A closer look
Left to nature alone, the population on earth would be give or take 50% men and 50% women, according to what's become known as Fisher’s Principle. The fact that women generally live longer (PDF, page 259) is compensated by the fact of more boys being born than girls (107 boys per 100 girls in 2013).
In 1961, the earliest year the World Bank provides data for, the world was within 0.09 percentage points of a perfectly equal distribution. Ever since, the gap has widened; now men outnumber women on the planet by almost 60 million.
The male surplus is the result of various, partly diverging trends. In 2013, female population in individual countries ranged from 23 to 55%. Some countries have seen a change of as much as 19 percentage points over the past five decades, others have had notable ups or downs within relatively short periods.
(The data, provided by the World Bank, based on the United Nations Population Division's World Population Prospects, use interpolation between five-year periods to obtain annual data. Events that caused a significant change within a relatively short time might thus be reflected in the data with a delay and appear more linear than they have in fact been.)
The missing girls in China and India
In 2013, men outnumbered women on the planet by roughly 58 million, according to the World Bank. What makes this possible, even though a majority of countries have more women than men, is the fact that the most populous countries in the world are also highly imbalanced: China has nearly 50 million more men than women, India 43 million, accounting for 76% of the male surplus worldwide.
Gender imbalance starts at birth: Both China and India are infamous forwidespread gender selective abortions and female infanticide. Both countries have birth sex ratios that are well off the worldwide average. In 2013, China saw 1.11 boys born per girl, India 1.12, as compared to 1.07 worldwide. The availability of affordable prenatal diagnostic techniques has only accentuated the trend, which means the gender gap in the general population is bound to widen in the coming years, as more balanced older generations pass away. In an attempt to break the trend, India has legally banned sex determination before birth in 1994, legislation that has, however, been criticized as ineffective. In 2013, China loosened its one-child policy, one of the main drivers of gendercide.
Two other countries in the region with a similar population structure, Pakistan and Bangladesh, have seen significant changes over the past decades. While Pakistan, the most unbalanced of the four in 1961, has improved and moved past China and India to greater equity, Bangladesh is approaching a balanced population in this century. This can be attributed to a shift in culture—labelled “the rise of the daughter-in-law” phenomenon—from one that strongly preferred sons to one that values boys and girls equally.
Migrant workers on the Arabian Peninsula
The most gender imbalanced states in 2013 were all found on the Arabian Peninsula, Qatar being the most extreme. Less than one quarter of all people who lived in Qatar in 2013 were women. Those countries have attracted a lot of migrant workers for male-dominated industries, especially after oil prices started rising in the 1970s and the industry grew. Millions of men, mostly from South Asia, came to work on the Arabian Peninsula, but weren't allowed to bring their spouses and children with them, thus throwing gender ratios off balance.
