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Jean-Baptiste Lamarck regarded geology and the study of living bodies as connected parts of a terrestrial natural philosophy. His Hydrogéologie by Jean-Baptiste Lamarck and Zoological Philosophy by Jean-Baptiste Lamarck sought lawful explanations of the Earth's changing surface and of changing organic organization. The connection was stronger than the commonplace that organisms live on land and in water: fluids and material transformations were supposed to make both the surface of the globe and living structures intelligible over immense periods.

One important starting point was the replacement of an explanation by exceptional events with a sustained investigation of ordinary causes and their accumulated consequences. Moving water could erode, transport and redeposit material. Over a sufficiently long interval, relatively small actions could change the relation between sea and land. This supplied a way of understanding a surface whose present arrangement need not be its original one. The explanatory appeal was to continuing physical operations plus duration, not to a modern theory of moving lithospheric plates. Calling his programme a fully formed modern uniformitarianism would obscure its distinctive mechanisms and assumptions.^[ref]

A related model operated within the organism. Jean-Baptiste Lamarck distinguished containing tissues from contained fluids, with moving fluids altering the structures through which they passed. More sustained or differently directed activity could strengthen or develop a part, while changing circumstances altered an animal's habits and the employment of its organs. The visible result was to be explained through a material history, rather than through a separate intention directly constructing each useful feature. This is why reducing his whole programme to the slogan that an animal wished for a new organ is misleading. Need, behaviour, fluid movement and organization occupied different places in the proposed causal sequence.^[ref]

There were also chemical connections between living and nonliving nature. In the 1809 work he argued that organisms formed their own compound substances and that their remains supplied materials subsequently transformed and simplified outside life. He expressly connected this discussion with Hydrogéologie by Jean-Baptiste Lamarck. Geology was consequently not a wholly independent history of an inert stage on which organisms later appeared. Organisms helped produce the materials of that stage; those materials, their environment and their transformations in turn conditioned living activity.^[ref]

The unity of explanation must nevertheless be stated carefully. Sharing physical and chemical causes did not mean that a crystal and an animal were indistinguishable. His comparison of inorganic and living bodies emphasized the organized, heterogeneous, bounded individual, with internal nutrition, development and eventual death. An inorganic aggregate did not acquire those capacities merely by becoming large. The special arrangement and circulation of matter therefore mattered to the explanation of life even when the causes acting on that arrangement were natural. There is no contradiction in claiming lawful material causes while also identifying organizational differences which require explanation.^[ref]

Nor should his chemistry be silently translated into modern biochemistry. His fluid and heat-based explanations, his conjectures about the formation and subsequent simplification of materials, and his accounts of the origin of simple living forms belonged to a particular early nineteenth-century system. To show why they fitted together is not to show that each is now accepted. Modern observations that organisms alter soils and sediments support some broad connections between life and the Earth's surface, but they do not establish his claim that all compound inorganic materials ultimately derived from living activity.

Finally, the integration helps explain his account of changing species. If environments have histories, their inhabitants encounter changing conditions. If habits and organization can respond, and acquired changes can persist through heredity, stable-looking forms need not be permanently fixed. His additional tendency toward more complex organization and the modifying effects of circumstances were not identical processes. The natural unity he sought was a framework for explaining both continuity of causes and diversity of outcomes. It was neither Darwinian natural selection avant la lettre nor a merely metaphorical comparison between rocks and animals. The conviction followed from a connected programme of material causation, long time and the historical production of structure.

Charles Darwin was neither the first nor the only pre-1859 advocate of changing species. The claim needs a second qualification: believing that species have histories is not the same as identifying natural selection, and neither entails that every lineage changes continuously at a constant rate. Several rival explanations were available before the publication of On the Origin of Species by Charles Darwin.

Jean-Baptiste Lamarck's 1809 programme is an unambiguous earlier example. In Zoological Philosophy by Jean-Baptiste Lamarck, forms which appear stable over a short interval can change through the accumulated effects of circumstances, altered habits, use and disuse, and transmission of acquired modifications. His separate account of increasing organizational complexity also mattered. This was a substantial causal programme, rather than a passing acknowledgment that individuals differ. It was not, however, an anticipation of every feature of Charles Darwin's explanation: an internally ordered tendency toward complexity and a response produced through an organism's activities differ from the sorting of heritable differences through unequal reproductive success.^[ref]

Robert Chambers's anonymously published Vestiges of the Natural History of Creation by Robert Chambers supplied another public alternative in 1844. It placed the succession of living forms within a law-governed history extending from the formation of the heavens to human beings. Its treatment of development was speculative and did not contain the developed selection mechanism of On the Origin of Species by Charles Darwin. Nevertheless, its very existence rules out an intellectual landscape in which an isolated Charles Darwin first introduced the possibility of organic change to an otherwise uniformly fixist audience. The difference between a privately developed theory and a book circulating publicly is especially important here.^[ref]

Alfred Russel Wallace provides the decisive counterexample even to the narrower claim of unique possession of natural selection. His 1858 essay argued that varieties could persist and depart progressively from their original type through differences in their capacity to survive under particular conditions. The materials jointly communicated to the Linnean Society on 1 July 1858 included his essay, extracts from Charles Darwin's earlier work and an account of his thinking in correspondence. The introductory communication explicitly presented the two as independent originators. This public event preceded the 1859 book and is stronger evidence than an attempt to infer influence from a loose resemblance between two later texts.^[ref]

There were also resources and disagreements beyond professed transformists. Geology supplied evidence of a long history; palaeontology documented succession and extinction; geographical distribution raised questions about affinities between inhabitants of neighbouring regions. Yet a commitment to extinction did not logically entail common descent, and an appeal to slowly acting geological causes did not oblige an author to accept changing species. The historical question is which inferences particular investigators drew from shared evidence, not whether a predecessor can be recruited to a modern camp merely because one premise resembles a later one.

