The selection pressure is real, but it is not the only force in play. Economic pressure is acting too, and it is against raising children; they are expensive to raise to adulthood, and you cannot derive any material benefit from them. It seems to me that, in this case, the economics have much greater force than the genetics. Whatever disposition toward childbearing you inherit from your parents, whether genetic or ideological, is a small thing compared to whether circumstances make providing for them practical.
In general, when dealing with a complex system, it is not enough to know that a single force is acting on it. You need to understand all the forces, and how strong they are and how they behave. All too often, this is the case with selection pressure arguments -- supposing that the force in question is the only one in play, without any regard for whether it has the power to do the job expected of it.
I find that the best course of action is usually to look at the actual data, and see how the system really is behaving, apart from theory. Nontrivial systems very rarely meet naive expectations.
True as that may be, people are not acting the way that would lead you to expect.
World population appears to be on a logistic curve --
http://en.wikipedia.org/wiki/Logistic_function
http://en.wikipedia.org/wiki/File:World-Population-1800-2100...
-- and birth rates for a lot of the world are close to or below replacement.
http://en.wikipedia.org/wiki/Fertility_rate
The selection pressure is real, but it is not the only force in play. Economic pressure is acting too, and it is against raising children; they are expensive to raise to adulthood, and you cannot derive any material benefit from them. It seems to me that, in this case, the economics have much greater force than the genetics. Whatever disposition toward childbearing you inherit from your parents, whether genetic or ideological, is a small thing compared to whether circumstances make providing for them practical.
In general, when dealing with a complex system, it is not enough to know that a single force is acting on it. You need to understand all the forces, and how strong they are and how they behave. All too often, this is the case with selection pressure arguments -- supposing that the force in question is the only one in play, without any regard for whether it has the power to do the job expected of it.
I find that the best course of action is usually to look at the actual data, and see how the system really is behaving, apart from theory. Nontrivial systems very rarely meet naive expectations.