Fig. 7. Unidirectional evolution in response to selection. Evolutionary change measured as the difference in population means between generations, x, with changes grouped by absence (N=5) and presence (N=4) of selection. Selection occurred in generations 1, 5, 6 and 9; chance occurs throughout. Neither of the genetically based traits, E and L, evolved unidirectionally in response to selection. The four components of fitness, R, t, U and W, evolved unidirectionally in response to selection. Navigational prowess increases in response to selection, while tail stiffness k does not. Significance determined using one-way ANOVA on data transformed to create normal distributions (logL, k; arcsine R, U, W, NP; inverse t). Values are means ± s.e.m.