Edward O. Wilson was, first and last, a zoologist — a student of whole organisms, and above all of ants. Yet his vision of biology was never confined to the study of animals in the field. He came of age as the molecular revolution was transforming the life sciences, he fought to defend organismic biology against its ascendancy, and he spent much of his career insisting that the many branches of biology — molecular and organismic, genetic and ecological, the study of the cell and the study of the ecosystem — belong to a single connected science. This final chapter of the reader traces Wilson's engagement with the life sciences beyond his home ground of zoology: his reckoning with molecular genetics, his fascination with the vast and largely unexplored world of microbial life, his understanding of development and the brain, and his enduring conviction that biology, for all its internal divisions, is ultimately one. The molecular wars at Harvard and their aftermath are recounted in Chapter 15, and the levels-of-organization framework that underpins Wilson's whole philosophy of biology in Chapter 13; here the subject is Wilson's substantive reach into the other life sciences, and his vision of their unity.
Wilson's relationship to genetics was foundational, for the science of social behavior he built rested squarely on the mathematics of the gene. However much he championed the whole organism against the reductionists, Wilson grounded his own theoretical work in population genetics — in the rigorous analysis of how selection, mutation, migration, and genetic drift change the frequencies of genes in populations over time. The evolutionary explanations at the heart of his sociobiology depended on this genetic foundation: the theory of inclusive fitness, which explains the altruism of sterile workers, is a genetic argument, turning on the sharing of genes among relatives, and Wilson worked out its consequences using the peculiar genetics of the ants and their relatives (treated in Chapter 5). He drew, too, on the mechanics of heredity at the finest scale — on genetic mutation as the ultimate source of the new variation on which all evolution depends, on the founder effects by which small colonizing populations carry only a limited sample of their parent population's genes, and on the distinctive haplodiploid genetics of the Hymenoptera, which makes sisters unusually closely related and may help explain the repeated evolution of insect societies. For all his defense of the organism, Wilson was no enemy of the gene; he simply insisted that genes must be understood in the context of the organisms and populations in which they act.
Wilson also drew on genetics in his most controversial domain, the study of human behavior, where he marshaled the evidence of heredity against the doctrine of the blank slate. Studies of twins and of adopted children, he argued, demonstrate that heredity influences human personality and temperament, not merely physical traits — that the genes shape not only the body but the disposition, contributing to the differences among individuals and to the shared features of human nature alike. Yet Wilson was careful, here as elsewhere, to qualify his hereditarianism and to guard against its misreading. Genes, he insisted, prescribe tendencies and capacities rather than fixed and inevitable behaviors; they set predispositions and biases, not destinies, and they express themselves only through development in an environment, so that nature and nurture are inseparable partners rather than opposing forces (this reframing is developed in Chapter 26). The genetics of behavior, in Wilson's hands, was thus a subtle instrument, affirming the reality of genetic influence on the mind while denying the crude determinism his critics attributed to him. He wanted a behavioral genetics that took heredity seriously without reducing human beings to the mere expression of their genes — that recognized, as he put it, the genetic leash on human nature while insisting that the leash was long and flexible.
If genetics gave Wilson his theoretical foundation, it was the microbial world that most captured his sense of biology's unexplored frontiers. Wilson was endlessly fascinated by the little things that run the world — not only the insects he had made his life's study, but the still smaller and more numerous world of microorganisms, the bacteria and other microbes whose diversity and abundance dwarf that of all visible life. He emphasized what he called the bacterial frontier, the vast black hole of unknown microbial diversity, arguing that the number of bacterial species on Earth is essentially unknown and enormous, and that this microbial world constitutes one of the greatest unexplored realms of the biosphere, as poorly charted as the deep sea or the rain-forest canopy. The hidden realms of microbial life, Wilson insisted, hold a diversity that dwarfs the familiar world of plants and animals, and their exploration was, for him, one of the great frontiers of biology — a domain where the scale of human ignorance was vast and the potential for discovery immense. His famous injunction to attend to the small and overlooked things of nature applied with full force to the microbes, the most numerous and metabolically versatile organisms on the planet, and the true foundation of the biosphere's chemistry.
