Basic Premises of Evolutionism: Unilinear, Universal, and Comparative Approaches

Picture the world through nineteenth-century European eyes: steam engines were reshaping economies while indigenous societies elsewhere still lived by hunting and gathering. Instead of chalking this up to different histories and environments, early anthropologists proposed something far bigger: every society, without exception, was walking the same road toward “civilization.” This was the birth of classical evolutionism, and its basic premises still shape how we think about culture today, even as we’ve moved past its flaws. Let’s unpack the three big ideas that held this school of thought together.

The single line of progress: Unilinear evolutionism 🔗

The core claim of classical evolutionism was simple: all societies move from simple to complex along one fixed track, with no shortcuts and no detours. This is unilinear evolutionism. Scholars like Edward Tylor and Lewis Henry Morgan proposed that every society passes through the same broad stages, usually labelled savagery, barbarianism, and civilization, and that the sequence itself never changes, only the speed at which different groups move through it.

This wasn’t a minor observation buried in academic footnotes. It became the organizing principle of an entire discipline. The notion of dividing the ethnological record into evolutionary stages ranging from primitive to civilized sat at the heart of nineteenth-century social evolutionary theory. Notice what this implies: if a society looked “less developed” than Victorian England, that wasn’t because it had a different history or different priorities. It was because it hadn’t caught up yet.

No skipping stages allowed 🔗

A crucial detail here is the word “fixed.” Evolutionists weren’t just saying societies change over time, they were saying societies must move through every stage in order, with no possibility of jumping ahead or taking an alternate path. A tribal society and an industrial one weren’t seen as different kinds of social organization. They were seen as the same organization at different points on the same timeline. This rigid, staircase-like model is what set unilinear evolutionism apart from later, more flexible theories of change.

Universal evolutionism and the psychic unity of mankind 🔗

If every society follows the same path, evolutionists needed an explanation for why. Their answer was a concept called the psychic unity of mankind, originally formulated by the German scholar Adolf Bastian and later picked up enthusiastically by British evolutionists. The idea, in plain terms, is that all human beings share a similar mental makeup, and that similarities between cultures reflect similar underlying mental processes rather than contact or copying.

Here’s why this mattered so much to the evolutionist project. If human minds work the same way everywhere, then two societies on opposite sides of the planet, with no contact whatsoever, could independently arrive at similar tools, similar rituals, or similar family structures. Evolutionists used this to explain “parallel” developments across unconnected societies without needing to invoke diffusion or historical contact. In fact, the postulate was essential to the great comparative projects of evolutionism, since those projects would have collapsed if cultural differences were assumed to stem from different biology rather than different stages of the same underlying process.

When brains and societies were said to evolve together 🔗

Evolutionists pushed the analogy further by drawing a direct line between biological and social development. As societies grew more complex, they argued, human cognitive capacities were also maturing in step. This is where the theory gets shakier by modern standards: the assumption was that so-called “primitive” societies had less developed mental faculties, and civilization emerged only once minds had developed sufficiently to sustain it. The “germs of thought” that were postulated to account for parallel evolution were meant to explain why different societies, thinking independently, would land on comparable ideas at comparable stages. It’s a tidy theory on paper, but it quietly smuggled in a racial hierarchy dressed up as biology.

One culture with a capital C 🔗

Here’s a subtle but important twist in evolutionist thinking, one the anthropologist Tim Ingold pointed out clearly in his analysis of the school. Evolutionists didn’t really believe in multiple cultures in the plural sense we use today. They believed in a single, universal Culture, and every society on earth was simply occupying a different point along that one continuum. A hunting-gathering group and an industrialized nation weren’t seen as having different cultures; they were seen as being at different stages of the same Culture.

This reframing matters because it explains why evolutionists were so comfortable ranking societies against one another. If there’s only one Culture with one correct trajectory, then comparing societies isn’t disrespectful, it’s just measurement. Any differences you observe are temporal, not qualitative. A society isn’t different, it’s just earlier.

