Invertebrate Zoology, Lamarckism, and Their Influences on the Sciences and on Society

views updated

Invertebrate Zoology, Lamarckism, and Their Influences on the Sciences and on Society

Overview

The ideas of naturalist and systematist Jean Baptiste de Lamarck (1744-1829) influenced the notions surrounding evolution and also sparked social Lamarckism, which developed years after his death. He was also responsible for making a respectable field out of the study of invertebrates. On the evolutionary front, Lamarck propounded evolution and the mutability of species, but is best known for his "use and disuse" hypothesis. This hypothesis states that traits acquired during an individual's life span can be passed from generation to generation. After his death, many writers and philosophers rallied behind and expanded upon Lamarck's equivocal belief that animals have control over their evolutionary course. The product was social Lamarckism, an unorganized but influential movement.

Background

Lamarck died some thirty years before the publication of Charles Darwin's theory of evolution by natural selection in 1859. While many of Lamarck's ideas were later found to be misguided, his belief in evolution and the mutability of species helped set the stage for their future scientific consideration.

His scientific career took a turn from botany, in which he had gained a solid reputation, when his employer, France's Jardin des Plantes, reorganized into the National Museum of Natural History (Muséum National d'Histoire Naturelle). Lamarck became the museum's professor of "insects and worms," a new field for this man who was nearing 50 years of age. In the years to come, he would coin the term invertebrates for this group of organisms and make great contributions in their classification.

While Lamarck was developing his considerable skills as an invertebrate systematist, he spent many hours considering the method of evolution and devised a "use and disuse" hypothesis. He suggested that organisms over their lifetime could incur alterations to their organs and structures simply by using them more or using them less. For example, a bird might develop stronger lungs to account for the heightened energy demands of flight, whereas a burrowing mole's eyes might degenerate and become smaller, because the animal had no need for them. Any changes acquired during the animal's lifetime would pass down to its descendants. Over time, the animal would evolve to enhance these altered traits.

Lamarck also considered whether animals could "will" these changes, occasionally propounding that they did indeed have control over their evolutionary paths. His thoughts on this idea shifted, but they nonetheless spurred considerable debate, particularly in the century following his death.

Impact

Lamarck's work in systematics became a foundation for future invertebrate classification. Before he took on this formidable task, the invertebrates were considered lower life forms that required and deserved little attention, compared to other animals and to plants. When he accepted his position at the National Museum of Natural History, he quickly became intrigued by these neglected animals and recognized that the group contained an enormous diversity too large to be lumped into one classification. He divided the invertebrates into such groups as the arachnids (spiders and their allies) and annelids (earthworms and their allies)—classifications that persevere today. In many scientists' eyes, he is the father of invertebrate zoology.

Lamarck also received acclaim as a naturalist for his earlier botanical work, particularly by way of his well-received 1778 publication Flore Française, which described the plants of France.

It was Lamarck's ideas on evolution, however, that would bring the most notice to the French naturalist. At the turn of the century, Lamarck began to speculate about the method of evolution, and in 1809 outlined them in Philosophie Zoologique. While other evolutionists were suggesting that the environment directed the varied alterations in an organism, Lamarck felt that environmental modification triggered an organism's "need" or "urge" to change. The organism responded to that need by developing behaviors that led to increased or decreased use of various organs or structures. If no corresponding organs existed, the organism would generate one. This "First Law," as described by Lamarck, allowed that organs and structures could enlarge or shrink based on their use. His "Second Law" stated that these acquired traits could be passed on to descendants. In other words, organisms changed gradually over time because their needs ultimately drove their responses to environmental changes and those acquired responses were heritable. Over the years, Lamarck also espoused that organisms have control over the "needs" and "urges," and could thus direct their evolution.

Lamarck's ideas remained largely unknown during his life, because general opinion held that evolution was simply incorrect, and species instead existed unchanged over time. In the mid-to late-1800s, however, the scientific side of Lamarck's "use and disuse" hypothesis began to generate considerable discussion and argument. That changed when the study of genetics began in earnest in the early 1900s as Gregor Mendel's experiments on heritability were rediscovered. Eventually scientists confirmed that genes transfer traits from generation to generation, and that acquired traits were not heritable. The "use and disuse" hypothesis was torn asunder. Additional blows to Lamarck's ideas accumulated as scientists began to understand that evolution was driven by random, nondirected mutations. Evolution had no defined, progressive path as Lamarck suggested.

