The Eclipse of Darwinism - Neo-Lamarckism

Neo-Lamarckism

Jean-Baptiste Lamarck had originally proposed a theory on the transmutation of species that was largely based on a progressive drive toward greater complexity. Lamarck also believed, as did many others at the time, that characteristics acquired during the course of an organism's life could be inherited by the next generation, and he saw this as a secondary evolutionary mechanism that produced adaptation to the environment. Typically, such characteristics included changes caused by the use or disuse of a particular organ. It was this mechanism of evolutionary adaptation through the inheritance of acquired characteristics that much later came to be known as Lamarckism. Although Alfred Russel Wallace completely rejected the concept in favor of natural selection, Charles Darwin always included what he called Effects of the increased Use and Disuse of Parts, as controlled by Natural Selection in On the Origin of Species, giving examples such as large ground feeding birds getting stronger legs through exercise, and weaker wings from not flying until, like the ostrich, they could not fly at all.

In the late 19th century the term neo-Lamarckism came to be associated with the position of naturalists who viewed the inheritance of acquired characteristics as the most important evolutionary mechanism. Advocates of this position included the British writer and Darwin critic Samuel Butler, the German biologist Ernst Haeckel, the American paleontologists Edward Drinker Cope and Alpheus Hyatt, and the American entomologist Alpheus Packard. They considered Lamarckism to be more progressive and thus philosophically superior to Darwin's idea of natural selection acting on random variation. Butler and Cope both believed that this allowed organisms to effectively drive their own evolution, since organisms that developed new behaviors would change the patterns of use of their organs and thus kick-start the evolutionary process. In addition, Cope and Haeckel both believed that evolution was a progressive process. The idea of linear progress was an important part of Haeckel's recapitulation theory of evolution, which held that the embryological development of an organism repeats its evolutionary history. Cope and Hyatt looked for, and thought they found, patterns of linear progression in the fossil record. Packard argued that the loss of vision in the blind cave insects he studied was best explained through a Lamarckian process of atrophy through disuse combined with inheritance of acquired characteristics. Packard also wrote a book about Lamarck and his writings.

Many American proponents of neo-Lamarckism were strongly influenced by Louis Agassiz and a number of them, including Hyatt and Packard, were his students. Agassiz had an idealistic view of nature, connected with natural theology, that emphasized the importance of order and pattern. Agassiz never accepted evolution; his followers did, but they continued his program of searching for orderly patterns in nature, which they considered to be consistent with divine providence, and preferred evolutionary mechanisms like neo-Lamarckism and orthogenesis that would be likely to produce them.

In Britain the botanist George Henslow, the son of John Stevens Henslow who had been Darwin's mentor at the University of Cambridge, was an important advocate of neo-Lamarckism. He studied how environmental stress affected the development of plants, and he wrote that the variations induced by such environmental factors could largely explain evolution. The science historian Peter J. Bowler writes that, as was typical of many 19th century Lamarckians, Henslow did not appear to understand the need to demonstrate that such environmentally induced variations would be inherited by descendants that developed in the absence of the environmental factors that produced them, but merely assumed that they would be.

Critics of neo-Lamarckism pointed out that no one had ever produced solid evidence for the inheritance of acquired characteristics. The experimental work of the German biologist August Weismann resulted in the germ plasm theory of inheritance. This led him to declare that inheritance of acquired characteristics was flatly impossible, since the Weismann barrier would prevent any changes that occurred to the body after birth from being inherited by the next generation. Despite these criticisms, neo-Lamarckism remained the most popular alternative to natural selection at the end of the 19th century, and would remain the position of some naturalists well into the 20th century.