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works as a whole. If any step in the provisioning and oviposition process is omitted, the whole operation may fail.

For societies with this level of organization, it is no wonder that the claim for organismal status of groups has sometimes been made (Seeley, 1989; Wheeler, 1911). If this claim stands up to scrutiny, it is extraordinary in two ways because we think of organisms as consolidated units in two senses: they are both physically contiguous and genetically uniform.

An organism is typically one solid, connected mass. If it is a single cell, it is bounded by a membrane; if it is multicellular, the cells abut one another and form a discrete larger unit. If a social insect colony is an organism, however, it is a divided one, with parts (the individuals) freely moving past each other and only occasionally coming into direct contact. Other organisms with separated parts are known. A lizard may detach its tail to save itself from a predator, and the tail continues to twitch, distracting the predator long after the main body of the lizard has escaped. Similarly, when a honey bee worker stings a foe, the barbed sting can easily detach from the honey bee’s body, and when it does, the sting continues to dig into the victim’s skin and the poison sac continues to contract and deliver more of its venom. But these detached organs act independently for only a brief time before expiring. Moreover, these parts are clearly secondary, in the sense that a joining of trunk and tail did not form the lizard. Instead, tails are normally attached parts of the organism, both in the lizard itself and in its relatives with nondetachable tails. A social insect superorganism, on the other hand, is built from the very beginning of detached parts. Physical attachment is rare and ephemeral, such as when army ant workers interlock to form a sheltering bivouac.

A typical organism is also genetically homogeneous. Again, social insect colonies differ from this standard. In the simplest colony structure, all members are offspring of a single queen and her mate, so they share many genes, but each receives its own unique combination of parental genes. In other species, this genetic distinctness is exacerbated by the presence of multiple queens or multiple mates. This genetic structure is utterly different from the clonal, mitotically derived set of cells that constitute a typical multicellular organism (Maynard Smith, 1988). Given that natural selection operates by favoring genes that pass copies into the next generation, it is little surprise that a clonal entity can evolve cooperation. If social insect colonies lack this unity of genotype, what gives them the unity of purpose that makes them an organism rather than a contentious flock?

HOW ARE COLONIES ORGANISMAL?

It is not hard to view a termite castle, an army ant bivouac, or a wasp colony as a single, coordinated organism. Each shows division of labor,



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