I am reminded of the movies about aliens from other planets living among us by a remarkable article by Elizabeth Pennisi in the November 18 issue of Science entitled “An Evolutionary Classic.” Excerpts from the article:

An army ant colony does not welcome outsiders. Not only are the ants notoriously fierce, but they specialize in coordinating mass attacks. Yet within the nests of all 340 known species of army ants, quietly stealing nourishment from their unwitting hosts, live tiny beetles. These flea-sized parasites have lost their “beetleness” and look, smell, and behave so much like their ants that they can pilfer food or eat ant young with impunity.

Recent studies “show that the beetles adapted to live with army ants not once, as some investigators thought, but at least a dozen times. Similar “parallel evolution” usually occurs in species who are relatively closely related so they can use a similar genetic tool box. The rove beetle species, in contrast, had already been diverging for tens of millions of years before they took up independently with army ants. “It is a textbook example of morphological convergence,” says Terry Ord, an evolutionary biologist at the University of New South Wales in Sydney, Australia. “It is likely to become a classic.”

The common ancestor of the parasitic lineages had already evolved a gland at the tip of the abdomen that squirts noxious compounds called quinones at any attackers. It’s a preadaptation that allows you to undergo some extreme adaptations. Since then, some parasitic beetles have evolved new glands and new functions. One group now sprays ant alarm pheromones that cause would-be attackers to scatter. Others secrete what are likely the same chemicals that ants themselves use to recognize colony mates. With the help of still other features, including a narrowed waist, longer legs, antennae with antlike elbow joints, and even an antlike gait, the interlopers effectively fool their hosts into feeding, protecting, and transporting them.

Parasitic Aliens
Rove beetle on the right (Photo by Takashi Komatsu)

The ecological niche that these rove beetles exploited is the abundance produced by the cooperative social structure of ants (and termites, which beetles have also invaded). Although they are represented by fewer than twenty thousand of the millions of known living insect species, ants and termites compose more than half of the world’s insect body weight. The closest analogue parasitic invader into the human ecology are domesticated animals, particularly dogs, who have evolved to mimic us not physically but mentally and emotionally. Emotions in humans are analogous to smell (pheromones) in ants: in our evolutionary past, hominins communicated with their emotions.

Alien InvadersSimon Conway Morris, a Cambridge professor, is best known for his detailed and careful study of the fossils of the Burgess Shale, and for the scientific concept of Cambrian explosion. The results of these discoveries were celebrated in Wonderful Life (1989) by Stephen Jay Gould. More recently, Dr. Conway Morris has become the leading authority in this phenomenon of “morphological convergence.” He is interested in the constraints that are placed on nature, such that there is only one solution to certain ecological niches as illustrated above. His thinking runs counter to one of the “cannons” of current evolutionary theory that all is based on chance and evolution can only be intelligible in retrospect. I believe that the transformation from a social structure based on dominance and submission in apes to one based on obedience to group authority in hominins would be similar, and therefore a convergent transition in other higher forms of life in the universe; as Professor Conway Morris points out, the existence of convergence make the possibility of other intelligent life in the universe more likely.


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