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.The background ismade up of individuals, but those individuals are evolving because ofthe game they play against that background, so the scenery evolves alongwith the players.You may be surprised that we haven t mentioned DNA here,especially given the selfish gene view that an organism is merely avehicle for the replication of DNA, with the gene being the true unitof natural selection.In The Collapse of Chaos we argued against theselfish gene viewpoint, which we saw as a needlessly narrowinterpretation of a much broader and more interesting complicitybetween DNA and organisms, between genotype and phenotype.If itwere true that the genome of an organism determines every feature ofits body-plan and behaviour, then it would be reasonable to adopt agene-centred viewpoint.However, many other things go into makingan organism, and most of them depend on context.The genome plays a very subtle role, but its most important effect isto lubricate evolution, not to control it.DNA makes it possible fororganisms to change from one generation to the next: it makesphenotypes fluid , able to respond to a changing environment.Whatdetermines the form and behaviour of those organisms that survive toreproduce is natural selection, and this acts on organisms; its action onDNA is very indirect and very cryptic.The dynamical flow inphenotypic space how species change in their evolving ecosystems is an emergent feature of a complicity between organisms, theirgenetics, and their environmental context.The unit of evolution mustbe ecosystems, because those are the main context for everything else,themselves included.156 THE EVOLUTION OF ALIEN LIFEIt is therefore much more difficult to understand whether theecological evolutionary route followed by Earth s early triploblasts feeding and producing faeces would be available on another planet,than it is to compare anatomical/functional adaptations and classifythem as parochial or universal.Evolution is about populations oforganisms specialising into ecosystems and making new niches waysto make a living for themselves.There is rarely an empty niche fororganisms to exploit, except by the accident of transport to a new land,like rats, goats, rabbits, deer, gorse, Japanese knotweed, Canadianpondweed, and a thousand other alien species introductions.Organisms complicate their ecosystem, and the ecosystem constrainsand evolves the organisms, much as a river winds across the landscape,changing the local geography but having its own path determined bythe substrates it finds.So, on other aqueous planets, the familiar things will happen on thelevel of ecosystems.We will find ecological system-architectures thattranslate directly into architectures that we know from our own world,with predators and prey, herbivores, grasses with tough leaves fedupon by specialised grazers, trees with the ability to catch any lightthere is and to shade other plants.But we cannot know whether those trees , like so many of ours, will encourage birds to build their nests ,and fertilise the tree roots with minerals from afar; or whether the grasses will, as they have done here, prevent lakes and ponds lastingvery long, by growing in from the edges.Presumably they willsometimes do those things, in some places and on some planets.Fromour experience of Earth, we won t expect to find desert planets likeHerbert s Dune (Arrakis) or jungle planets like Harrison sDeathworld; in most eras, most planets will have diverse ecologies indifferent places, because that is a universal.Over the last twenty years a whole new view of evolution has arisen controversial, but fascinating, and with a solid core of good sense: itlooks like a universal, and it should therefore apply to alien ecosystems,if suitably generalised.This is James Lovelock s concept of Gaia , of theEarth (and, by extension, any alien ecology) as a self-regulating complexsystem.To call Earth an organism in its own right, as some do, is totake the idea too far or possibly not far enough, for Earth s157 WHAT DOES A MARTIAN LOOK LIKE?organisation is different from that of any single living creature.TheGaia view of evolution is now widely accepted, as regards its basis that the environment is controlled by feedback from the organismsevolving in it.Some New Age romantics claim that Gaia is conscious ofthis process, but this extra dimension has few adherents amongscientists.Gaian evolution requires the fostering of heterogeneity, for examplethe diversification of life on to the land and the invention of whole newways of life, such as dinosaurs, trees, and insects.Whether it is possiblefor one species to take over an ecology and turn it into a monoculture,as has been suggested by several authors, like Gerrold in his Chtorrseries, is not yet clear.The reverse seems to be the major theme inevolution here, but monocultures do seem to work in limited regions ofEarth, so perhaps they never got a real chance to strut their stuff on thisworld.(Maybe Gaia stopped them.) Our ecology diversifies and themost complex organisms grow ever larger and ever more complex.Thismust be a universal, but surely not the universal.We are in good company in not considering the larger contextualevolution the evolution of ecosystems on Earth as progressively morecomplex creatures come into existence [ Pobierz całość w formacie PDF ]