By Andrew Klein

Dedicated to my wife, who thought I was a fossil until I started branching out.

I. Introduction: The Lure of the Ladder

Evolution is a ladder.

From “lower” to “higher,” from simple to complex, from primitive to progressive—and we, Homo sapiens, stand firmly at the top. This is one of humanity’s oldest and most persistent narratives. It appears in textbooks, in museum exhibits, and in the very way we view ourselves and others. As Stephen Jay Gould noted, the obsession with this “ladder of progress” is so entrenched that even when we explicitly reject this outdated view of life, we unconsciously fall back into its patterns.

But evolution is not a ladder.

As Gould put it, evolution is a process of “constant branching, sprouting, and producing new twigs.” A ladder is linear; evolution is branching. A ladder has a top; evolution does not. A ladder implies direction; evolution points nowhere.

Gould memorably observed: “We can only linearise a bush when we have only one surviving twig and can erroneously place it at the ladder’s apex.”

This article will dismantle the ladder—and then reveal the bush.

II. The Roots of the Ladder

The ladder narrative predates Darwin by millennia.

It is rooted in the Great Chain of Being (Scala Naturae), a hierarchical system that arranged all living things in a graded order of perfection. It was a non-evolutionary, static model—a snapshot of a fixed, complete whole. It was a ladder of beings, not a story of becoming.

When Darwin appeared, the ladder did not disappear—it was merely temporalised. The line became a timeline. Beings were no longer arranged as “lower” and “higher” in a static hierarchy, but as “earlier” and “later” in a dynamic progression. The result was the “ladder of progress”—a deeply entrenched narrative that evolution is a steady climb toward a predetermined endpoint (us). This perspective is not only false; it is actively harmful.

III. Why the Ladder Is Wrong

1. It Denies Branching.

A ladder is a single line. It implies that at any given time, only one creature is on the path to “progress.” But the reality of evolution is multi-linear. At any given moment, countless branches are extending—and the vast majority of them go extinct.

As evolutionary biologist Steven Pinker succinctly put it: “Evolution doesn’t make ladders; it makes bushes.”

2. It Confuses Ancestors with Cousins.

The ladder narrative encourages the error of treating modern species as if they are each other’s ancestors. But chimpanzees are not our ancestors—we are cousins. We share a common ancestor, and that ancestor is extinct. Life is a branching bush, not a chain of inheritance.

3. It Fosters the “Primitive Lineage Fallacy.”

Biologists themselves fall into the trap of interpreting phylogenetic trees as ladders, assuming that lineages that branched off early and are species-poor are “primitive” or “ancestral.” This cognitive bias is known as the primitive lineage fallacy. Its harm lies in reinforcing the idea that species that survive are “successful” and those that go extinct are “failures“—obscuring the fact that extinction often results from random events or environmental shifts.

4. It Fabricates Teleology.

A ladder implies direction. It implies that evolution is moving toward something—and that something is us. But evolution has no goal. It has no direction. It is merely the process of populations reproducing and dying in response to changing environments. As Gould observed, the ladder “compresses evolution’s immense diversity into a single scheme defined by a single time and place.”

IV. The Truth of the Bush

The ladder is a misunderstanding. Evolution is a bush—a bush that constantly branches, sprouts, and has most of its twigs pruned by the “shears of extinction.”

4.1 The Bush in Palaeontology

In 2025, the discovery of new fossils revealed a new hominin species, helping to transform the picture of human evolution from a linear ladder into a more tree-like form. Multiple hominin species coexisted at the same site, proving that human evolution is “less linear and more tree-like.”

As a PNAS special feature noted, a central question has been “whether early human evolution is better described as a ladder or a bush.” The reality is that palaeoanthropology is full of “dead twigs“—side branches that left no descendants. The Neanderthals are one such example. Since 1910, several more dead twigs have been discovered and incorporated into reconstructions of the human family tree.

Gould concluded that life is not a ladder-like success story with humans at the top, but is better understood as a bush in which the “modal bacterium” is the “constant paradigm of success” in life’s history.

4.2 The Bush in Development and Learning

The ladder narrative is entrenched beyond biology. We tend to imagine development as a linear process—from fertilised egg to adult, step by step.

But the brain does not develop like a ladder. It develops like a bush.

Neural development is characterised by the generation of dendritic branches and synaptic organisation. Neurons do not simply grow in a straight line—they branch and retreat, exploring possible synaptic partners and retaining or pruning connections based on activity patterns. During development, dendrites repeatedly add and retract branches. Neural connections are overproduced and then pruned—a bush being shaped, not a ladder being climbed.

“Neural constructivism” suggests that mammalian neocortical evolution has moved towards more flexible representational structures, rather than increasing innate specialised circuits. There is no preset ladder—only a bush that constantly adapts and reorganises.

4.3 The Bush in Culture

Human culture is also governed by bush-like patterns. Languages do not evolve linearly from a single source; they form a bush of branching, contacting, and merging. Technologies do not develop in a straight line from simple to complex—they form a bush of experimentation, failure, and branching.

V. Why the Ladder Matters

You might ask: “Does this matter?”

Yes. Because the ladder is not merely an incorrect model. It is a dangerous one.

The ladder narrative provides justification for hierarchy. It implies that some beings (and some groups of people) are inherently “superior” to others because they are “more advanced.” It implies that progress is linear and that those who are “behind” have simply not caught up yet. It provides ideological cover for colonialism, racism, and the exploitation of others.

The bush narrative does the opposite. It shows that:

· We hold no special place in the tree of life.

· Our existence is contingent, not destined.

· Extinction is the norm, not the exception.

· Evolution has no direction and no endpoint.

The bush narrative is humbling. It reminds us that we are just one twig on a vast, ancient bush—sharing the same soil, the same roots, and the same fate as all the other twigs.

VI. Conclusion: Embrace the Bush

The ladder obsession is outdated. It is nested within the old Great Chain of Being model, reinforced by the “ladder of progress,” and consolidated by the “primitive lineage fallacy.” It denies branching, confuses cousins with ancestors, and fabricates teleology.

The bush is the truer model. It is supported by evidence from palaeontology, developmental neuroscience, and cultural evolution. It is more humble, more accurate, and ultimately more useful.

It is time to put down the ladder. It is time to embrace the bush.

It is time to recognise that we are not the apex of evolution—we are one branch, flourishing for this moment, among many.

Andrew Klein

References

1. Gould, S. J. (1991). Bully for Brontosaurus: Reflections in Natural History. Evolution is not a ladder but a bush — Gould’s collected essays.

2. Gould, S. J. (1976). Ladders, Bushes, and Human Evolution. Natural History. Should human evolution be described as a ladder or a bush.

3. Omland, K. E., Cook, L. G., & Crisp, M. D. (2008). Tree thinking for all biology: the problem with reading phylogenies as ladders of progress. BioEssays, 30(9), 854-867. The problem of reading phylogenetic trees as ladders — the primitive lineage fallacy.

4. Villmoare, B., et al. (2025). Discovery of new fossils and a new species of ancient human ancestor reveals insights on evolution. EurekAlert. New fossil discovery shows human evolution is more tree-like than ladder-like.

5. PNAS Special Feature: Issues in human evolution. Whether early human evolution is a ladder or a bush.

6. Pinker, S. (2009). Cognitive Luck: Substance Concepts in an Evolutionary Frame. “Evolution doesn’t make ladders; it makes bushes.”

7. Neural constructivism and dendritic branching studies. Branching and synaptic organisation in neural development.

8. Nature (1992). Origin and evolution of the genus Homo. Simple linear models of human evolution are no longer tenable.