[HideousKojima]

>The number of 2.1 as the replacement rate is based on some estimate of human labor output.

Replacement rate has to do with keeping the actual population number stable, not labor output whatsoever. It's 2.1 instead of just 2 because of infertility, child mortality (and mortality before reproducing generally), etc.

It has literally nothing to do with robots or efficient labor. Any TFR lower than ~2.1 will result in the total population shrinking.

[ActorNightly]

So are you saying its based on genetics? I always thought that it was related to economics of keeping things like supply chains for food going and other factors.

[HideousKojima]

Not even genetics, just simple population numbers. It takes 2 humans to make a new human. If each female human on earth isn't making, on average, 2 new humans (plus the .1 extra to make up for infertility and mortality) then the population of the world will shrink. Simple as.

[kbelder]

Well, in a sense all babies are a result of human labor output ;)