Darwin as he sought the mechanism for evolution has never been understated. Darwin himself recorded in his 1876 autobiography the following:

"In October 1838, that is, fifteen months after I had begun my systematic inquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The results of this would be the formation of a new species. Here, then I had at last got a theory by which to work."

Malthus's work caused Darwin to refocus on a bigger picture. While Darwin's predecessor, Jean Baptiste de Lamarck (1744-1829), and contemporaries such as Jean Agassiz (1807-1873) and Richard Owen (1804-1892) focused on individual organisms and the belief that something was driving the evolution of organisms in a direction toward perfection independent of environmental influence, Darwin dismissed this popular theory and continued his quest for another explanation.

Upon reading Essay on the Principles of Population, both Darwin and Alfred Russel Wallace independently adapted Malthus's "struggle for existence" principle and applied it to plant and animal species, thereby arriving at the theory of natural selection. Darwin's theory of natural selection stretches Malthus's principle beyond the boundaries of the human population and political economy. Darwinian theory of natural selection made the connection between organisms and their environments stronger than they had ever been.

Prior to Darwinian theory, many believed that individual plants and animals changed in response to their environments. According to Lamarkian theory, then the dominant school of thought with regard to evolution, a giraffe's neck grows longer in its lifetime to reach leaves on taller trees. This individual, in turn, passes this acquired trait on to its offspring. Thus, it was believed, organisms change in response to their environment. However, under this model it would seem that the environment exerts little direct pressure on a species.

Darwin's model challenged the passive role of the environment. He proposed that the environment set the stage for a competition for survival. In economics, as in biology, those that are best able to compete are best able to survive. In a capitalist society, those that are most successful, as measured by accrued wealth, are those who are able to best utilize their resources. Similarly, environment or factors within the environment select for those traits that enable plants and animals to survive long enough to reproduce.

Darwin recognized that many plant and animal species produced far more offspring than could survive. Upon reading Malthus, he surmised that the large numbers of offspring are produced in a biological gamble. According to the selection theory, within the large numbers of offspring some will have the traits that will aid in their survival and will pass desirable traits on to their offspring. Those lacking the traits needed to successfully utilize resources and reproduce do not survive.

The idea that organisms and species survive as a result of characteristics selected for by the environment did not sit well with orthodox religion. The automated nature of the selection process precludes the involvement of a divine figure. Additionally, Christian philosophy holds all life as a gift. In light of Darwinian theory, the essential randomness and apparent wastefulness of the selection process argued against any form of divine intervention. This significant difference in philosophy resulted in battle lines being drawn between Creationists—those believing that the hand of God guides changes in species—and Evolutionists—those contending that species change as a function of natural selection.

Malthus's influence is still felt today as the battle rages on between Creationists and Evolutionists, affecting the way Evolution is taught in schools across America. Similarly, as global population approaches six billion, concerns continue to mount over the Earth's ability to support the growing human population, while at the same time preserving essential ecosystems and maintaining biological diversity.


Further Reading

Fedoroff, Nina V., and Joel E. Cohen. "Plants and Populations: Is there time?" Proceedings of the National Academy of Science 96 (25 May 1999): 5903-5907.

Ghiselin, Michael T. "Perspective: Darwin, Progress, and Economic Principles." Evolution 49 (December 1995): 1029-1037.

Thomson, Keith Stuart. "1798: Darwin and Malthus." American Scientist 86 (May-June 1998): 226-229.

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