Table of Contents
In the “History of Evolutionary Thought,” early scientific approaches to descent form an important bridge between mythological or purely philosophical ideas and the later, systematically developed evolutionary theories of the 18th and 19th centuries. Here, naturalists began to treat the origin and diversity of organisms as empirical questions that could, at least in principle, be answered by observation and reasoning about nature itself.
This chapter focuses on these first, still incomplete, but scientifically motivated attempts to explain how organisms might be related by descent and how new forms could arise over time.
From Static Species to Historical Thinking
In earlier creationist views, species were usually regarded as:
- Timeless (without real beginning or end in time)
- Unchanging (no transformation from one species into another)
- Perfectly fitted to their environment by an act of creation
Early scientific approaches to descent did not yet abandon the idea of creation altogether, but they began to introduce time and history into the understanding of living beings. Key shifts included:
- The idea that species may have appeared at different times rather than all at once.
- The suggestion that species might go extinct and not be recreated, implying an irreversible historical process.
- First doubts that all species are strictly unchangeable.
These shifts emerged mainly from three sources: the study of fossils, early classification systems, and comparative anatomy.
Fossils and the Question of Extinction
As naturalists in the 17th and 18th centuries collected fossils, they were confronted with remains of organisms that no longer seemed to exist in the living world.
From “Games of Nature” to Remains of Past Life
Initially, some scholars regarded fossils as:
- “Lusus naturae” (games or sports of nature), mineral curiosities formed inside rocks, not remains of real organisms.
- Traces of the biblical Flood that had scattered living forms—as in some interpretations, fossils could be shells and bones of creatures still living elsewhere.
However, more systematic study led to a different conclusion:
- The detailed similarity between certain fossils and living organisms (e.g., ammonites and modern cephalopods) showed that fossils had once been living beings.
- The absence of exact living counterparts suggested that some forms had disappeared.
The idea of extinction was revolutionary because:
- It contradicted the notion that creation was perfect and complete—why would a creator allow forms to vanish?
- It implied a historical sequence of faunas and floras, different at different times.
Although many early naturalists still believed in multiple creations or catastrophic events that wiped out and replaced faunas, the recognition of extinction created space for later notions of succession and transformation of species.
Early Systematics and the Fixity of Species
The development of systematics—the science of classifying organisms—was essential for later evolutionary thinking, even though most early systematists did not themselves accept species change.
Carl Linnaeus (1707–1778)
Linnaeus (or Linné) was a central figure in this development. His contribution to early scientific approaches to descent is paradoxical:
- On the one hand, he was a strong proponent of the fixity of species:
- Species, in his view, were created as distinct, immutable units.
- He often wrote of species as “as many as the Infinite Being created in the beginning, so many there are and will be.”
- On the other hand, his work laid crucial groundwork for later descent theories by:
- Introducing a hierarchical classification (species, genus, family, order, class, etc.).
- Grouping organisms according to shared characteristics, rather than utility or folklore.
This hierarchical system forced naturalists to ask:
- Why do some organisms resemble each other so closely that they belong to the same genus?
- Why do higher groups (families, orders) cluster many genera with similar features?
Although Linnaeus explained such patterns as reflections of a rational plan of creation, the structure of his system itself suggested natural relationships that later scientists would interpret as relationships of descent.
First Hints of Variability
Over time, Linnaeus became aware that:
- Plants can hybridize and produce fertile offspring that differ from both parents.
- Slight differences between populations (e.g., in color, size) could be stable in nature.
These observations led him to cautiously admit that:
- What he called “varieties” could arise within a created species.
- In rare cases, he considered that a new “species” might result from hybridization.
Although he did not develop an explicit theory of evolution, these concessions weakened the strict boundary between an absolutely fixed species and observed variation, and inspired later thinkers to extend variation over longer time scales.
Comparative Anatomy and the “Unity of Type”
While systematists like Linnaeus worked on external features and classification, comparative anatomists studied internal structures and discovered deeper similarities across apparently different animals.
