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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.