The Long War

know your parents; you received no parental care. Their young may not be guided through family backgrounds and formal education as we are. Perhaps they compete for a right to live, and part of that competition is learning how to make tools. But that means every generation must more or less reinvent the culture from scratch.’
    ‘Hmm. Thus limiting their overall progress, generation to generation. Maybe. That is a lot of supposition based on just a little data.’
    Roberta had learned not to say things like It’s too beautiful a theory not to be true . Once Jacques Montecute, overstressed, had told her that she should have the slogan ‘Nobody Likes a Smart Alec’ tattooed to her forehead in reverse, so she could be reminded of it every morning in the bathroom mirror. She contented herself with saying, ‘It does fit with the likely physiology, and the evidence of the non-uniformity of the tools. But, yes, the theory needs more testing. It would be interesting to know what’s going on nearer the equator in this world.’
    Yue-Sai did a double take. ‘Why so?’
    ‘Because those tortoises that solved the mazes back on the Datum were allowed to do so in warm conditions. Tortoises are cold-blooded; they shut down in the cold, to some extent.’
    ‘Oh. So maybe the behaviour we’re witnessing here, in the cold, is—’
    ‘Limited by temperature. They may be achieving much more in warmer latitudes. Do you think Captain Chen would sanction a journey south, towards the equator?’
    ‘And risk getting shot down by some super-tortoise? I do not think so.’ Yue-Sai packed away her equipment. ‘Time to get back to the ship.’
    Before they left, Roberta glanced across the valley, to the far wall where erosion had exposed the strata of the local sedimentary rocks. She could clearly see a marine deposit, a chalky layer embedded with flints, below a bed of gravel, and then above that a few yards of peat, under the mossy ground surface. She could read the geology. This region, now elevated, had once been under the sea. Later, ice had come and gone, leaving behind the gravel, and then the peat had been laid down over millennia of temperate climates . . . This world, like all other worlds, had a story of its own, a story billions of years deep and probably not quite like any other in the Long Earth ensemble. A story that probably nobody would ever get around to unravelling, and all she would take away from this place was a few snapshots of tortoises.
    She could only turn away.
    Back at the airship Captain Chen was excited, and not about tortoises. ‘Finally – finally! – we have the results back from the probes we sent into the Eastern Gap. You remember, more than six million worlds back.’
    ‘Of course I remember.’
    ‘You asked us to inspect the planets, Venus and Mars. And the scientists found—’
    ‘Life.’
    He seemed crestfallen. ‘You knew? Of course you would know . . .’
    On the Mars of the missing Earth East 2,217,643, there was oxygen and methane in the air, chemically unstable gases that must have been injected by the processes of life. There seemed to be some kind of vegetative covering on the lower ground of the northern hemisphere. And in the clouds of that copy of Venus, high, cool, full of water, chlorophyll had been observed. Earth-like plants, drifting in the Venusian sky.
    No, Roberta wasn’t surprised. Any Gap that could be reached by a stepping animal, even the most foolish of humanoids, was going to be a place where bacteria and other living organisms were regularly injected into space, if only accidentally, through the hole where Earth should be. Most such reluctant pioneers would die quickly, including the hapless humanoids if they couldn’t step straight back – but some hardy bacterial spores, having hitched a ride on the stepping humanoids, might survive the radiation, the vacuum. And of those spores, some might ultimately drift into the skies of other worlds, and seed them. This was panspermia, the transfer by natural processes of life between the worlds. It was thought to be possible even in the Datum universe. How much easier panspermia must be in a Gap cosmos, with a way for life to reach space so much more easily than being blasted off by an asteroid impact.
    No, Roberta wasn’t surprised. She filed the confirmation away in the back of her mind, where a kind of model of the Long Earth, and all its facets, was slowly being assembled, fact by fact, deduction by