Recently, much philosophical discussion has centered on the best way to characterize the concepts of random drift1 and natural selection, and, in particular, on the question of whether selection and drift can be conceptually distinguished (Beatty 1984; Brandon 2005; Hodge 1983, 1987; Millstein 2002, 2005; Pfeifer 2005; Shanahan 1992; Stephens 2004).2 These authors all contend, to a greater or l...

AIN and SHEPPARD (1950, 1954) considered that natural selection, in particular visual selection exerted by predators, was an important agent influencing shell color and banding-morph frequencies in populations of Cepaea nemoralis in England. LAMOTTE ( 195 1 ) on the other hand, working with French populations, concluded that selection was of little significance in most colonies, and that random...

woolly poplar aphid, phloeomyzus passerinii (signoret), is considered as an important and serious pest of poplar in iran and many countries. during 2002-2003, resistance and susceptibility of 12 poplar clones to p. passerinii were evaluated in hamedan province of iran. number of formed aphid colonies found in a surface unit was counted three times during a growing season. the clones populus alb...

Salvador Allende Gossens was born in 1908 and died in the coup against his government on 11 September 1973. He was four times candidate for the Presidency—unsuccessfully in 1952, 1958, 1964, and finally successfully in 1970. He qualified as a medical doctor in 1932 but from his student days he was also active in politics, helping to found Chile’s Socialist Party in the same year as his graduati...

When air-dry urediospores of the wheat stem rust, Puccinia graminis f. sp. tritici, are exposed to temperatures below freezing, their germinability is markedly reduced, even after prolonged thawing at room temperature. Germinability is fully restored by a brief heat-shock or by vapor phase hydration. We have found that this "cold dormancy" cannot be reversed once the spores contact liquid water...