Cannibal Canard 



Three years ago a well-publicized study sug- 

 gested that consumption of human flesh might 

 have been widespread among our early ances- 

 tors. New research shows, however, that we 

 may not be descended from cannibals, after all. 



The evidence that cannibalism was once 

 rampant came from a study of elderly women 

 of the Fore people of Papua New Guinea. The 

 women had practiced ritual cannibalism as chil- 

 dren, but they had escaped a disease called 

 kuru that was transmitted by the ritual. (Kuru 

 killed many Fore before cannibalism was 

 banned in the 1950s.) Kuru, like mad cow dis- 

 ease and Creutzfeldt-Jakob disease, is caused 

 by the abnormal development of proteins 

 called prions; in the so-called prion diseases, 

 the abnormal prion proteins cause brain tissue 

 to degenerate. 



Prion proteins are encoded by a single gene 

 known as PRNP, and people with certain varia- 



tions of that gene are resistant to the prion 

 diseases. Indeed, the 2003 study showed, the 

 elderly Fore women were more likely to have a 

 protective gene variation than their kin who 

 never practiced cannibalism. Presumably, most 

 cannibals without the protective gene had 

 succumbed to kuru. Surprisingly, the study 

 turned up the same protective gene variation 

 in people throughout the world, suggesting 

 that prion disease — and by extension, cannibal- 

 ism — was once common. 



But Marta Soldevila and Jaume Bertranpetit, 

 both evolutionary biologists at Pompeu Fabra 

 University in Barcelona, and their collaborators 

 now beg to differ. They examined the PRNP 

 gene of 1 74 people from around the world, 

 and considered all the gene's possible varia- 

 tions — something the earlier study did not do. 

 The team found that the disease-resistant 

 variation of the gene is statistically rare enough 

 to rule out a kuru-haunted past. (Genome 

 Research 16:231-9, 2006) — S.R. 



Cannibals preparing a feast, 16th century 



Worm Sperm 



For some worms, sex is a prickly affair. Dur- 

 ing copulation, specialized bristles on the 

 worm pierce its partner's skin and inject a 

 substance. The role of the substance has re- 

 mained mysterious — but it isn't sperm, which 

 is transferred separately. Now Joris M. 

 Koene, a biologist at Vrije University in Am- 

 sterdam, and his colleagues have solved 

 much of the mystery by removing the bristles 

 of common earthworms and observing what 

 happened when they mated. 



Earthworms, of course, 

 are hermaphroditic. 



The female part of the earthworm, Lumbricus 

 terrestris, includes four so-called sperma- 

 thecae, storage tanks for the sperm they re- 

 ceive. Worms can probably fill their sperm 

 tanks selectively, digesting any unwanted 

 sperm therein. Because they are promiscuous 

 creatures, the process may enable them to 

 choose which of their partners' sperm fertil- 

 izes their eggs. Worms whose mating part- 

 ners were artificially bristle-free, however, ex- 

 erted even greater control: they distributed 

 their partners' sperm less evenly among their 

 four sperm tanks and took in less sperm than 



they would have from normal, bristly mates. 

 The mystery substance, then, appears to be 

 a weapon to override partner choice, and 

 maximize a worm's chances that its sperm is 

 stored and used. 



Darwin thought sexual manipulation by 

 one sex at the expense of the other would 

 not evolve in hermaphrodites, since any in- 

 dividual would simultaneously reap both 

 the gains and the pains. But in fact, sexual 

 manipulation by hermaphrodites is per- 

 fectly compatible with evolution by sexual 

 selection. Once a beneficial sex-specific 

 strategy evolves, any hermaphrodite that 

 has it outperforms those that lack it, and 

 the strategy quickly spreads to the entire 

 population. [Behavioral Ecology and Socio- 

 biology 59:243-9, 2005) — S. R. 



Even hermaphrodites fight the battle of the sexes. 



batalleri, was discovered recently with a false 

 thumb, as well. The digit probably helped the 

 carnivorous panda ancestor climb trees; only 

 later did the red panda's thumb become use- 

 ful for holding bamboo. The giant panda, 

 however, is not closely related to S. batalleri, 

 and its thumb probably evolved indepen- 

 dently. Maybe, for the giant panda, the bam- 

 boo explanation still holds. (PNAS 

 1 03:379-82, 2006) —Nick W. Atkinson 



Scent of a Mushroom 



Organisms that give advance notice to 

 would-be attackers about their toxic de- 

 fenses are no evolutionary paradox: a preda- 

 tor's attack, even if ultimately thwarted, can 

 still harm a poisonous organism. So why, 

 asked Thomas N. Sherratt, an evolutionary bi- 

 ologist at Carleton University in Ottawa, On- 

 tario, and his colleagues, do so many poison- 

 ous mushrooms seem so secretive about 

 their hazards? 



To find the answer, the investigators car- 

 ried out the first formal analysis of the charac- 



teristics associated with poisonous mushroom 

 species in both North America and Europe. 

 They discovered that although poisonous 

 mushrooms aren't generally more colorful 

 than their harmless counterparts, they do 

 have more distinctive odors. One possible ad- 

 vantage of warning by scent (and possibly by 

 taste) instead of by coloration might be that 

 fungivores tend to forage for mushrooms at 

 night, when color vision is less effective than a 

 keen sense of smell. {The American Naturalist 

 166:767-75,2005) —N.W.A. 



March 2006 NATURAL HISTORY 



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