The Soil Beneath Our Feet May Drive Evolution, Two Naturalists Argue

On a sunny December morning in 2010, at the Presidential Estate of Castelporziano near Rome, two naturalists met beside a soil profile and stumbled into one of the most provocative conversations in modern ecology. One of them, soil scientist Augusto Zanella of the University of Padua, was kneeling in a hole in the forest floor, holding two handfuls of earth. The other was Sandro Pignatti, the legendary Italian botanist whose monumental Flora of Italy remains a cornerstone of European plant science. Their meeting, later reconstructed in an article published in the journal Italian Botanist, was not a conventional research paper but a free-flowing dialogue about evolution, death, and the possibility that soil is not merely the stage on which life unfolds, but an active participant in it. The exchange, they argue, may help bridge the long-standing divide between vegetation scientists and soil ecologists, two communities that study the same landscape from opposite ends.

The conversation began, fittingly, with a classification problem. Zanella was holding a zoogenic organic horizon, called zoOH, litter transformed into humus largely by arthropods, and an organo-mineral A horizon, called meA, made of stable aggregates between one and four millimeters in diameter produced by earthworms. In an orderly soil profile these horizons sit neatly one above the other, but wild boars rooting through the litter with their snouts had scrambled the sequence entirely. Zanella joked that classification systems would need new categories to handle such chaos. Pignatti smiled and offered a broader lesson: field scientists arrive with clear ideas, then the messy reality of nature blurs them. The encounter set the tone for everything that followed, an attempt to reconcile tidy scientific frameworks with an ecosystem whose boundaries refuse to stay still.

Walking through a holm oak forest dotted with circular pools of stagnant water, the two men turned to the discipline of phytosociology, the classical Braun-Blanquet tradition of mapping plant communities using characteristic species. The problem, they agreed, is that these diagnostic species by definition have narrow ecological ranges, which makes them scarce precisely along the boundary lines where cartographers need them most. Mapping plant landscapes without leaving large unclassifiable gray areas is nearly impossible. Pignatti described himself not as a phytosociologist but as an expert in vegetation ecology, and recalled that the late Lucio Susmel had written a well-documented critique of the phytosociological approach as early as 1959. Yet in the field, both men admitted, even skeptics are forced to imitate the phytosociologists, reading the colors and structure of vegetation to recognize units within a landscape.

Their shared conclusion was subtle. Plant communities may be real, evolving and shifting entities whose members, in Pignatti’s words, communicate with each other and with animals simply to survive, yet they remain poorly defined in space, existing like objects in a kind of black hole shaped by ecological attractors that themselves keep changing. This echoes Tansley’s foundational 1935 concept of the ecosystem and its crucial insistence on indivisibility: when we try to understand ecological functioning, we cannot separate living beings from each other, nor any organism from its environment. Ecosystems, the two naturalists argued, should in principle continue evolving into the future, though human interference has made recent evolution unnatural for at least a century. Where that trajectory leads, no one can say.

The heart of the dialogue, and the idea most likely to raise eyebrows, concerns what happens underground. Zanella described what he calls a double soil: the familiar one beneath plants, and a second, less visible one inside the bellies of animals, because animals too must digest the food they gather. In both places, pedofauna and microorganisms transform necromass, the dead material of previous generations, into building blocks usable by new life. What emerges is a cyclical process of death and renewal that Zanella suggests we may mistakenly label biodegradation. Death, in this view, is not the end of biological function but its recycling engine, continuously and progressively renewing the soil and enriching the sources of structural building blocks on which every generation depends.

Pignatti pushed the idea further, proposing that small fragments of DNA might travel to new generations outside the known reproductive pathway. DNA exists outside cells, free in the environment or stored in organic matter, like words in a vocabulary accumulated across successive generations. He suggested that such an environmental flow of genetic material could help explain observed co-evolution, the existence of non-coding DNA, and the puzzling presence of DNA belonging to organisms other than the one that houses it, findings documented in the scientific literature of recent decades. Zanella found the notion electrifying: evolution would involve not only sexually transmitted DNA but the genetic traffic of an entire co-inhabiting community, flowing through the soil in confined digestive processes of death and recycling, dynamic, fluid and unpredictable, branching within the limits imposed by the environment and, today more than ever, by humanity.

