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Chapter 1 None of the dramatic and sweeping changes that influenced the biological world in the latter part of the 19 th Century, was more profound than the writings of Charles Darwin. He gave biology a theory that lent understanding to the widely and popularly hel d vie w o f th e time , tha t lif e i s a n eterna l struggle, re d i n fan g an d claw , wit h onl y th e strongest , hardiest and fleetest surviving — the remainder but fodder or meat for the successful. Such crassness was not his view of life , bu t i t wa s th e wa y hi s finding s wer e popularl y interpreted. Animals were regarded as being in competition, with survival of the fittest leading to the natural selection of those characters that contributed to that fitness. Fitness is not simply the ability to kill everything else—it can be manifest in many ways. Selection may enhance reproductive success, so that a greater percentage of young survive in comparison with those of your competitors. Large size, as with elephants, can take you into a size refuge from predation, or team cooperation as with the Musk Ox can enhance group survival. We no w kno w tha t natura l selectio n operate s i n a multitude of ways, at a variety of levels and over the whole of earth's space and time to sustain a natural world in which the various components interact, to greater or lesser degrees, in th e maintenanc e o f a dynami c equilibrium . True , catastrophic events in the earth's history temporarily adjust the equilibrium but these can be viewed in much the same way as a forest fire — temporary aberrations that stimulate rebirth, recolonization an d th e re-establishment o f a new hierarchy that ultimately rejoins the world of the whole. The wor d 'symbiosis ' wa s coine d i n 1879 , b y th e French naturalist de Bary to describe a category of animals which live in association with each other. Usually one of the partners is larger than the other, has a more or less passive role in the association, and is called the host, while the active partner or partners are smaller and are referred to as symbionts. The discovery tha t such association s did not seem t o fal l within the 19t h century concept of internecine strife held peculiar fascination fo r biologists and still does. As more research is undertaken, the extent to which these associations truly reflect the more usual way of life for many animals and plants is becoming better appreciated. Upon reflection, such examples are well known to us all (as they were to Charles Darwin): insect s pollinatin g flower s an d th e exoti c adaptations and extents to which such plants have gone to ensure their attractiveness for this purpose. The advantages accrued by both members of this association, albeit rarely involving mutual residence, are obvious. So intimate is the association tha t suc h flower s an d insect s ar e use d a s a n example of co-evolution. Similarly we are also aware that our domesticated animals live in a kind of symbiosis with us and in this knowledge we know of yet another association — that of the fleas and ticks which periodically plague our pets and require our help in their eradication. Parasitism i s an extreme example of symbioti c associatio n an d ma y hav e arisen by several different routes: through refinement of the classical predator-pre y relationshi p o r throug h a simple r symbiosis wher e on e partne r invasivel y exploit s a mor e primitive, commensall y o r mutuall y advantageous , relationship. As this book will illustrate, partnership associations are much more common and diverse than most non-biologists are aware and nowhere is this more marvellously seen than in the sea. Because of television and a natural interest in the living underwater world, many readers will be aware already that the sea provides us with many examples of associations —the sucker-fishes or remoras that attach to the undersurface of sharks , rays an d eve n turtle s t o periodically sli p thei r anchorage and share the host's meal. Many will know of the brilliantly coloured and amusing clown fishes that live...

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