The comment about K/r is (IMHO) the only one who seems to be on track, but it fails to mention exactly how we should apply it to our case.

My present line of reasoning goes along the lines: in contemporary affluent societies human beings are competing not with environmental factors but with other humans, whereas in more traditional societies the weight of this intra-species competition was less relevant.

In any case, i think the phenomenon underlines how much what we think as “material wealth” is actually not very relevant to survival but exclusively as status signaling.

My theory for the demographic transition is here. In short, humans have a weak innate drive to reproduce, but strong innate drives to have sex and gain social status. In the past reproduction was largely mediated through these drives. Prior to female educational and economic integration, the female status drive was adaptive; it resulted in higher reproductive success — i.e more surviving offspring — because women would seek to elevate their status through the one channel available: by acquiring high status mates. In turn this made high reproductive success itself a desirable symbol of social status, since higher status women had more children.

But post-women’s liberation, status drive would have the opposite effect. Now status motivated women have to marry well and participate in the workforce to remain competitive with other women in the adult status arena. The time and expenses necessary for raising children are instead invested in education, career-building, and conspicuous consumption. In turn this makes low reproductive success a symbol of social status, since higher status have fewer children.

The link between demographic transitioning and status drive are supported by a number of newer papers in the economics literature.

For example, one recent study from Brazil suggests that status imitation drove their demographic transition. As soon as different regions acquired access to Soap Operas (1960-2000) about small, middle-class Brazilian families, local birth rates would drop dramatically to the levels featured in the TV shows (from 6.3 to 2.3 children), and parents would name their children after the characters in those shows.

A similar effect on fertility followed cable television introduction in India.

In other words, as soon as women see higher class women adopt low fertility behaviors, they rapidly follow suit.

It is my never humble opinion that our immune systems have adapted, but not for the better.

An obsession with germ killing (freakin’ hand sanitizers and antibacterials EVERYWHERE) leaves us less exposure, thereby weakening the immune response.

It doesn’t get enough exercise.

And the germs have incredible adaptive immune systems – witness the ubiquitous “antibiotic resistant” bacteria and ever changing viruses (AIDS, for example).

I thought this was all pretty well known? The Demographic Transition and all that. Death rates fall as a result of increased wealth and stability while the natal-norms that prevailed in a period of high infant mortality continue on for a while before people adjust. Old preferences of having a lot of pregnancies in order to have several surviving children continue into an age where many more infants make it to adulthood than before. Birth rates only adjust after a long and variable lag where people pick up on the drawbacks of large families and adjust their natal-norms to reflect the new environment.