From there the conversation turned boldly speculative. Zanella noted that when gametes fuse into a single diploid cell, they partially die, and asked whether reproduction itself might be understood as a consequence of cell death, one cell swallowing another to form a new one. Decomposition and reproduction, he suggested, could be two faces of the same process, a perpetuation of the soil’s logic at the cellular scale, with mitosis and meiosis perhaps acting as miniature recycling mechanisms. He even invoked the famous Miller-Urey experiment of 1959, pointing out that the primordial soup from which life emerged could be read as a primordial soil, or even a primordial cell. Pignatti responded with a unifying image: a transmitted language of DNA fragments, a thread connecting all living beings that still eludes us, and a reminder that Darwin arrived at natural selection without knowing anything about DNA at all.

Crucially, the dialogue is not pure speculation. The authors point to a growing body of published research supporting the functional importance of soil processes in evolution. Studies show that soil microorganisms in natural environments can have lower biodiversity indices yet be more biologically and physiologically connected to one another than those in neighboring anthropized ecosystems. Nitrogen fertilization has been shown to significantly reduce soil bacterial diversity, with stronger effects in cropland than in grassland or forest. Polyspecific meadows make better use of environmental resources than monospecific ones, and a single exogenous species can generate an entirely new ecosystem. Microscopic imaging of a single organo-mineral aggregate from an Andosol reveals interdependent flows of minerals and organic matter driven by biological activity that varies with rainfall, each aggregate functioning as a miniature soil. The pattern that emerges is of living beings organized into functional groups, each serving as a cog in a clock-like system, giving transformed resources to others in order to receive modified resources in return.

This functional perspective carries a sober warning. Simply assembling many species together raises biodiversity counts but does not automatically create a functioning system; such artificial assemblages, if allowed to evolve, tend to drift back toward functionally connected configurations. When humans destroy a natural ecosystem, they eliminate a historical web of biological and physicochemical interdependences that is largely unknown and therefore nearly impossible to reconstruct. The authors’ framing recalls the pioneering Gaia-inspired work of Lovelock and Margulis, extending it to the suggestion that species never evolve alone: it is the ecosystems containing them that evolve, with them, within a hierarchy of nested systems from the cell to the universe. On this reading, Homo sapiens may be just one link in the chain, and a species’ so-called finality always recedes into a changing future.

The excursion ended with an object lesson in ecosystem unity. Within a few meters, the Castelporziano forest shifted from an ash woodland with laurel growing on fresh soil over impermeable clay, to an oak woodland of Turkey and Frainetto oaks on sandy, filtering ground, and the entire ecosystem changed with it, soil and vegetation together. Over sandwiches, Zanella asked Pignatti how he had managed the Flora of Italy; the answer, a house full of plant lists in notebooks scattered along the stairs and shelves, and a network of tireless collaborators, was delivered, the author notes, like a hero. The dialogue they recorded is an invitation to reflect on the meaning of life by considering the functional contribution of death, and on the possibility that the spiral of plants, soil, and recycled DNA turns beneath us still, one of nature’s oldest and least understood engines of evolution.

Subject of Research: The role of soil as a living recycling matrix in evolution, DNA flow, and ecosystem function

Article Title: The spiral of plants and soil in the cycle of life

Article References: Zanella, A. (2024). The spiral of plants and soil in the cycle of life. Italian Botanist, 17, 1-11. https://doi.org/10.3897/italianbotanist.17.107071

Image Credits: AI Generated

DOI: 10.3897/italianbotanist.17.107071

Keywords: soil ecology, evolution, phytosociology, humus, DNA recycling, ecosystems, soil biodiversity, vegetation science, Castelporziano, decomposition, Sandro Pignatti, Italian Botanist