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As well, there are constant aspects of an organism's world in continuous change. No creature lives in isolation from the other life forms that abound in the environment. Organisms interact and co-evolve in complex ways. In the most familiar case of species interaction, the predator-prey relationship, one organism is another’s food. In other cases, organisms affect each other indirectly by modifying their mutual environment, the way beavers produce a good home for frogs by creating a pond. Some of the most common and important relationships in nature are where two or more organisms become entwined in a tightly bound, long-term evolutionary relationship. When the organisms are of different species biologists call it symbiosis; when the interacting creatures are of the same species it is called social behavior. Symbiotic relationships can be parasitic, where one organism benefits to the detriment of another; commensal, where one organism benefits from the relationship and the other is unaffected; or mutual, where all players benefit -- though in the real world these relationships are not so neatly categorized. Domestication, for example, is mutual symbiosis, where one species provides sustenance for another in exchange for hospitable living conditions and reproductive advantages. 

Interdependent organisms evolve in dynamic synchrony with each other over generations, mutual sources of systematic behavior which are embodied in evolving abilities. In the predator-prey relationship, a kind of evolutionary arms race can emerge, where the effective capacities of a predator put pressure on a population of prey to evolve and improve avoidance strategies: speed, visual and olfactory acuity, camouflage, or even group-level behaviors, for example where members of a herd take turns keeping watch while others graze. Improvements on one side of the relationship demand compensatory responses from the other.

In the evolution of mutual symbioses an astonishing range of complex patterns of co-evolution have emerged. Numerous insect and plant species have evolved intricate relationships. There are individual species of fig wasp that have co-evolved exclusively with particular species of fig tree.  Bearing a load of pollen to fertilize the fig, a wasp enters the fruit -- in reality, a flower that evolution has turned inside-out -- to lay its eggs. The fig provides a nursery for larvae which, when they emerge as adults, take a load of pollen with them. Two species working in such an exchange co-evolve very specific interlocking morphological traits. Flowers may have brush-like appendages which apply pollen to pollinators; pollinators may have basket-like structures that carry pollen.

Even more common in nature are symbiotic relationships between complex organisms and microscopic organisms like bacteria, protozoa or fungi, where a large creature becomes the preferred habitat of a small one, which in turn furnishes critical biochemical processes for its host. There are certain microbes found only in specific environments like the digestive systems of termites, where they are responsible for turning wood into usable sustenance.  Cows and other ruminants have evolved a specialized organ, the rumen, that provides a hospitable environment for micro-organisms that break down otherwise indigestible cellulose. One hundred trillion similar microbes inhabit the human digestive system. Many such organisms, in evolving specific interactions with a host, have diverged evolutionarily from their free-living forebears, so that a single species of microbe comes to exist only within a single species of host. Certain bacteria are endemic to the roots of specific plants, which, in exchange for a favorable living environment -- often within the tissues of the plant itself (galls, root nodules) -- provide such necessary nutrients as nitrogen in a chemical form accessible to the plant. Trees have a long-standing relationship with fungi which live in the soil tangled in the roots (occasionally producing the spore-forming bodies we know as truffles). If all the earth’s fungi were suddenly wiped out, plant and animal life would quickly disappear.

The entomologist E. O. Wilson has called ants “the premier social insects.”  Some ants excavate elaborate underground labyrinths of passages and caverns. Different classes of workers fulfilling different functions within the social structure have become anatomically distinct (polymorphic). Ants have also evolved some fascinating symbioses. The leaf-cutter (attine) ants of Central and South America are familiar by their picturesque processions of workers carrying sizable pieces of leaves above their heads like green umbrellas. These ants are notorious in the tropics for their ability to strip the vegetation from a field or a grove of trees with devastating speed. But they do not eat the foliage that disappears underground into the nest. Instead, the leaf pieces are chewed into successively smaller bits by a series of successively smaller worker ants. The macerated leaves are carefully added to the mat that forms a growth medium for a particular species of fungus which breaks down the vegetable matter and grows tiny nutrient-rich structures that form the basis of the ants’ diet. Ant colonies have been found that contain millions of ants, thousands of openings, ventilation shafts and chambers, and hundreds of mold gardens meticulously tended by tiny worker ants. Another participant in the symbiosis is a bacteria with antibiotic properties that lives on the exterior of the ants’ bodies and helps keep the garden free of parasitic micro-organisms -- weeds. In fact, the most common parasite that ants have to contend with is a single species of fungus found only in ant gardens. Ants have been tending their fungal gardens for fifty million years. The most evolutionary modern genus of ants, Atta, maintains a single genetic strain of fungus that has been in use for twenty million years, transported from nest to nest as a pellet in the mouth of the founding queen.  The ants and the fungi keep each other alive.

