“…At a more subtle level, it is an important determinant of mating success. That individual differences in activity are substantially under genetic control is already well established (Ewing, 1963;Connolly, 1963;Hay, 1972;Angus, 1973;van Dijken and Scharloo, 1979a;van Dijken et aL, 1979). There are some difficulties in interpreting what the measured activity represents in these investigations which differ in the methods of observation employed, because no distinction has been made between the amount and speed of locomotor activity.…”