magazine article: Theosophy in Australia, June 2006.
Transcript of talk at TS Convention in Melbourne Jan 2006.
The theme of this Convention includes “non-violence and peace”, and so it is appropriate to investigate the extent and character of symbioses in nature. The book “Liaisons of Life” by biologist Tom Wakeford (John Wiley & Sons, 2001) provided the major source of data and is highly recommended for further study.
The term “symbiosis” covers a spectrum of associations where unrelated organisms live together in varying degrees of intimacy. All gradations exist from free-living organisms to mutualists and to parasites. In fact, social relations in natural societies are as varied as those in human ones. In both, there exist conflict and parasitism, or partnership and mutual benefit.
Biological alliances are dynamic and “As in the more plastic of human relationships, casual associations may pass over into mutually helpful partnership, or transform partnership into parasitism. How difficult it may be to distinguish between service and slavery” (Wells & Huxley, 1929, quoted in Wakeford, 2001 p.185).
In traditional Darwinism, the origin of new characteristics and species was attributed primarily to competition. T.H. Huxley strongly promoted the idea that “Nature is red in tooth and claw”. With regard to bacteria, Louis Pasteur saw all “germs” as hostile to life. However, in reality, pathogenic microbes are the exception and not the rule. The vast majority of bacteria live harmlessly and unobtrusively in seas and soils; many are essential to the production and digestion of foods, and the recycling of wastes. Microbes and their interactions are fundamental to the origin, evolution, and current function of every creature we encounter.
Even before Darwin’s death, many biologists recognised that permanent associations between organisms were widespread and not necessarily harmful. The term ‘parasitism’ was inadequate and a new word ‘symbiosis’ was created. Darwin was aware of the interdependence between organisms, and this was part of his concept of the “struggle for existence”. He more frequently used the words “domestication” than “competition”. Such ideas have now been incorporated into the concept of “biodomestication” whereby plants (for example) nurture nutritionally good microbes, and inhibit infectious organisms.
As early as 1853, biologist Anton de Bary realized that the intimate association of microbes with plants and animals were just as likely to lead to mutual dependence and innovation as they were to mutual destruction. Symbiotic lichens could then be considered along with other associations previously believed to be parasitic.
In the twentieth century open hostility to symbiosis came from politically minded biologists who equated the concept with the ideology of communes and with Communism. In contrast, during the 1930s & 40s Allee & Emerson of USA showed that evolution was not merely a war of survival, and that ethical principles had their parallels in nature. They believed that organic evolution progresses from conflict to cooperation and toleration. Just as a cell in the body functions for the benefit of the whole organism, so the individual becomes subordinate to the larger population.
By 1963, a special congress on symbiosis revealed overwhelming evidence for the common association between members of different biological kingdoms, the persistence of most symbioses, and their profound consequences for evolution. Microbes were identified as the new building blocks of biology – the atoms of this symbiotic revolution.
Simple and Complex Cells
Prokaryotes (or bacteria), simple cells that lack nuclei, evolved first over 3,8 billion years ago, whereas eucaryotes (cells with nuclei) are more complex, appearing some 1.5 billion years ago. These include all animals, plants and lichens. In 1967 Lynn Margulis explained the origin of eukaryotic cells and of sexuality by the incorporation of various bacteria into larger nucleated cells. Margulis used the term “symbiogenesis” for the transformation that took place as bacterial ancestors of mitochondria (energy transformers) and chloroplasts were incorporated into other bacterial cells, and after prolonged symbiotic association, became permanent and heritable.
Lichens and Plants
Lichens are a symbiosis of two different kinds of organism: algae and fungi. Lichens are very tough. They live under extreme conditions, surviving even the hostility of spacetravel. They were the first to colonize the land. Over 90% of plants host mycorrhizal (root) fungi, and hence are products of similar evolutionary mergers. These tiny living fungal threads extend meters beyond their associated plants. They take up mineral nutrients like phosphate and distribute them throughout the fungal body. In exchange for supplying the plant roots with such nutrients, the fungi receive sugars produced by the plant’s photosynthesis.
Most plants have domesticated their own species of fungus. A single interconnected energy network of fungi is often shared between several different plants. Such a dynamic underground interdependence constitutes a “guild” or super-organism – one in which new ecological and evolutionary processes can occur.
Rhizobia are the only group of bacteria that can rival the power of fungi to form a dynamic duo with plants. These are the legumes, the second largest plant group, including acacias, peanuts, and most beans. The legume roots form nodules where bacteria have infected them. These fix the nitrogen from the air and provide nitrates to the plant and surrounding soil. The legume, in turn provides copious amounts of sugar to its rhizobia.
Symbioses are Common
The widespread use of the electron microscope in the 1960s, led to the detection that most insects contain communities of bacteria inside their guts. Microbes do many things from detoxifying chemicals and synthesizing essential amino acids to breaking down cellulose and recycling nitrogen. While genes are important to evolution, they are not the sole mechanism of change. Bacteria can clearly transform insects as well. In many cases microbial symbionts have been integrated into every stage of insect life cycles.
Many symbioses have evolved into domestication, where one partner has cultivated its own particular microbe. Orchids domesticate their fungi to supply nutrients to their roots without harming the rest of the plant. Corals have evolved their domestication by swapping the microbes they cultivate, depending on the surrounding environments.
The masters of domestication are termites and leaf-cutter ants: they have devised the ultimate system of fertilizing, weeding, and even breeding their microbial crops to an extent that makes our own modern methods look biologically primitive. Domestication is thus a powerful concept in evolutionary biology because as one organism alters the environmental context of another, the two associates together may become a new interdependent unit. Once domesticated, microbes can provide novel ways of obtaining resources for both parties. Together, the two organisms comprise an emergent individual whose origin and essence is interdependence.
To conclude, in the vast scheme of evolution, there exist varying degrees of co-operation from loose alliances to domestication and to intimate interdependence. The very existence of such symbioses indicates that they have survived the prolonged challenges presented by nature’s often harsh environmental battles. Cooperation is thus shown to have been as important as competition.