Lamarck's ideas gained a brief resurgence around the time of World War I when Austrian biologist Paul Kammerer (1880-1926) reported experimental results that seemed to support the idea of heritable acquired traits. His experiments centered around a species of toad that lived on dry land. While the males of most toad species living in moist habitats have a pad on their fore-limbs to assist in gripping the female during mating, this dry-land species no longer carried the trait. Kammerer reared the toad in an artificially moist habitat, and reported that the toad developed the formerly absent pads. He also reported that the pads were heritable.

After worldwide publicity about his findings, including media speculation that the experiments opened the door to the creation of modified and enhanced human beings, skeptical scientists examined a preserved specimen of the padded males to find that the dark pads were a result of an application of India ink. Kammerer claimed that the ink was merely an attempt by a student to retain the pad's coloration, which had faded during preservation. With his credibility in ruins, Kammerer killed himself.

Despite the decline in the scientific value of Lamarck's ideas, his hypotheses generated a significant impact in the social arena. In the late nineteenth century and early twentieth century in particular, many philosophers began to select portions of Lamarck's ideas, augment them, and create what came to be called Lamarckism. In particular, they singled out his beliefs that a species may have some control over its future state and that evolution encompasses a trend toward perfection.

In Philosophie Zoologique, Lamarck submitted that evolution is a progressive path with lower, imperfect forms at the bottom of the evolutionary tree and higher, more perfect forms at the top. Man was the most complex and perfect. Evolution, then, was a means toward perfection. Because all organisms would over time progress to the top of the tree, he reported that nature must continuously add new organisms to the bottom of the tree via spontaneous generation.

As with a number of his other ideas, Lamarck remained flexible in his opinions. He alternated between convictions that organisms could or could not control their evolutionary destiny, and that evolution was progressive versus solely a response to local environmental conditions. His lack of scientific evidence to back up or refute any of his claims gave him considerable reign to explore philosophical questions and put forth various hypotheses. Contemporary and later critics of Lamarck noted this lack of scientific credibility as a major fault. Darwin was one of Lamarck's greatest critics, and often made a point of distancing his ideas from those of Lamarck. Other scientists, however, looked back on Lamarck as an important thinker of his time.

Supporters of Lamarckism ignored the naturalist's misgivings about some of his own ideas, along with the absence of a scientific basis for them, and developed a rather unorganized social movement that embraced the idea that organisms, including humans as the highest form, could continue to direct the betterment of themselves in succeeding generations. Lamarckians did not accept that evolution was driven by random, nondirected mutations. Lamarckism was a philosophy filled with optimism, but not for all human races. Lamarckians believed that among humans, white races ranked at the top of the evolutionary tree, and non-white races fell somewhere below. Lamarckians felt that humans could progress most effectively through cooperative social reform and grand educational programs. They believed that learned behavior would be passed along to subsequent generations, a notion which had been refuted by biologists and scientists.

British social philosopher Herbert Spencer (1820-1903), who is often mentioned in connection with Lamarckism, actually limited his connection to this movement by taking up its use-inheritance pretense as the foundation of evolution, but maintaining that nature instead of nurture guided evolution. Spencer is more aptly described as a social Darwinist, who helped promote the "survival of the fittest," a phrase he coined. He held that the individuals who were most well adapted were also most likely to survive and reproduce. Like Lamarckism, social Darwinism fell from popularity in the early 1900s.

LESLIE A. MERTZ

Further Reading

Bowler, Peter J. Evolution: The History of an Idea. Rev. ed. Berkeley: University of California Press, 1989.

Bruno, Leonard C. The Tradition of Science: Landmarks ofWestern Science in the Collections of the Library of Congress. Washington, DC: Library of Congress, 1987.

Byers, Paula K. Encyclopedia of World Biography. 2nd ed. Detroit: Gale Research, 1998.

Greene, John C. The Death of Adam: Evolution and ItsImpact on Western Thought Ames, IA: Iowa State University Press, 1959.

Lamarck, J. Philosophie Zoologique. New York: Lubrecht and Cramer, 1960.

Lamarck, J. Zoological Philosophy: An Exposition withRegard to the Natural History of Animals. New York: AMS Press, 1963.

Singer, Charles. A Short History of Scientific Ideas to 1900. London: Oxford Press, 1959.

About this article

Invertebrate Zoology, Lamarckism, and Their Influences on the Sciences and on Society

Updated About encyclopedia.com content Print Article Share Article