In The Botany of Desire, journalist and gardener Michael Pollan looks at human agriculture from the point of view of plants. He observes that wild grasses possess the genetic capacity to produce forms, the edible grains, so appealing to humans as to induce them to clear away forests to make way for cultivation. Or as Pollan puts it, “agriculture [is] something grasses did to people as a way to conquer the trees.” 

Perhaps the most widespread and dramatic example of one organism indirectly affecting the evolution of others by modifying the environment is that of the earliest photosynthetic bacteria, which over perhaps a billion years gradually altered the earth’s atmospheric content, making available the oxygen that supports all the numerous and complex forms of aerobic life. 

Clearly, such processes have been absolutely fundamental to the unfolding of planetary life. Evidence of symbiotic relationships which initiated the evolution of cellular complexity billions of years ago is present in every cell of our bodies. Mitochondria, the parts of plant, animal and fungus cells that make energy available for nearly all cellular processes, were once autonomous bacteria with a particular knack for biochemical energy exchange. They formed an allegiance with another simple one-celled organism possessing little inner structure of its own. The bacteria, engulfed but not digested, found safe harbor in a new habitat; the host cell gained a new source of energy. In a process called symbiogenesis a new organism was created from the permanent union of two others. Thus began a new chapter in evolution. Cellular mitochondria possess relics of their former independence in the membrane that encloses them and in a loop of their own genetic material, separate from the DNA within the nucleus of the surrounding cell. Similarly, chloroplasts in green plant cells responsible for photosynthesis were once free-living photosynthetic bacteria that evolved a relationship with another cell, a relationship which became intimate over time until the functions of the two cells were wholly incorporated. The organisms can have no viable independent existence. Conversely, some things that appear to be single organisms are colonies of individuals, as in the case of jellyfish. Lichens, one of the most widely distributed life-forms, are in reality, an intimate alliance between fungi, algae and bacteria that has played a key role in planetary evolution turning rock into nutrient-rich soil for hundreds of millions of years. 

Biological Knowing

A simple organism maintains stability through time embodying structural responses to a small set of the regularities and properties of the world of which it is part. Homeostasis, the collection of processes for self-regulation and maintenance, is anything but static. It is the dynamic means by which a creature maintains its own internal balance with respect to its changing circumstances. It involves interactions between the creature’s functional parts in conjunction with environmental changes specifically relevant to the creature’s survival. Homeostatic functions are sometimes described as being automatic but that doesn’t really do adequate justice to the evolutionary history or the intricacy of the interdependent processes that come together in homeostasis. What is implied is that homeostasis takes place without the necessity of choice or conscious reasoning or knowledge, in our ordinary sense of the word. 

When we talk about knowing we usually reserve the term for relatively complicated creatures with central nervous systems and brains. People know their own names. A dog knows its owner’s smell. A pigeon knows its way home. A penguin chick knows its mother. But what does a jellyfish know? Or a plant? Or a one-celled creature? Or a human blastocyst bathing in amniotic fluid?

The kind of knowing that an organism like a plant does is built into the form and chemistry of its tissues. It can’t identify, remember or deliberate the way people can. The kind of knowing people do -- at least the kind of knowing we know as knowing -- can be conscious, purposeful. Knowing for us is internal, mental, but it is nonetheless physical, structural. 

How do the roots of a dormant plant know it’s spring? Cells in the root respond to changes in moisture and temperature and chemical composition of the soil. How does the plant know that if it starts its annual growth cycle and puts out shoots that break through the surface of the soil into daylight, it won’t meet a killing frost, squandering the stored-up energy that the plant expended on fruitless growth? We might say that it doesn’t know, not for sure. Plants make mistakes. Seasons are variable. It sometimes happens that a late killer frost wipes out spring growth.

But consider the bloodroot, Sanguinaria canadensis, which reliably, every spring, produces one of the first blooms on the forest floor in my nearby (southern Québec) woods. If the resources necessary for its continued survival were depleted beyond a certain point it would be unable to create the structures (leaves with chlorophyll, root systems) it needs to replenish itself and would be unable to reproduce. Yet through years of variable thaws and frosts, this particular configuration of cells that we call sanguinaria has proven flexible enough to accommodate every climactic extreme it has encountered. 

The knowledge a plant possesses has accumulated over two to three billion years of biological evolution. What a plant knows about are aspects of the world that are consistent and relevant to living, like energy and nutrients and defenses against predation. The regularities of the world are inbuilt, inherent in the design of the plant. Living things come into being in collaboration with the world. They are embedded in a consistent world whose regularities are embodied in them. Evolutionary success of an organism can be seen as a successful embodiment, a coherent coupling between a changing organism and its changing world. Survival depends on the cohesion between the organism and its world. 
 
 
 
 

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