: Darwinism

Overview

Alfred Russel Wallace's Darwinism (1889) gives a systematic, accessible defense and development of the theory of natural selection as the primary mechanism of organic evolution. Wallace treats natural selection not as a speculative hypothesis but as a powerful explanatory framework that unifies diverse biological facts, from morphology and embryology to geographical distribution and the fossil record. The tone is both polemical and pedagogical: Wallace aims to persuade skeptics while guiding educated readers through the chain of evidence that, he argues, makes Darwin's ideas the most satisfactory account of biological change.

Core arguments

Wallace emphasizes variation, heredity, and the struggle for existence as the engine that drives adaptation. He explains how small heritable differences, when subjected to differential survival and reproduction in a competitive environment, accumulate over generations to produce new species and complex structures. Special attention is given to "divergence of character, " the way populations branching into different environments evolve distinct adaptations, and to the cumulative action of selection in producing apparent design without invoking purpose or foreknowledge. Wallace underscores the economy of natural selection: it explains multiple phenomena with a single, coherent principle.

Evidence and illustrative cases

The book marshals a wide array of empirical material: comparative anatomy demonstrates homologies and gradations of structure; embryology reveals conserved developmental patterns; biogeography shows how isolation and environment shape lineages; and paleontology supplies sequences of change, however incomplete. Wallace draws on island faunas, mimicry in insects, the function and variation of organs, and the geographic distribution of closely related species to illustrate how selection operates in nature. These cases serve both to justify selection's explanatory reach and to show how alternative theories fare poorly when confronted with concrete data.

Responses to objections

Wallace systematically addresses common criticisms of selection, including the perceived absence of transitional forms, the difficulty of explaining complex organs, and the role of use-inheritance. He argues that gaps in the fossil record are expected given geological and preservation biases and that gradual modification through intermediate stages explains complexity without recourse to supernatural or teleological forces. He disputes Lamarckian explanations and other non-selective mechanisms as either unnecessary or inadequate, while admitting that some supplementary causes, such as correlation of growth or sexual selection, can play modifying roles alongside natural selection.

Applications and implications

Beyond theory, Wallace explores the implications of Darwinism for classification, human origins, and practical biology. He treats the human species as part of the natural order, subject to the same evolutionary processes that shape other organisms, though he is cautious about overstating how much selection explains higher mental faculties. The book also considers the consequences of evolutionary thinking for how humans understand diversity, the unity of life, and the limits of teleological explanations in natural history.

Style and legacy

Written in clear, vigorous prose, Darwinism aims to be both an introduction and a comprehensive defense. Wallace's clarity and his ability to synthesize evidence made the book influential in consolidating acceptance of natural selection among late 19th-century readers. It stands as a notable statement by one of the co-discoverers of natural selection, highlighting both the strengths of Darwin's theory and the areas where further research was needed.