The Bushy Tree

By Andrew Klein

Dedication: To my wife – who has always known that the strongest branches are those that bend toward one another, not those that stand alone.

“For decades, textbooks showed a single file: Australopithecus → Homo habilis → Homo erectus → us. That image is a myth – a neat story imposed on a messy reality. The real story is a bush. Many branches. Some lead nowhere. One eventually leads to us. The branches did not compete in a gladiatorial arena – they co‑existed, sharing the landscape, eating different foods, avoiding or ignoring each other.”

I. The Myth of the Ladder

For generations, the story of human evolution was told as a triumphant march: a single line of descent, each species replaced by a more advanced successor, culminating in Homo sapiens – the pinnacle. This image – the “March of Progress” – is one of the most recognisable and misleading icons in science.

The truth, now confirmed by fossil discoveries that would have seemed impossible a generation ago, is far more interesting – and far more relevant to how we live today.

The human family tree is not a ladder. It is a bush. A sprawling, branching, sometimes messy tangle of species that overlapped, coexisted, and in some cases, interbred. Our ancestors shared the landscape with other humans – not as a single triumphant lineage, but as one branch among many.

At the Ledi-Geraru site in Ethiopia’s Afar region, researchers have found fossil evidence that early Homo and a previously unknown species of Australopithecus lived side by side nearly 2.6 million years ago. The famous “Lucy” species had disappeared from the region by 3 million years ago. But another Australopithecus persisted – and overlapped with our direct ancestors.

“People often think evolution is a linear progression,” explains anthropologist Lucas Delezene, “like the March of Progress, but in reality, humans are only one species that make up a twig of a bigger family tree – it’s quite bushy… The idea that Homo appears and immediately spreads around the planet and replaces all other hominin species is not accurate. Homo lived side-by-side with many other hominin species throughout Africa”.

II. The Bushy Tree

Today, Homo sapiens is the only surviving hominin. But in the past, we were not alone. There are now 21 known species of human in the fossil record. Our ancestors may have encountered as many as eight different human species, from the robust and stocky Neanderthals and their close relatives the Denisovans, to the small-brained but culturally complex Homo naledi.

This diversity was not a problem to be solved. It was a strategy.

Different species adapted to different niches. Paranthropus evolved massive teeth and chewing muscles for a diet of tough, fibrous plants. Homo developed larger brains and, eventually, stone tools and a more flexible diet. Neanderthals adapted to cold climates, their stocky bodies conserving heat. Denisovans thrived across Asia, leaving genetic traces still present in modern populations.

They did not eliminate each other. They coexisted – sharing the landscape, eating different foods, sometimes interbreeding, sometimes ignoring each other. The image of a gladiatorial arena, where only the strongest survive, is a projection of modern anxieties onto an ancient past that did not work that way.

“Where did our compassion come from? We didn’t learn it from watching lions.”

III. The Prehistoric Evidence for Coexistence

The evidence for overlap is now overwhelming.

· At Ledi-Geraru, Homo and Australopithecus overlapped between 2.6 and 2.8 million years ago.

· In southern Africa, early Homo overlapped with Paranthropus in multiple regions.

· Neanderthals and Homo sapiens overlapped in Europe and the Middle East for tens of thousands of years – and not only coexisted, but interbred. The DNA of every non-African human today contains between 1% and 4% Neanderthal ancestry.

· The Denisovans, known mostly from a finger bone and a jaw, left their genetic mark in populations from Siberia to Southeast Asia.

One of the most stunning discoveries came in 2025: the identification of “Denny” – a girl with a Neanderthal mother and a Denisovan father. She was not a hybrid of two separate species in the way we think of species today. She was simply human. Her bones were found in a cave in Siberia, thousands of kilometres from where her parents’ lineages supposedly lived. They met. They mated. They raised a child.

This is not the story of a ladder. This is the story of a bush.

IV. Kindness as an Evolutionary Advantage

The popular imagination of human evolution is dominated by violence: men hunting, tribes fighting, the strong dominating the weak. But the fossil record tells a different story. It tells a story of care.

Ancient skeletons show remarkable signs of survival from illness and injuries that would have been impossible without help. A broken leg that healed. A jaw without teeth, kept alive by someone who chewed food for them. A skull that had survived a devastating injury, the bone healed, the person still alive years later.

The evidence of compassion extends back one and a half million years. Scientists have traced medical knowledge to at least the time of the Neanderthals.

What was the evolutionary advantage of this?

Altruism kept the group together. It allowed older members to pass on knowledge – where to find water, which plants were poisonous, how to survive the winter. It kept skilled hunters alive after accidents. It bound communities in webs of mutual obligation that made them stronger than any individual could be alone.

The species that learned to care for its vulnerable outlasted the species that left them behind.

V. The Danger of Exclusivity: Sparta and the Violence Trap

If diversity is strength, then exclusivity is a slow poison. The historical record is filled with societies that defined themselves by who they excluded – and paid the price in demographic collapse.

Sparta is the classic case. At its peak, the Spartan citizen population numbered perhaps 9,000 Spartiates – a ruling elite that dominated some 160,000 helots (slaves) through systematic violence. The famous krypteia – the “Hidden” – was a state-sanctioned terror organisation whose members hunted and killed helots who showed any signs of standing out from the mass.

The Spartan system was stable for centuries, but only by a brutal logic. Rents extracted from the helots were distributed proportionally to each Spartiate’s capacity to commit violence. This “proportionality principle” kept the elite in check – no one had an incentive to disrupt the system. But it also trapped Sparta in a violence trap: rents could not be redistributed in more economically productive ways without destabilising the regime.

