Well, you may or may not have said anything about fetuses. You could have edited it away as well.
My point was that people are making assumptions about demographic changes here that could be explained by non "murdering your firstborn" means. Since we're basically neglecting an entire potential subfield of relevant research here, then we can't in fact assume anything about why it's happening (or alternatively the scale of things), without proper evidence.
In fact, it's probably explainable by racism that we automatically assume it's because evildoers when it's another race, but when it's our own race we go "well who's to say why it's happening?".
e.g. an extremely wealthy nation such as Lichtenstein is a great barometer here, since it's highly unlikely they're bashing girls to death at birth or secretly aborting 20% of fetuses, when they don't even have abortion clinics there. And their birth ratio is far more skewed than China!
Wait, there it is.
Well a quick google brings up this:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0023792
Evolutionary theory posits that resource availability and parental investment ability could signal offspring sex selection, in order to maximize reproductive returns. Non-human studies have provided evidence for this phenomenon, and maternal condition around the time of conception has been identified as most important factor that influence offspring sex selection. However, studies on humans have reported inconsistent results, mostly due to use of disparate measures as indicators of maternal condition. In the present study, the cross-cultural differences in human natal sex ratio were analyzed with respect to indirect measures of condition namely, life expectancy and mortality rate. Multiple regression modeling suggested that mortality rates have distinct predictive power independent of cross-cultural differences in fertility, wealth and latitude that were earlier shown to predict sex ratio at birth. These findings suggest that sex ratio variation in humans may relate to differences in parental and environmental conditions.
Trivers and Willard predicted that, in polygynous mating systems, mothers in good condition could increase reproductive success by biasing investment in sons. Superior quality sons can leave many more offspring than daughters can. Hence, where the fitness gains of offspring quality are sex specific, a female with ability to produce high-quality offspring could be expected to produce more sons and vice-versa. Empirical evidence for biased offspring sex ratios gathered from many taxa support this theory
...
Meta-analysis of non-human studies has suggested that sex ratio adjustments are most likely to occur around the time of conception. This adjustment was strongly correlated with maternal condition around conception, such that mothers in good condition during this period produced more sons. Similar findings have been reported in humans when maternal condition was considered in relation to sex ratio adjustment
Average national sex ratio at birth (SRB) in humans is slightly male biased (105 males per 100 males), with remarkable deviation for some countries. Systematic deviations from this ratio occurs in conditions such as economic and natural catastrophes, war, chronic stress, etc. Demographic factors like ethnicity, parental age, mother's weight, birth-order, smoking, certain disease conditions, certain professions, exposure to environmental toxins, seasonality of birth, etc are also linked to sex ratio adjustments. These studies have shown that higher birth-order, older parental age, low or high maternal weight, exposure to toxins and stressful events lower the chances of male births
So basically, things seen as "unhealthy" e.g. the mother being old or too fat or too thin, or malnourished or stressed or sick from toxins, all reduce the chance of a male birth. The interesting part here is that all the observed "negative" things about the mother's condition seem to reduce the chance of having a boy: not one of them increases the chance.
The possibility that the human natal sex ratio may relate to variation of life-expectancy and mortality rates has received surprisingly little attention from researchers. Indeed, only one study has investigated the relation between life-expectancy and natal sex ratio in a small sample of contemporary British women, finding that women who believed they had longer to live were more likely to have a male birth than women who thought they would live shorter
I'll make the suggestion that this field of research has had "surprisingly little attention" from researchers because it's not politically correct to suggest that people would have more male children if you improve their standard of living, regardless of how scientifically accurate it is. We have no issue however observing gender variation in animals, so this has in fact been observed in dozens of other species.
However this also opens up some interesting perspectives on deliberate sex selection in impoverished nations. If the theory is correct, then impoverished people have more girls, but the problem is that we enforce monogamy, not polygyny, which is what innate sex-selection is geared for. Hence, impoverished nations would have excess girls by that measure, and would need some boy-baby bias just to maintain equal sex ratios. However, when standards of living then rise, that cultural sex-selectivity is now out of whack with the sex ratios, leading to excess male births.
That's exactly what we see in India and China - excess male population is blamed on generations of sex-selectivity. However, India and China didn't have a "girl shortage" until very recently, but the practices of pro-male sex-selection go back centuries. The data on poverty and innate gender selection can explain this issue.
EDIT: Note that the nation with the most skewed birth ratio in favor of boys is Lichtenstein, with 1.26 boys born per 1.0 girls. Some people are claiming that Lichtenstein people are seriously aborting the "missing" girls. However ... abortions aren't even legal in Lichtenstein, and it's hard to believe that literally 1 in 5 baby girls are aborted in the entire nation in the world's richest nation per capita, when you'd have to either do a backyard abortion or travel to another nation to get it done, and yet nobody is noticing this happening. Note that Lichtenstein has the highest GDP per capita of any nation in the world, along with an extreme level of income equality, so it might be an outlier of what happens when you have a large group of people who all have good nutrition and standard of living etc. A very low ratio of female births.
But it is nowhere near 20% actually.
Total amount of live born children in Lichteinstein in 2011 was 395. Lichtenstein is tiny.
In the same year the ration boys/girls was 1.26/1 That means that out of 2.26 children 1.26 were boys and 1 was girl.
1.26/2.26=0,558
1/2.26=0,442
Multiplied by the number of children born:
0.558*395=220
0.442*395=175
So, the difference between girls and boys was only 45 children.
If girls were added to have equal amount, total children would be 395+45=440
45/440=0,102
Only about 10% of fetuses would have to be aborted without a clinic. 20% of girl ones though.
Also in the same post you said that there does not seem to be anything increasing the chance of boy being born and that it is increased by something in Lichtenstein.
But The Principality of Lichtenstein is so small, that most of statistics there are not representative.
