s pathogenicity.) theor Biol 232: 17-26. 77. Keenan EL, EP Stabler (2005). Linguistic invariants and language variation. In Logic, Methodology and Philosophy of Science, ed. P Hajck et al. London: Kings College Publications, 395-411. 78. Lee Y, T Collier, C Taylor, EP Stabler (2005). The role of population structur