Wilson drew from this a general principle about the relationship between size and diversity: that biological diversity increases as one descends the scale of life, because smaller organisms find far more niches in which to specialize. A single tree, or a handful of soil, or the gut of a single insect, contains a multitude of microscopic habitats invisible to the human eye, each capable of supporting its own distinct forms of life; and so the smaller the organism, the more finely the living world is partitioned, and the greater the number of species it can contain. This insight reversed the intuitive human tendency to measure the importance of organisms by their size, directing attention instead to the small, the numerous, and the overlooked, where the true bulk of biological diversity resides. It was of a piece with Wilson's lifelong conviction that the little things — the insects, the microbes, the countless small organisms that most people never notice — are the ones that run the world, performing the ecological work on which the visible world of large plants and animals entirely depends. To understand the diversity of life, Wilson insisted, one must attend above all to the small, for it is there, at the scale of the insect and the microbe, that the living world's variety is concentrated.
Wilson also brought a physiological and developmental sensibility to his understanding of how organisms are attuned to their world. Living things, he observed, come to anticipate nature's rhythms, their life cycles timed by evolution to the recurring patterns of their environment — the seasons, the rains, the cycles of day and night — so that the behavior encoded in their genes is exquisitely matched to the physical world in which they evolved. This attunement, written into the organism through the long action of natural selection, revealed to Wilson the depth of the connection between the living thing and its physical setting, and the extent to which the biology of any organism can be understood only in relation to the environment that shaped it. It exemplified, too, his conviction that the different levels and branches of biology are ultimately inseparable: to understand why an organism behaves as it does, one must understand its genes, its development, its physiology, its evolutionary history, and its ecological setting, all at once, as facets of a single integrated whole. No single specialty, Wilson believed, could capture a living thing entire; only the connected biology he championed, spanning every level from the molecular to the ecological, could do justice to the full reality of life.
Wilson's interest in the microbial world was not merely a matter of cataloguing its diversity; it reflected his understanding of how deeply the fate of larger organisms is bound up with the activities of the small. He was keenly aware of the pervasiveness of symbiosis — of the intimate partnerships between larger organisms and their microbial associates on which so much of life depends. The termites he studied, for instance, cannot themselves digest the cellulose in the wood they eat; they depend utterly on the gut-dwelling microbial symbionts that break it down for them, a mutualism that lies at the very foundation of termite ecology and success. Across the living world, Wilson recognized, such partnerships between the large and the microscopic are the rule rather than the exception, and the visible organisms of the biosphere are sustained by an invisible microbial infrastructure without which they could not survive. This attention to symbiosis connected Wilson's zoology to microbiology at the most fundamental level, revealing the animals he studied as composite beings, dependent on and inseparable from the microbial life within and around them.
The deepest expression of Wilson's engagement with microbiology lay in his understanding of the great evolutionary transitions by which complex life arose from simple, and above all the origin of the complex cell. Life on Earth began with simple microbes, and for most of its history consisted of nothing else; the emergence of the eukaryotic cell — the complex cell with a nucleus and specialized organelles, around 1.8 billion years ago — was a pivotal advance that opened the way to all larger and more complex life (its place in the history of diversity is treated in Chapter 25). Wilson embraced the now-established understanding that this transition was itself a product of symbiosis: the eukaryotic cell arose when simpler cells merged in cooperative union, one engulfing another and the two coming to live and reproduce as one, so that the organelles of our own cells are the descendants of once free-living bacteria. This endosymbiotic origin of the complex cell held a special significance for Wilson, for it was, in his account, one of the great early triumphs of cooperation in the history of life — an instance of the same principle, the merging of formerly independent units into a higher-level whole, that he saw at work in the origin of the ant colony and of human society (this theme is developed in Chapter 17). The story of the cell, for Wilson, was of a piece with the story of the superorganism: at every level, life advances by cooperation, by the union of the smaller into the greater.
Wilson's reach extended, too, into the sciences of development and the brain — the fields that trace how a single fertilized cell becomes a complex organism, and how the organized matter of the nervous system gives rise to behavior and mind. He drew on developmental biology in his account of how the same genome can produce dramatically different forms, as when genetically identical insect larvae develop into queens or workers depending on their nutrition and circumstance, and in his discussion of the canalization of development, the tendency of development to reach species-typical outcomes across a range of environments, and of the critical periods during which certain experiences must occur if development is to proceed normally. And he engaged, increasingly in his later work, with neuroscience — with the emerging science of how the mind arises from the brain. Wilson embraced a thoroughgoing biological account of the mind, tracing the higher properties of human thought and feeling to the physical operations of the evolved brain, an organ shaped by natural selection to promote survival and reproduction (this psychology is developed in Chapter 18). The advances of neuroscience, which were beginning in his lifetime to locate the machinery of thought, emotion, and perception in the circuitry of neural tissue, he welcomed as the fulfillment of his conviction that mind is a biological phenomenon, continuous with the rest of nature and explicable, in principle, by the same methods that illuminate every other feature of life.
