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.No real alien will have a recognisableEarthlike lineage: no reptiles, no vertebrates, nothing terrestrial-parochial in its ancestry.So we will not be able to understand itsbiology.Indeed, we can t really understand the tricks, like proton-pumps, which our own mitochondria use and which are crucial forevery aspect of sub-cellular metabolism.Not for bacteria, however,because they don t have mitochondria: instead, they have a suite ofspace elevators of their own.We list a few of the bolas/space elevator tricks used by terrestrial life,to show you the scope and scale of what we might expect in otherevolutionary histories:" Cell membranes, which have proteins laced through them, so thatpushing a receptor button on the outside rings a chemical bellinside;" Tubulin, a fibre-assembled and disassembled protein, is used tomove other molecules, and chromosomes, around;" Antifreeze proteins are used by Arctic and Antarctic fishes to stoptheir body fluids freezing;" Mammals use the dangerous technique of hanging their testes out-side the body, to keep them cool enough to produce functionalsperm.Look at that familiar last example another way: to remain warmer andquicker than your prey/predator, you need your muscles to be warmer165 WHAT DOES A MARTIAN LOOK LIKE?than your testes can bear but the risk is clearly worth it.But what dohot females do, then? There is accumulating evidence that mammalianovaries are at body temperature, but their Graafian follicles, with eggsinside them, are chemically cooled by about 2.6ÚC.Any alien lifeform will have lots of cute tricks like those, not at allobvious and not at all transparent, because they will be exploiting tricksthat aren t in our well-investigated lifeforms.Those tricks expand thephase space of potential alien lifeforms in ways that are totallyunimaginable.The well-investigated lifeforms are actually only a tinyproportion of terrestrial organisms: think, for a start, of all those extinctspecies.But our lifeforms must have thousands of tricks, which may beexpressed only in a rare deep-sea prawn that hasn t had buckets ofcancer-cure money spent on it to understand the clever and unique waythat it repairs its DNA faults or whatever.We know only a tinyfraction of our terrestrial biology.A different, alien, evolutionary treemay be only marginally more mysterious, in that we will understandvirtually none of it without a lot of work.Some people who have thought about these matters are very unsurehow many alien lifeforms will fit our criteria for life, even though thesehave broadened considerably in the last twenty years! Prions,crystallised viruses, a bacterial economy in the deep rocks, which mightbe comparable in mass to all Earth s marine life; these have stretchedour understanding of our own global ecosystem in innumerableunexpected directions.In 2000, Russell Vreeland and colleaguesreported that they had isolated bacterial spores, preserved in salt crystalsfor 250 million years, and that these came back to life when placed ona standard agar culture medium.The researchers took stringentprecautions to avoid contamination.The bacteria were of an unknownspecies, but their DNA was similar to that of the modern speciesBacillus marismortui and Virgibacillus pantothenticus.Simple lifeforms seem to be virtually immortal.And the same goesfor some more complex creatures, for instance tardigrades, often knownas water-bears.These are about a millimetre long, and are found onsphagnum moss in swamps on mountainsides, and in the muck in rain-gutters.They can withstand drying-out, boiling, and a variety of otherusually lethal insults.Some species can survive at temperatures close toabsolute zero and well above the boiling point of water.They remain166 THE EVOLUTION OF ALIEN LIFEalive (or potentially so) for 1000 years, if dried out: just add water.More generally, biological development is itself a space elevator:instead of growing then dividing, growing then dividing, as mostprokaryotes do, most larger organisms have a succession of stages thatthey pass through before they produce a creature that can then producethe spores, eggs, or sperms for the next generation.You may think thatour reproductive sequence egg ’!blastocyst ’! implant ’! embryo’!fetus ’!baby ’! infant ’! toddler ’!adolescent ’! adult is fairlycomplicated.Not so: some marine creatures have twenty or moredifferent shapes and ways of life to follow their developmentaltrajectories.And they also have branches, with several differentpossibilities often to become male or female, for example, according tocircumstances, like our fictional Europan caretaker.These tricks do not alter the universals of xenobiology: they areeither parochials, or they exploit universals by novel routes.This meansthat on a planet with a similar history to ours, we would still be able torecognise which creatures are the higher lifeforms, despite parochialdifferences and local biological space elevators.The creepy-crawlieswould probably look similar to ours, to the untutored eye, too.Indeed, the variety seen in such creatures here is immense, and manyterrestrial organisms look distinctly alien.Pycnogonids so-called sea-spiders look like incredibly emaciated spiders: they tuck their gutsinto their limbs because there isn t room in the tiny body.Some morayeels, which live in coral, are a hundred times as long as they are thick
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