“…However, in these investigations the other sources of variation had not been explicitly considered, in particular the maternal tendency to generate offspring of one sex, which may be confounded with the positive interaction between sexes in consecutive births. In our analysis, in which Lexian variation between the mothers was considered, the influence of the sex of a birth on the following one, formalized as a non-stationary Markov process, showed a non-significant effect and, when excluded, the reduced (1978), while in humans a negative and significant trend was found by Novitski and Sandler (1956), Novitski and Kimball (1958), Pickles et al (1982) and Crouchley and Pickles (1984).…”