In the wild, an imbalance between genders sometimes results when conditions favor one over the other. For instance, in species where the male is larger and requires more food, in times of scarcity more female offspring will be born. Usually the imbalance corrects itself in a few generations. The scarcity of one gender creates a breeding advantage for offspring of that gender, thus exerting countervailing selection pressure.

Here we have a societal more that expresses a preference for male offspring combined with the ability to select gender via selective abortion or, in some cases, infanticide. Left to its own devices, we would expect in a few generations to see the advantages of having daughters become conspicuous enough to exert pressure in the other direction.

The key question is if this particular more -- preference for male offspring -- is susceptible to reality. When having a daughter is far more likely to result in your line being carried on than having a son, one would expect values to shift away from preference for males. However, there is reason to believe that even now that widespread preference for male offspring among the lower classes is an example of adoption of an upper-class belief (Having sons is advantageous because it keeps the fortune within the family) by a class that receives no benefit from this strategy. For the poor, daughters are far more likely to marry into a higher class, so logically that should be the preference. In the past it generally would have been, because most societies were quite comfortable with having one set of values for the rich and another for the poor.

Now what we seem to be seeing is billions of poor people attempting to employ the breeding strategies of the rich and, in doing so, courting disaster.