Underlying all these engagements was Wilson's abiding conviction that biology, for all its internal divisions, is fundamentally one science — a single connected structure spanning the levels of organization from the molecule to the ecosystem. He understood evolution as operating across the whole range of these levels, from genetic changes within populations up through the emergence of new species and the large-scale patterns of macroevolution, and he insisted that the forces driving change at each level must be integrated into a coherent account of how the diversity of life arises. He was aware of the debates among biologists over which level — the gene, the individual, the population, the species — should be given precedence as the fundamental unit of selection and explanation, and he engaged those debates throughout his career. But his deepest commitment was to the connection of the levels rather than the triumph of any one of them: to the vision of a biology in which the molecular and the organismic, the genetic and the ecological, are understood as complementary perspectives on a single living reality, each illuminating a different level of an unbroken chain that runs from the gene to the biosphere. The living world, Wilson wrote, is a vast biochemical laboratory, in which millions of species have evolved countless chemical and biological solutions over billions of years — a single, connected enterprise of life, to be understood whole.
This vision of a unified biology was, in a sense, the disciplinary expression of Wilson's whole philosophy of knowledge. Just as he sought to connect the sciences to the humanities in the grand program of consilience (treated in Chapter 20), so within biology itself he sought to connect the fragmented specialties — molecular biology and ecology, genetics and behavior, the study of the cell and the study of the ecosystem — into a single coherent science. He had lived through the era in which molecular biology, in its first flush of triumph, had seemed poised to absorb or displace the older organismic biology, and he had fought to defend the study of whole organisms and whole ecosystems against that reductive ambition (recounted in Chapter 15). But his aim was never the victory of one kind of biology over another; it was their reconciliation, the recognition that the molecular and the organismic are not rivals but partners, each indispensable to a complete understanding of life. Wilson lived to see this reconciliation substantially achieved, as molecular methods were absorbed into evolutionary and ecological biology and the artificial opposition between the levels gave way to a more integrated science. The unity of biology, which he had defended in its darkest hour, became in his later years an increasingly evident reality.
Wilson's reach into the life sciences beyond zoology thus reveals, in a final and fitting way, the synthesizing vision that unified his entire career. The zoologist who had spent his life in the field with the ants was also a population geneticist, a student of the microbial world, an advocate of the reconciliation of molecular and organismic biology, and a prophet of the unity of the life sciences. He refused to be confined to a single level or a single method, insisting always on the connections that run through the living world and through the science that studies it. The gene and the organism, the microbe and the ecosystem, the molecule and the mind — all were, for Wilson, parts of a single connected reality, to be understood not in isolation but in relation, as levels of one unbroken chain of life. It was the same conviction that had animated all his work, from the theory of island biogeography to the vision of consilience: that the deepest understanding comes from connecting what has been kept apart, from tracing the threads that bind the disparate phenomena of nature into a single fabric. In the life sciences as in all else, Wilson sought the whole — the unity beneath the diversity, the connection beneath the specialization — and he left, as his legacy to biology, the vision of a science as unified and as interconnected as the living world it seeks to understand.
And so the reader closes where Wilson's science began and ended: with the conviction that life is one. From the ants of his Alabama boyhood to the microbes that run the world, from the genes that encode heredity to the ecosystems that sustain the biosphere, from the evolved brain to the diversity of life across the whole planet, Wilson pursued a single vision of biology as a connected and unified science — and, beyond biology, of all knowledge as ultimately one. The chapters of this reader have traced that vision across its many domains: the social insects and the theory of their societies, the islands and the biodiversity they revealed, the evolution of social behavior and the nature of humanity, the philosophy and the conservation and the creativity that occupied his later years, and the reach of his thought across the disciplines into the earth sciences, the humanities, the economy, and the whole of the life sciences. Through all of it runs the thread that this reader has followed: the conviction, held from first to last, that the living world is a single interconnected whole, that the human species is wholly a part of it, and that to understand life — in all its diversity, from the gene to the biosphere — is the highest calling of the human mind and the surest foundation for the preservation of the living world on which our own existence, and the existence of all we cherish, finally depends.