What distinguished the 1859 synthesis was the scale and integration of the argument. Variation, heredity, the multiplication of organisms and limited opportunities for reproduction made unequal success consequential across generations. Branching descent could then connect adaptation, classification, geographical distribution and the fossil record. The theory did not require a breeder intentionally choosing the direction of change. At the same time, the first edition discussed other possible causes of variation and acknowledged serious difficulties. It should not be retrospectively equipped with a later genetic account of heredity.^[ref]

The appropriate judgment separates novelty of a general possibility, novelty of a mechanism and persuasiveness of a synthesis. Earlier and contemporary transformists defeat the first claim of solitary originality; the 1858 communication defeats the strongest version of the second. Neither fact erases Charles Darwin's achievement in constructing a sustained case. Equally, the premise of constant change is too crude: stable conditions, unequal rates and lineages persisting with little visible modification are compatible with a history of descent. Historical priority is best assessed by identifying the actual claim and evidence, rather than allocating one indivisible discovery called evolution.

Originality lay chiefly in an explanatory mechanism and a sustained evidential synthesis, rather than in the first suggestion that living forms might change. Charles Darwin combined existing problems and resources in a new way, while Alfred Russel Wallace's independent work prevents the mechanism of natural selection from being assigned to a wholly solitary origin.

Jean-Baptiste Lamarck had already offered a connected account of the transformation of living forms. His explanation gave substantial roles to changed circumstances, altered habits, use and disuse, and the transmission of acquired modifications. This was a serious attempt to explain organic change, not simply the absurd proposition that an animal obtains anything it wishes for. Nevertheless, a process that transforms individuals through altered activity differs from differential persistence and reproduction among variants. Recognizing that difference allows comparison without pretending that every earlier idea of evolution was already natural selection.^[ref]

Charles Darwin also drew on practices that were not inventions of an isolated theorist. Breeders' artificial selection demonstrated that cumulative choice among inherited differences could alter domestic forms. Thomas Robert Malthus's population argument made unrestricted multiplication and limited subsistence a problem requiring explanation. Geology, the fossil record and the geographical distribution of organisms supplied historical and spatial patterns that a theory of species had to address. None of these ingredients alone entailed Charles Darwin's conclusion. A population check might eliminate individuals without producing cumulative adaptive change; breeding involved a human chooser whose intentions could not simply be projected into nature.^[ref]

The distinctive inference joined inherited differences to unequal success in leaving descendants. If some variants leave more surviving offspring under particular conditions, and some relevant differences recur in their descendants, the composition of a population can change over successive generations. Natural selection consequently requires neither an organism's foresight nor a breeder intentionally specifying its destination. Competition also has a wider meaning than physical combat: it includes dependence on other organisms and on conditions necessary for reproduction. In this way an apparently purposive fit between organism and environment could be given a historical explanation.^[ref]

Charles Darwin's larger contribution was to make that process part of a theory of branching common descent. Divergence, extinction, the affinities used in classification, the distribution of organisms on islands and continents, and similarities of structure could be treated as connected consequences of a history of descent with modification. The argument accumulated partially independent kinds of evidence. It did not rest on displaying one adaptation and declaring that the rest of organic history must follow. It also openly discussed difficulties, including complex organs, hybridism and imperfections in the fossil record.^[ref]

The case of Alfred Russel Wallace is decisive for judging intellectual priority. In the Introduction to the 1859 On the Origin of Species by Charles Darwin, Charles Darwin explicitly acknowledged the arrival of Alfred Russel Wallace's memoir and the publication of their materials together. Alfred Russel Wallace's essay on varieties departing from the original type argued that struggle could favour particular variants and permit continuing divergence. Its later reprint identifies the 1858 publication and distinguishes that essay from subsequent additions to the collected volume.^[ref][ref] Independent convergence shows both that the mechanism was a real intellectual achievement and that the surrounding problems and observations were not private possessions.

Finally, the historical theory must be distinguished from later genetics. Charles Darwin did not possess a Mendelian explanation of heredity, and the 1859 book allowed roles for use and disuse and other causes of variation. It is therefore inaccurate to identify its entire content with a modern opposition between strictly genetic natural selection and a wholly separate Lamarckian alternative.^[ref] The qualified judgment is that Charles Darwin produced an unusually powerful synthesis and a major new causal argument, independently paralleled by Alfred Russel Wallace. Dependence on predecessors limits a claim of creation from nothing; it does not reduce the theory to the repetition of those predecessors.