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mindfulness exhibited by your slippers, and their respective answers tend to complement each other, resulting in a more complete understanding.
    For the stealthy slippers scenario, the “why?” question has long been settled by the person in whose mind it originated: Philip K. Dick, the prophetic purveyor of philosophical paranoia, which he dressed up as science fiction and sold to pulp publishers to make a living. In the story “The Short Happy Life of a Brown Oxford,” one of Dick’s cartoonish scientist characters introduces a “Principle of Sufficient Irritation,” according to which inanimate objects, such as shoes, can only take so much abuse before they try to do something about it. 2 Before the shoe’s bewildered owner could take up the “how?” question, the newly animate runaway shoe in the story got away in pursuit of a lady shoe love interest, proving the effectiveness of the cherchez la femme cliché in settling the “why?” question in the male-dominated genre that was 1950s sci-fi.
    The truth, however, is often stranger than even PKD’s fiction. Earth’s biosphere is replete with microscopic clumps of organized matter—single cells, such as bacteria or brewer’s yeast, which we tend to regard as hardly more animate than a shoe—that sense, process, and act on outside chemical information, in the service of higher purposes with which shoe-wearing multicellular hulks can readily identify. One such purpose is sustenance: E. coli bacteria, for example, can sense minute directional differences in the concentration of useful metabolites such as aspartate and swim in the direction of the higher concentration. Another purpose is procreation: yeast cells sense and follow pheromone gradients that lead to receptive members of the opposite sex.
    The investigation, then, begins with the big “why” and continues with a series of “whats” and “hows.” Why did a yeast cell cross the road? To get to the block party. How could it tell which way the party was? By sensing where the pheromones were drifting from. What did it need to compute to find that out? The concentration of pheromones in each direction—the direction in which it was higher points to the source. But if pheromone molecules hit the cell and bounce off it, how could it avoid counting the same molecule more than once and getting the direction of the higher concentration wrong? By capturing molecules that hit its specialized pheromone receptors and metabolizing them into some other stuff. (This is the cell’s equivalent of counting items off on its fingers and setting them aside.) 3 And how did it get closer to its prospective mate? By growing a projection, known as a shmoo (I am not kidding), in the right direction.
    Even with unicellular life, there seems to be no end in sight to the march of questions. Entire scientific careers can be (and increasingly are) spent on understanding exclusively some genetic, metabolic, signaling, or structural aspect of life’s minutiae, such as growing shmoos in yeast. Interestingly, however, the very same questions apply, level by level, to all purposive information processors, from a single-cell replicator, propelled by a simple mind to seek a mate, to a considerably more complex replicator whose mind, with tragic foresight, “misgives some consequence yet hanging in the stars” and whose pursuit of happiness is soon checked by fortune’s hand:
    BENVOLIO
    Here comes the furious Tybalt back again.
     
    ROMEO
    Alive, in triumph! and Mercutio slain!
Away to heaven, respective lenity,
And fire-eyed fury be my conduct now!
    Re-enter TYBALT.
     
    Now, Tybalt, take the villain back again,
That late thou gavest me; for Mercutio’s soul
Is but a little way above our heads,
Staying for thine to keep him company:
Either thou, or I, or both, must go with him.
     
    TYBALT
    Thou, wretched boy, that didst consort him here,
Shalt with him hence.
     
    ROMEO
    This shall determine that.
    They fight; TYBALT