xia@cc.helsinki.fi (11/11/90)
The theory of adaptive sex ratio states that natural selection should favour parents that can adjust their offspring sex ratio according to prospective reproductive success of sons and daughters. I have some good data on adaptive sex ratio adjustment, which were collected in a Chinese rural vilage in 1981-1982. The main findings are: 1. Son's social status is positively correlated with his father's social status (highly significant). This is true for boys in primary school, high school and thereafter. 2. Daughter's social status after marriage is only weakly correlated with her father's social status. 3. Number of offspring one has is positively correlated with one's social status. (Therefore it is beneficial for a couple of high social status to have sons.) 4. Social status increases with age up to 55 years old (only for men), but men usually stop breeding around 45 years of age. (Because a new family is usually of low social status, it should produce daughters.) 5. The prediction that daughters will be produced before sons is strongly supported. The result is far more clear-cut than any data I collected on animal populations. But how could sex ratio adjustment possible in humans? I asked several medical experts. They told me that they have been trying to seperate X-sperms from Y-sperms with very limited success. How could social status affect a woman's reproductive tract to select the right sperm for her offspring? This question has intimidated me for many years and I still do not have courage to submit the above result for publication.