It arises from the observation that even small changes can alter the timing and circumstances of child conception, leading to entirely different individuals coming into existence, similarly to the butterfly effect in chaos theory.
In the depletion strategy, current generations have a slightly higher quality of life, but unchecked use of natural resources eventually leads to depletion, significantly degrading the welfare of future generations.
[4] A solution to the problem is to adopt impersonal views, theories that don't rely on the notion of personal identity, such as utilitarianism.
But impersonal views lead to what Parfit calls the "repugnant conclusion", the idea that "For any perfectly equal population with very high positive welfare, there is a population with very low positive welfare which is better, other things being equal.
"[3] Some philosophers consider, however, that almost all credible theories of population ethics imply some form of the repugnant conclusion anyway.