Homologous Structures and Archetypes
Early anatomists noticed that:
- The limb skeleton of a bat, a horse, a whale, and a human share the same basic pattern: one upper bone, two lower bones, wrist/ankle bones, and a series of digits.
- Vertebrate skulls, vertebral columns, and other internal structures also show repeated patterns.
These structural correspondences suggested a “unity of type”—a common basic plan shared by many organisms.
In a non-evolutionary framework, this unity of type was usually explained as:
- Evidence of a single, rational design employed by the creator.
- A realization of an ideal “archetype” in multiple variations.
But the very existence of such systematic similarities made it easier, later on, to reinterpret them as signs of common ancestry and descent with modification.
Functional vs. Structural Explanations
At the same time, naturalists distinguished between:
- Adaptation to function (e.g., wings adapted for flight, fins for swimming).
- Underlying structural plan (the shared skeletal layout, regardless of particular function).
This separation made it possible to ask:
- If the same structure can serve different functions in different species, might those species have diverged from a common starting point?
Early scientific approaches did not yet answer this question in evolutionary terms, but they posed it clearly.
Gradualism and the Chain of Being
While fossils and anatomy introduced historical and structural questions, another influential idea concerned the organization of all life.
The “Great Chain of Being” Becomes Naturalized
Earlier philosophical and religious traditions had imagined a “Great Chain of Being”:
- A continuous order from the simplest to the most complex, from inanimate matter to plants, animals, humans, and spiritual beings.
- Each “link” had its assigned place, and the chain was usually thought to be fixed.
In the early modern period, naturalists began to reinterpret this chain more naturalistically:
- Organisms were arranged from “lower” to “higher” based on observable complexity.
- Some authors speculated that nature might “graduate” from simple to complex forms in small steps.
Although many still denied that one species literally transformed into another, they:
- Emphasized continuity in the series of forms.
- Sometimes suggested that new species could be “inserted” into gaps in the chain by natural processes.
This linear view of nature prepared the ground for thinking about gradual transformation, even if it still lacked a clear mechanism.
First Transformist Ideas Before Darwin
Well before a full-fledged evolutionary theory emerged, some naturalists put forward transformist ideas—proposals that species might actually change over time and give rise to new species.
Without going into the details of complete later theories, it is important in this chapter simply to note the nature of these early, often tentative approaches.
Environmental Influence and Degeneration
Some authors suggested that:
- Species could degenerate or change when they moved into new environments, such as different climates or diets.
- Human “races,” for example, were sometimes explained as varieties formed by environmental influences since an original creation.
These ideas applied the known effects of climate or lifestyle on individuals and populations to longer timescales, hinting—still cautiously—that such changes could accumulate.
Successive Creations and Temporal Ordering
Other naturalists, influenced by geology, proposed that:
- The Earth had passed through successive ages with distinct faunas and floras.
- After catastrophes (e.g., floods, upheavals), new species were created or appeared.
Even though this view retained multiple acts of creation, it recognized:
- A temporal ordering of organisms in the geological record.
- Increasing complexity or changing composition of faunas across strata.
Again, while not yet true “evolution,” it shifted attention from a single, static creation toward a history of life that unfolds in stages.
Limits and Significance of Early Scientific Approaches
Early scientific approaches to descent remained incomplete and often inconsistent:
- Many authors held on to creationist assumptions while describing patterns that suggested descent.
- Variation, extinction, and adaptation were recognized, but not yet integrated into a coherent mechanism for producing new species.
- Time scales were often still short compared to what we now know from geology and paleontology.
Nonetheless, these early approaches were crucial because they:
- Replaced mythological explanations with empirical investigation—of fossils, comparative anatomy, and geographic distribution.
- Developed a language and toolkit (classification, homology concepts, stratigraphy) that later evolutionary theories would rely on.
- Introduced historical thinking into biology, treating life as something that unfolds over time, not merely a static reflection of an eternal plan.
In subsequent chapters on pioneers of scientific evolutionary theory and Darwin’s theory, these elements—extinction, variation, unity of type, and the temporal sequence of life—will be assembled into more comprehensive and explicitly evolutionary explanations of descent.