The result was a society that was stable but low-performing. And, crucially, demographically doomed. By the time Sparta faced its final defeats, the citizen population had collapsed from 9,000 to fewer than 1,000. The system that had sustained them – based on exclusivity, violence, and the rigid exclusion of outsiders – had consumed itself.

Sparta did not fall because it was conquered. It fell because it ran out of people. The lesson is clear: exclusivity is a demographic dead end.

VI. The Modern Warning: Israel’s Demographic Crossroads

The same pattern can be observed today. A society that defines itself by who it excludes – and that relies on violence to maintain that exclusion – faces predictable long-term consequences.

Israel, a state built on the principle of Jewish exclusivity, is now at a demographic crossroads. According to the Taub Center’s State of the Nation Report 2025, for the first time since its founding, Israel’s population growth rate has fallen below 1% – to just 0.9%.

This is not a temporary fluctuation. It is a structural shift:

· Fertility rates are declining in all sectors – secular Jewish, religious, and Arab – and are expected to continue falling.

· The number of deaths is projected to rise by 77% by 2040 as large cohorts age.

· Net migration turned negative in 2024 – more people left Israel than arrived – and is expected to stay negative through 2026.

The migration shift is particularly striking. The current wave of emigration is not only among non-native-born Israelis. There is a steady upward trend in emigration among Israel-born Israelis as well. Destinations are diversifying: fewer are moving to traditional destinations like the US and Australia; more are choosing Germany, Cyprus, and East Asian countries – a search for lifestyle change rather than purely economic reasons.

The OECD has also noted that Israel faces significant long-term fiscal pressures from demographic shifts, particularly the rising share of population groups with weaker labour market attachment.

Prof. Alex Weinreb of the Taub Center concludes: “We are at the beginning of a new era in Israel’s demographic development. The peak period of natural increase has passed, alongside a less stable – and even negative – migration balance. This represents a clear break from past patterns”.

The exclusivity that defined the state’s founding logic is becoming, in purely demographic terms, unsustainable. This is not a matter of politics or ideology. It is arithmetic.

Exclusivity, in the long term, does not preserve a people. It diminishes them.

VII. The Pattern Is Not New – But the Stakes Have Changed

What we see in Israel is not unique. It is the latest iteration of a pattern that has repeated across history: societies that define themselves by rigid boundaries of belonging – by blood, by faith, by ethnicity – eventually face demographic decline, emigration, and collapse.

The difference today is the scale of the consequences. A collapsing Sparta affected the Peloponnese. A collapsing state in the modern Middle East, armed with nuclear weapons and locked in perpetual conflict, affects the entire world.

The response to this reality cannot be to double down on exclusivity. It must be to open – not only borders, but imaginations. To recognise that diversity is not a threat to be managed but a strength to be cultivated. To understand that societies that welcome outsiders, that integrate difference, that see variety as a resource rather than a danger, are the societies that endure.

VIII. What the Research Tells Us

The scientific evidence is clear across multiple fields:

Biology: Species diversity arises through adaptation to different resources, not through elimination of competitors. The finches of the Galápagos did not become multiple species by killing each other – they adapted to different food sources. The human bush is the same pattern writ large.

Anthropology: The fossil record shows coexistence, not constant warfare. “The idea that Homo appears and immediately spreads around the planet and replaces all other hominin species is not accurate,” says Delezene.

Sociology: Research on multicultural societies consistently shows that diversity, when managed with policies of inclusion and equal opportunity, strengthens social cohesion rather than weakening it. The counter‑evidence – the claim that diversity leads to conflict – is largely drawn from societies where diversity is imposed without equity, or where elites deliberately stoke ethnic tensions for political gain.

Demography: Exclusivity is a demographic dead end. From Sparta to the present, societies that close themselves off from the world – that refuse to integrate, that define belonging by blood alone – face inevitable decline.

IX. The Garden, Not the Ladder

Creation is not a ladder. It is a garden. Many branches, many experiments, many species that flourished and faded. The resonance does not care about linear progress. It cares about diversity, about adaptation, about the slow, branching, beautiful unfolding of possibility.

Those who see the world as a gladiatorial arena – as a zero‑sum competition where one group’s gain is another’s loss – have not understood evolution. They have projected their own fears onto a past that was far more cooperative, far more mixed, far more human than they imagine.

The ladder was a myth. The bush is real.

And the only way to survive – as a species, as a society, as a state – is to stop climbing the ladder and start tending the garden.

Andrew Klein

Selected Sources and References

· Ledi-Geraru fossil discoveries – Delezene, L. et al. “New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia.” Nature, 2025.

· Bushy human family tree – Spikins, P. Hidden Depths: The Origins of Human Connection, 2022; University of York.

· Spartan demographic collapse – Doran, T. Spartan Oliganthropia, Brill, 2018; Ober, J. & Weingast, B. “The Sparta Game,” in How to Do Things with History, Oxford, 2018.

· Israeli demographic crossroads – Taub Center for Social Policy Studies, State of the Nation Report 2025; OECD, Long-Term Spending Projections in Israel, 2025.

· Darwin’s finches and adaptive radiation – Beausoleil, M-O. et al. “The fitness landscape of a community of Darwin’s finches.” Evolution, 2024.

· Multiculturalism and social cohesion – Reitz, J.G. et al. Multiculturalism and Social Cohesion: Potentials and Challenges of Diversity, Springer, 2009; Povinelli, E. The Cunning of Recognition, Duke University Press, 2002.