Chinese zodiac results in distortion of sex ratio.

The sex ratio [male/female (M/F)], which is defined as the ratio of males to females in a population, is assumed to be close to 1:1. However, at birth, the sex ratio of males to females is approximately 105:100. In some countries, and especially in ethnic Chinese societies, a significant change and distortion of the sex ratio at birth have been reported. Dr. Grech has published an article in this issue addressing this topic in Hong Kong, and showed that the birth rate and sex ratio were both influenced by the Chinese zodiac (Shengxiao: a 12-year Chinese cycle with each year given an animal's name, from rat to pig). The main findings of Dr. Grech's study were: (1) the sex ratio at birth in Hong Kong showed peaks in Dragon years, including 1975e6, 1988, and 2000; (2) the sex ratio remained stable overall, within a relatively narrow range, except for a rise commencing in 2004; and (3) there was a slow decline in the total number of births that reversed in 2004. Dr. Grech suggested that the M/F ratio follows a Ushaped regression on cycle days of insemination; that is to say, female conceptions result from conceptions around ovulation, and male conceptions occur more frequently at the beginning and end of the menstrual cycle. In addition, families in Hong Kong attempting to have children during Dragon years may have increased coital rates, inadvertently skewing the sex ratio in favor of an excess of males. Although the explanation may be reasonable, some are not clear. The first question is with regard to the frequency of coitus rates being related to the high birth rate. In some countries, this may be true, because there is an absence of effective contraception methods. However, many contraception methods are relatively advanced and highly accessible in modern societies, including Hong Kong, so it is not credible that higher coitus rates will result in higher pregnancy rates. In addition, conception is influenced by many nonbiological factors, such as economic, social, cultural, and ethical factors. For example, in Taiwan, the number of newborns has dramatically and progressively declined in recent years. No one believes that the decline in the number of newborns is secondary to a decreased coitus rate. Therefore, the change in birth rates cannot be explained simply by coitus rates. Although it has been scientifically demonstrated that lunar cycles might have an important effect on several biological events, controversy exists regarding the lunar influence on