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人类社会或群体的性比R,是指该社会或群体中男性个体数相对于女性个体数的比值。例如一个由54名男性和50名女性成员组成的群体,其性比R为1.08。现代人类社会人口结构的大量统计资料表明,在无大规模战争的常规情况下,其性比接近于1,即男女个体数大致相等。例如1984年我国人口普查表明全国人口的性比是1.063。正常性比数值接近于1是由人类繁衍的生理机制所决定,因为生殖细胞是由身体细胞减数分裂所形成,这就决定了男性的X精子与Y精子数严格相等。而在自然受孕过程中这两种精于被卵子接纳的概率并没有表现出显著的倾向性。
The sex ratio R of a human society or group refers to the ratio of the number of male individuals to the number of female individuals in that society or group. For example, a group of 54 men and 50 women has a sex ratio R of 1.08. The mass statistical data on the demographic structure of the modern human society show that in the conventional case without a large-scale war, the sex ratio is close to 1, that is, the number of men and women is roughly equal. For example, the 1984 national census showed that the sex ratio of the entire country was 1.063. Normality is closer to 1 than the value of the physiological mechanism of human reproduction, because germ cells are formed by body cells meiosis, which determines the number of male X sperm and Y strictly equal to the number of sperm. In the process of natural conception of these two kinds of skilled in the probability of being accepted by the egg did not show significant propensity.