The Flamingo’s Smile by Stephen Jay Gould

respectability, and Mabel. But he was formally bound until his twenty-first birthday , and he was born on February 29. “You are a little boy of five,” the Pirate King informs him with glee and expectation of prolonged service. The three principals of the Pirates of Penzance then analyze the complexities of this predicament in the famous paradox song:
    How quaint the ways of paradox
    At common sense she gaily mocks.
    The classic paradox presents us with two contradictory interpretations, each quite correct in its own context. Consider our western prototypes, the so-called paradoxes of Zeno: The arrow that can never reach its destination because, at any instant, it must occupy a fixed position; and Achilles who will never catch the tortoise because he must first traverse half the remaining distance, and any gap, no matter how small, can still be halved. We delight in paradox because it appeals to both the sublime and whimsical aspects of our psyche. We laugh with Frederic, but also feel that something deep about the nature of logic and life lies hidden in Zeno’s conundrums.
    Biology too has its classical paradox. It flared as a major issue in the nineteenth century, probably because scientists then felt that they might find a resolution. All the best naturalists struggled in vain: Huxley and Agassiz lined up on opposite sides; Haeckel tried to mediate. The twentieth century has largely bypassed the conundrum, probably because we now realize that no simple answer exists. Yet, if our fascination with paradox be justified, the question can still enlighten us by virtue of its stubborn intractability.
    Physalia , the Portuguese man-of-war, embodies all this fuss. It is a siphonophore, a relative of corals and jellyfish. The old paradox addresses an issue that could not be more fundamental—the definition of an organism and the general question of boundaries in nature. Specifically: Are siphonophores organisms or colonies?
    Siphonophores belong to the phylum Cnidaria (or Coelenterata). Two aspects of cnidarian biology set the context of our paradox. First, many cnidarians live as colonies of connected individuals—our massive coral reefs are gigantic congeries made of many million tiny, conjoined polyps. Second, the cnidarian life cycle features a so-called alternation of generations. The sessile polyp, a fixed cylinder with a fringe of tentacles, reproduces asexually and generates by budding the free-swimming medusa, or “jellyfish.” The medusa produces sexual cells that unite and grow into a polyp. And so it goes.

    A Portuguese man-of-war. The creature is a colony, not a single organism. The float is a medusa person, and each “tentacle” is a polyp person. FROM LOUIS AGASSIZ’S MONOGRAPH (1862), REPRINTED FROM NATURAL HISTORY .

    T.H. Huxley’s 1849 illustration of the Portuguese man-of-war. He regarded this creature as an individual, not a colony.
    Different kinds of cnidarians may emphasize one of these generations and suppress the other. Of the three major cnidarian groups, the Scyphozoa (or true jellyfish) have abandoned polyps and emphasized medusae, while the Anthozoa (or true corals) have dispensed with medusae and constructed reefs of polyps and their skeletons. In the third group, the Hydrozoa, many members retain the full cycle, with prominent polyp and medusa. Siphonophores are hydrozoans. The technical literature, not usually noted either for charm or directness, has transcended its usual limitatons in this case: amidst a forest of formidable jargon for other parts of cnidarian anatomy, it refers to the polyp and medusa stages of a single life cycle as “persons.”
    The Portuguese man-of-war, with its float above and tentacles below, looks superficially like a jellyfish (that is, a single medusa). When studied more carefully, we find that this floating weapon is a colony of many persons, both polyps and medusae. The pneumatophore, or float, is probably a greatly modified medusa (though some scientists