In the Journal of the History of Biology:
Abstract Darwin’s first two, relatively complete, explicit articulations of his theorizing on evolution were his Essay of 1844 and On the Origin of Species published in 1859. A comparative analysis concludes that they espoused radically different theories despite exhibiting a continuity of strategy, much common structure and the same key idea. Both were theories of evolution by means of natural selection. In 1844, organic adaptation was confined to occasional intervals initiated and controlled by de-stabilization events. The modified descendants rebalanced the particular “plant and animal forms … unsettled by some alteration in their circumstances.” But by 1859, organic adaptation occurred continuously, potentially modifying the descendants of all organisms. Even natural selection, the persistent core of Darwin’s theorizing, does not prove to be a significant basis for theory similarity. Consequently, Darwin’s Origin theory cannot reasonably be considered as a mature version of the Essay. It is not a modification based on adjustments, further justifications and the integration of a Principle of Divergence. The Origin announced a new “scientific paradigm” while the Essay did little more than seemingly misconfigure the operation of a novel mechanism to extend varieties beyond their accepted bounds, and into the realm of possible new species. Two other collections of Darwin’s theorizing are briefly considered: his extensive notes of the late 1830s and his contributions to the famous meeting of 1 July 1858. For very different reasons, neither constitutes a challenge to the basis for this comparative study. It is concluded that, in addition to the much-debated social pressures, an unacknowledged further reason why Darwin did not publish his theorizing until 1859, could have been down to his perceptive technical judgement: wisely, he held back from rushing to publish demonstrably flawed theorizing.
In the Biological Journal of the Linnean Society:
Joachim L Dagg
Abstract A comparison of the evolutionary mechanisms of Patrick Matthew, Charles Darwin and Alfred Wallace highlights their differences. In Matthew’s scheme, catastrophes initiate periods of radiation and speciation until a fully stocked environment enters into stasis. Catastrophes first need to exterminate competing species before the survivors can radiate into free niches and diversify into new species. In Darwin’s early theory, conditions of life, such as those prevailing under domestication, first need to increase the variability of a species before natural selection can transform it. In Darwin’s mature theory, competition replaces conditions as the main drive behind evolutionary change, and sympatric speciation becomes possible. Wallace’s theory differs from both Matthew’s and Darwin’s. Interspecific competition is not a brake halting transmutation (as in Matthew’s theory) nor is intraspecific competition a sufficient drive for it. Although each theory integrated natural selection with variability, competition and changed conditions in distinct ways, each allowed for species transmutation somehow. The result was similar (transmutation), but the mechanisms yielding that result (the integration of natural selection with variability, competition and change in conditions) differed significantly.
Additional thoughts from the author of the above article here.
And in Historical Studies in the Natural Sciences, an essay review by Richard Bellon of the books Darwin and the Making of Sexual Selection by Evelleen Richards, Darwinism and Religion: What Literature Tells Us About Evolution by Michael Ruse, Masculinity and Science in Britain, 1830-1918 by Heather Ellis, and Orchids: A Cultural History by Jim Endersby.