Culture parallels as evidence 🔗

To support this single-Culture model, evolutionists leaned heavily on so-called “culture parallels”: similar tools, myths, or social practices found in societies that had never been in contact with one another. Rather than treating these similarities as coincidence or independent innovation shaped by local needs, evolutionists read them as proof that both societies occupied the same rung on the evolutionary ladder. A stone axe in Africa and a stone axe in the Americas weren’t just similar tools solving similar problems; they were treated as evidence of a shared developmental stage.

Sequential progress and the comparative method 🔗

If societies move through fixed stages at their own pace, how would you even study that scientifically? Evolutionists answered this with the comparative method: instead of tracing one society’s history over centuries, you could simply study different living societies around the world and treat them as stand-ins for different points on the evolutionary timeline. A society still practising hunting and gathering wasn’t just “different,” it was a living fossil, a window into what European ancestors must have looked like thousands of years earlier.

This method needed a fixed reference point, and evolutionists knew exactly where to place it: themselves. European scholars placed their own society at the top of the ladder and measured every other society’s “progress” by how closely it resembled their own institutions, technologies, and family structures. The result was less an objective ranking and more a mirror that always reflected the observer’s own society as the pinnacle.

Meet the armchair anthropologists 🔗

Most of the scholars building these grand theories never actually visited the societies they wrote about. They relied on secondhand reports from missionaries, colonial officials, and travelers, working instead from the comfort of university libraries and studies back home. This earned them the label armchair anthropologists. Even the anthropologist A.R. Radcliffe-Brown, defending the comparative method decades later, acknowledged this history with a wry nod, noting in a well-known lecture that a discipline aiming for systematic comparison must, as he put it, allow space for the armchair. The irony wasn’t lost on later critics, who pointed out that ranking entire civilizations from a desk thousands of kilometres away, using unverified secondhand accounts, was a shaky foundation for a supposedly scientific discipline.

Because these scholars believed societies moved through a fixed sequence, they didn’t worry too much about direct verification. If a society showed traits associated with an early stage, be it particular kinship terms, hunting techniques, or religious beliefs, it was simply slotted into that stage on the universal scale, regardless of its actual, often far more complex, history. As one open textbook on cultural evolution summarizes, the more technologically advanced or educated a society becomes, the more “evolved” it is considered under this framework, a standard that quietly assumes one correct destination for all human societies.

Why this framework eventually fell apart 🔗

It’s worth noting briefly why later anthropologists, from Franz Boas onward, rejected this model so firmly. If psychic unity meant every human mind worked the same way, evolutionists couldn’t easily explain why some societies had “regressed” or why cultural traits didn’t always spread evenly. The comparative method also had no real way of testing its assumptions since it wasn’t built on sustained fieldwork, only on classification from afar. A related open resource on cultural evolution theory notes that psychic unity was treated as dependent on a society’s stage of development, which quietly contradicted the very idea that all minds were equal to begin with. These cracks eventually opened the door to fieldwork-based approaches that replaced armchairs with actual conversations, observations, and lived time among the communities being studied.

Despite its flaws, evolutionism deserves credit for asking a genuinely big question: why do human societies differ so much, and is there any underlying pattern connecting them? The answers it gave were wrong in important ways, shaped more by colonial assumptions than careful evidence, but the question itself has never gone away. It resurfaces in every later school of anthropological thought, just with far more caution about ranking cultures on a single ladder.

What do you think? If psychic unity assumes every human mind works the same way, why did evolutionists still feel comfortable placing some societies above others on their scale? And what does it say about a “scientific” method that was built almost entirely from a desk rather than from time spent with the people being studied?

References

1. https://anthropology.ua.edu/theory/social-evolutionism/
2. https://www.lancaster.ac.uk/fas/psych/glossary/psychic_unity_of_mankind/
3. http://anthrobase.com/Dic/eng/def/psychic_unity.htm
4. https://www.thebritishacademy.ac.uk/documents/2051/pba154p069.pdf
5. https://boisestate.pressbooks.pub/evolutionhumanbehavior/chapter/1-1-history/
6. https://socialsci.libretexts.org/Courses/HACC_Central_Pennsylvania's_Community_College/ANTH_205:_Cultures_of_the_World_-_Perspectives_on_Culture_(Scheib)/03:_Anthropological_Theory/3.02:_Cultural_Evolution