It is not often that you can be sure about the future. If you explode a bomb you can be sure there will be some destruction. This is because we are following the routine of the past. A doctor who treats a streptococcal infection with penicillin can be reasonably sure that it will effect a cure. Again, this is repeating a routine that has worked in the past.
In China there is said to be a deficit of 100 million women. This is the result of the ‘one child’ policy. Baby girls are not much valued because they are not so helpful in the fields or in your business. Girls get married and then look after the aging parents of their husbands. So who is going to look after you when you get old? So, somehow, the girl babies disappear. The result is a deficit of 100 million women - and even wife kidnapping.
Each family is allowed to have one boy and must then have more children. This is the ‘one boy’ policy. The result is equal boys and girls. At the moment of conception there is an equal chance of the embryo being a boy or a girl. Since no one is being killed, this equal chance continues. On average each family has two children. This is less than is required for population replacement, which needs about 2.3 children. So there is a declining population of equal boys and girls and everyone gets the chance to have a boy. No babies are ‘lost’ or killed.