Isn't hackernews meant to be politics free? Would be great if there was at least one place we didn't need to read these tiresome comments from people who can't comprehend that others have different value systems.
That's why we would all be sleeping easier in our bed if the Chinese would just accept externla help from the USA/WHO/anyone. So far as I understand, there are currently no external observers. There are no reliable sources. Daily Mail is currently no more or less reliable than any other source currently.
To be fair, the set of conditions and circumstances cropped up in Singapore as well. One could be forgiven for thinking that if the circusmtances could be engineered then, they could be engineered now.
Intelligence and fertility are known as complex traits. The fact they are complex doesn't mean they are not acted on by genetics: they are just highly polygenic. Almost all attempts to measure the heritability of intelligence have reached estimates between 50 and 80%.
If you accept the heritability for age at first birth has not been measured wrong, then the hypothesis put forth by this paper will come about.
Perhaps I over stated the case by saying inevitable. It's quite feasible that the consequences of highly fertile people overbreeding will be a reduction in civilizational complexity, which will lowerthe total population.
What you should understand is: most geneticists wouldn't have had the balls to write this even though it's obvious to them. Someone did have the courage to write it. Now wrap your head around what they wrote.
“First Law: All human behavioural traits are heritable.
Second Law: The effect of being raised in the same family is smaller than the effect of the genes.
Third Law: A substantial portion of the variation in complex human behavioural traits is not accounted for by the effects of genes or families.”
Beyond that though, the genetics of human fertility is pretty well understood. Here's a (now fairly old: from 2016) GWAS study on human reproductive behaviour: https://www.ncbi.nlm.nih.gov/pubmed/27798627
They show genetic correlations between reproductive traits and other behavioural traits in Figure 3. You might find it helps you develop an intuitive understanding. Happy to answer questions if you have any.
This study (https://www.pnas.org/content/114/5/E727) measured the speed at which selection against cognitive ability is occuring in the Icelandic population (they measured this genotypically rather than phenotypically). The rate at which it occurs is meaningful on the scale of our lifespans. Same is probably true for fertility rates, but as fertility is being selected for directly (rather than the indirect effect on cognitive ability) it's probably even more rapid.
Then this study more directly measured fertility's rate of evolution: https://www.pnas.org/content/115/1/151. They used UK Biobank data (genetic data from 157,807 female and 115,902 male unrelated samples). They found the 'Age at First Birth' is the most strongly selected trait in the British population. So in the future we can look forward to a world filled with teenage mums.
That this is not obvious to everyone is just a testiment to how little people understand about evolution.