Abstract:

Based on demographic data from 1427 to 1971 from a Chinese (Hans)family tree and circular distribution analysis, the authors show that the highest male birth rate was 16.04 % from 21:00 to 23:00 in a 24-hour day, which was 3.89 times hig her compared with the lowest 4.12 % from 15:0 0 to 17:00.For girls, the highest birth rate was 20.09 % from 23:00 to 01:00 and 5.46 times higher than the lowest 3.68 % from 19:0 0 to 21:00.The mean birth peaks of boys and girls were at 22:4 9 and 23:25, respectively,and the difference w as not significant (P>0.05).The mean time for both boys and girls was at 23:11.Birth rates at night (17:00 ～ 05:00) were 12 % and 11 % higher than in daytime (05:00 ～ 17:00)for boys and girls, respectively, and both of the differences were highly significant (P < 0.01).The birth rates of boys were 42.65 %in Yang hours and 57.35 %in Yin hours, with a highly significant difference.The female births were 46.78 % in Yang and 53.22 % in Yin hours, respectively, with a nearly sig nificant difference(P = 0.10).The peak bi rth hours of boys in both ancient (1427 ～ 1840)and modern (1841 ～ 1971)times were 21:0 0 ～ 23:00, w hereas the peak hours of girls were 23:0 0 ～ 01:00 in these times.The birth time of boys during the day seems to be delayed as the age of mothers increase, but the linearregression is not significant.

Key words: birth rate, ci rcadian rhythm, circular distribution, Chinese family tree, historical ecology