5. 1. 1 Biological Rhythms and Clocks From an evolutionary perspective, the adaptation of an organism s behavior to its environment has depended on one of life s fundamental traits: biological rhythm generation. In virtually all light-sensitive organisms from cyanobacteria to humans, biological clocks adapt cyclic physiology to geophysical time with time-keeping properties in the circadian (24 h), ultradian (24 h) domains (Edmunds, 1988; Lloyd, 1998; Lloyd et al., 2001; Lloyd and Murray, 2006; Lloyd, 2007; Pittendrigh, 1993; Sweeney and Hastings, 1960) By definition, all rhythms exhibit...