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.
The Theosophical Society in Australia