Interesting point. Probably there are many historical case studies of populations with unbalanced sex-ratios. There are many reasons for it to go out of balance

Interesting point. Probably there are many historical case studies of populations with unbalanced sex-ratios. There are many reasons for it to go out of balance. Recent/currently China and Russia are examples. According to wikipedia; the ratio of boys to girls is 1.3:1 in some rural areas in China.