“…Such selection has been investigated theoretically (Wright, 1935;Robertson, 1956;Latter, 1960;Curnow, 1964;Singh and Lewontin, 1966;Gale and Kearsey, 1968) and experimentally (Falconer, 1957;Thoday, 1959;Prout, 1962;Scharloo, 1964;Barnes, 1968). All of these studies assumed or were carried out in a constant environment.…”