SAMPLINGS 



Genes Well 

 Dropped 



As a species evolves, its genome is constant- 

 ly mutating, and some mutations can inacti- 

 vate a gene. A disaster in the making? Not 

 necessarily. Investigators have discovered 

 that complete gene inactivation, or pseudo- 

 genization, can be beneficial — indeed, an im- 

 portant driving force for evolution. 



Now three evolutionary geneticists have 

 discovered that pseudogenes, or genes no 

 longer expressed as functional proteins, 

 may have contributed to humanity's diver- 

 gence from chimpanzees. Xiaoxia Wang, 

 Wendy E. Grus, and Jianzhi Zhang, all at the 

 University of Michigan in Ann Arbor, identi- 

 fied sixty-seven pseudogenes in the human 



A Room with a Few 



Cockroaches, to the dismay of many apart- 

 ment dwellers, prefer group living. Safety 

 in numbers is one benefit of a gregarious 

 lifestyle, but togetherness can also have its 

 drawbacks — not the least of which is in- 

 creased competition for resources, includ- 

 ing space. A recent study now shows that 

 cockroaches respond to crowding by mak- 

 ing complex collective decisions about how 

 to achieve optimal group size and how to 

 divvy up available nooks and crannies. 



Jean-Marc Ame and Jose Halloy, both 

 biologists at the Free University of Brus- 

 sels, Belgium, and several colleagues pre- 

 sented groups of juvenile German cock- 

 roaches with shelters of varying number 



genome that originated in the time since 

 the human and chimpanzee lineages split. 

 One pseudogene, CASP12, which plays a 

 role in suppressing mammals' immune sys- 

 tems, functions in all mammals except 

 human beings. 



At some point in human evolution, shortly 

 before modern Homo sapiens began to mi- 

 grate out of Africa between 40,000 and 

 60,000 years ago, natural selection began to 

 favor switching off the CASP12 gene. This 

 gene loss reduces the probability of devel- 

 oping severe sepsis, a disease in which the 

 body responds too strongly to an infection. 

 Although exactly how losing the protein 

 that CASP12 encodes can protect against 

 severe sepsis is unknown, clearly, in some 

 cases, less really is more. (P/oS Biology 

 4:0366-77, 2006) —N.W.A. 



and size. When the roaches could choose 

 among several roomy shelters, the entire 

 group piled into a single one. But remark- 

 ably, when one of the shelters couldn't 

 accommodate the whole crowd, the crafty 

 insects distributed themselves into the 

 smallest possible number of equal-size 

 groups. For example, if three shelters were 

 available that could house fifty roaches 

 each, a group of eighty would invariably 

 divide into two groups of forty — not, say, 

 one of fifty and one of thirty, or three ap- 

 proximately equal groups. The insects' so- 

 lution, according to mathematical models 

 developed by the team, benefits all 

 roaches equally and maximally. 



So how do they do it? The 

 group's uncanny behavior appar- 

 ently results from decisions by 

 individual cockroaches. Ame and 

 Halloy posit that when an indi- 

 vidual arrives at a shelter, the 

 more roaches that are already 

 there, the likelier it is to stay. 

 If the space is too crowded, 

 however, the benefits of refuge 

 among its companions are re- 

 duced by the degree of competi- 

 tion for space, and the roach will 

 scuttle off in search of another 

 place to rest its antennae. (PNAS 

 103:5835-40, 2006) 



—N.W.A. 



Catherine Chalmers, 

 Bathroom Window, 2004 



Spectral tarsiers: vicious in mobs 



Harried 

 by the Mob 



When predators are afoot, prey have two 

 options: fight or flight. Defending one's cor- 

 ner might sound honorable, but in a world 

 "red in tooth and claw," honor usually ranks 

 somewhere below self-preservation. So why, 

 asked Sharon Gursky, a primatologist at 

 Texas A&M University in College Station, 

 should spectral tarsiers — tiny primates that 

 weigh just four ounces — risk life and limb to 

 face down a large and potentially lethal 

 snake when they could run away instead? 



The spectral tarsier is a nocturnal primate 

 endemic to the Indonesian island of Sulawesi. 

 Its tree-dwelling lifestyle makes it a target for 

 hungry snakes. But rather than flee the scene 

 when they spot a snake, the tarsiers often 

 make loud calls that attract other tarsiers. 

 The growing mob can swell to as many as 

 ten, and the tarsiers may then spend as long 

 as an hour harassing the would-be predator. 

 Some of the pluckier primates may even dare 

 to strike and bite the snake. The besieged 

 predator typically retreats for cover, but 

 often not before attacking its tormentors. 



Gursky observed natural interactions and 

 carried out experiments with tarsiers and 

 rubber snakes. Most of the tarsier mob, 

 Gursky discovered, belonged to a single so- 

 cial group, but adult males from other 

 groups — often territorial rivals — frequently 

 joined in, particularly when young females 

 were nearby. One possible explanation for 

 the seemingly foolhardy behavior, says 

 Gursky, is that it enables males to demon- 

 strate their prowess and hence their worth 

 as future mates. Faint heart never won fair 

 maiden. {American Journal of Physical 

 Anthropology, 129:601-8, 2006) 



—N.W.A. 



16 



NA'lURAl ins I oky June 2006 



