The eclipse of Darwinism

Blending Inheritance

Jean Louis Agassiz 1870

Jean-baptiste lamarck2

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Blind insects in Packard's Mammoth Cave and its Inhabitants 1872

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Weismann's Germ Plasm

Titanothere Osborn

The Eclipse of Darwinism refers to a period in the late 19th and early 20th centuries when Darwin's theory of natural selection was challenged by alternative evolutionary theories. This period is characterized by scientific debate over the mechanisms of evolution, with many scientists exploring alternatives to natural selection, such as Lamarckism, orthogenesis, and mutation theory. The eclipse is considered to have ended with the modern synthesis of the 1930s and 1940s, which integrated Darwinian selection with genetics, re-establishing natural selection as the primary mechanism of evolution.

Background

Charles Darwin's publication of On the Origin of Species in 1859 proposed natural selection as the mechanism of evolution, but the theory was not immediately accepted by all. While Darwin's ideas gained popularity, there were significant gaps in understanding, particularly regarding the source of variation and how traits were inherited. This lack of a genetic framework led some scientists to seek alternative explanations for evolution.

Alternative Theories

Lamarckism

Lamarckism is based on the idea that organisms can pass on traits acquired during their lifetime to their offspring. This theory, named after Jean-Baptiste Lamarck, was one of the main alternatives considered during the eclipse of Darwinism. Lamarckism was attractive to some because it offered a direct mechanism for adaptation and evolution.

Orthogenesis

Orthogenesis, or "straight-line evolution," proposed that evolution follows a predetermined path, driven by internal or external forces, rather than by natural selection. This theory suggested that organisms have an innate drive to evolve in a particular direction.

Mutation Theory

The mutation theory, proposed by Hugo de Vries based on his work with the evening primrose, suggested that evolution occurs through large, sudden mutations rather than gradual change. This theory gained traction because it could explain the rapid appearance of new species without the need for gradual adaptation.

Decline of Alternative Theories

The alternative theories began to decline as the field of genetics advanced. The rediscovery of Mendel's work on inheritance in the early 20th century provided a genetic basis for natural selection, which had been lacking in Darwin's original formulation. The development of population genetics and the work of scientists such as Ronald Fisher, J.B.S. Haldane, and Sewall Wright further integrated genetics with natural selection, leading to the modern synthesis.

Modern Synthesis

The modern synthesis of the 1930s and 1940s reconciled Darwinian evolution with Mendelian genetics, establishing a unified theory of evolution that emphasized natural selection as the primary mechanism. This synthesis also incorporated concepts from paleontology, systematics, and morphology, providing a comprehensive framework for understanding evolution.

Impact

The eclipse of Darwinism and the subsequent modern synthesis had a profound impact on the field of biology, solidifying the role of natural selection in evolutionary theory and integrating genetics into the study of evolution. This period also highlighted the importance of scientific debate and the self-correcting nature of scientific inquiry.

See Also

• History of evolutionary thought
• Modern evolutionary synthesis
• Genetics
• Natural selection