The World Population Prospects: The Revision , published by the UN Department of Economic and Social Affairs, provides a comprehensive review of global demographic trends and prospects for the future. The information is essential to guide policies aimed at achieving the new Sustainable Development Goals.
The new projections include some notable findings at the country level. China with 1. In roughly seven years, or around , the population of India is expected to surpass that of China. Among the ten largest countries worldwide, Nigeria is growing the most rapidly. The group of 47 least developed countries LDCs continues to have a relatively high level of fertility, which stood at 4. As a result, the population of these countries has been growing rapidly, at around 2.
Similarly, Africa continues to experience high rates of population growth. Between and , the populations of 26 African countries are projected to expand to at least double their current size. In recent years, fertility has declined in nearly all regions of the world. Even in Africa, where fertility levels are the highest of any region, total fertility has fallen from 5. Europe has been an exception to this trend in recent years, with total fertility increasing from 1. More and more countries now have fertility rates below the level required for the replacement of successive generations roughly 2.
Additional youth-related indicators include: percent of demand for family planning satisfied by modern methods for married women ages ; percent of youth living with HIV in Sub-Saharan Africa, by gender; percent of secondary students, ages , who use alcohol or tobacco products, or are overweight or obese, by gender; and percent of youth using a computer or the internet. The SDG Update compiles the news, commentary and upcoming events that are published on the SDG Knowledge Hub each day, delivering information on the implementation of the Agenda for Sustainable Development to your inbox.
Newsletter The SDG Update compiles the news, commentary and upcoming events that are published on the SDG Knowledge Hub each day, delivering information on the implementation of the Agenda for Sustainable Development to your inbox. In the two charts here we see two perspectives: firstly a global map of the sex ratio at five years old. Just as with the sex ratio at birth, we see the highest ratios in several Asian countries where the share of boys is higher than we would expect.
In China, there is close to boys per girls at age five; in India, there are more than boys per girls. Secondly we see a scatterplot comparison of the sex ratio at birth on the y-axis versus the ratio at five years old on the x-axis. The grey line here represents parity: a country which lies along this line has the same ratio at five years old as it does for birth.
As we see, most countries lie above this line: this means the sex ratio for newborns is higher than for 5-year-olds. In other words, the male-bias tends to weaken through the first years of childhood.
Why is this the case? As we explore in the next section of this entry: across most countries infant and child mortality rates are higher for boys than for girls.
This means fewer boys survive the first few years of life. For most countries this results in a decline in the sex ratio. Overall we see that despite higher child mortality in boys, the sex ratio at age five in the majority of countries is over this means boys still outnumber girls in childhood.
From life expectancy to mental health ; substance use to cancer rates ; there are important differences in health outcomes between the sexes. Here we focus on the youngest, asking, why do young boys die more often than girls? Child mortality measures the share of newborns who die before reaching their 5th birthday. In the chart below we see the comparison of child mortality by sex. Here, the mortality rate for boys is shown on the y-axis, and the mortality rate for girls on the x-axis. The grey line running diagonally across the chart marks where the mortality rate for both sexes is equal.
In countries which lie above the grey line, the rate for boys is higher than for girls. This is also true for infant mortality , which is the share of newborns who die within their 1st year of life. We study why India and Tonga are outliers here. Over the past half-century in particular, child mortality has been falling rapidly across the world. This has been true for boys and girls alike. It has been known for a long time that the mortality of boys is higher. Why is it the case that boys die more often than girls?
In this chart we see global mortality rates in infants across different causes in Just like the charts above, causes which lie above the grey line are more common in boys.
The chart shows that for all major causes of death, mortality is higher in boys. The sex differences in the causes of infant deaths were already documented almost a century ago: in an impressive paper published in , Bawkin explores the mortality sex ratio of specific diseases from countries across the world.
But overall, infant boys are more likely to die in childhood than girls. Boys are more vulnerable in two key ways: they are at higher risk of birth complications, and infectious disease. We explore the possible reasons for this below. From comparison of mortality rates in infant boys and girls, it becomes clear that boys are at higher risk of complications in the first few days of life: preterm births, asphyxia, birth defects and heart anomalies.
But why? First of all, boys are more likely to be born prematurely : the share of boys born before full-term pregnancy is higher than for girls. Boys tend to have a higher birthweight than girls — which can increase the risk of waiting to term to deliver — meaning that more boys are induced before the end of the pregnancy term.
The fact that preterm births are more common for boys contributes to this. Although boys are, on average, heavier than girls at birth, they are less physiologically mature at birth. This means they are at higher risk of having delayed physiological function such as lung function and adverse neurological outcomes.
The reason for this difference has been an important question for decades — the answer is still not clear. But there are some leading hypotheses: surfactant production for lung function has been observed earlier in female fetuses, leading to improved airway flow in the lungs; estrogen has been shown to affect lung development positively in females; males, on average, have a higher birthweight meaning they may trade-off increased size for functional development; and the uterus may be less hospitable to male fetuses — the introduction of a Y chromosome in females can create and immunoreactive response to the central nervous system.
This, combined with a higher risk of premature birth may explain why boys have higher rates of asphyxia, respiratory infections and birth defects.
Boys are also at higher risk of infectious diseases such as syphilis, malaria , respiratory infections, tetanus and diarrheal diseases. This is more generally true for a broad range of infections, spanning person-to-person, vector-borne, blood-borne, and food and water borne diseases. We see this clearly when we compare mortality rates for boys and girls in the earlier chart. But why are boys more susceptible to infection? Overall, boys have weaker immune systems. There are two key hypotheses for why.
The Y-chromosome in boys increases their vulnerability. Biologically, males and females are differentiated by chromosomes: females have two X chromosomes XX and males one X and one Y chromosome XY. Having two X chromosomes means that the newborn has a stronger immune system because X chromosomes contain a larger number of immune-related genes.
This makes males more vulnerable to many infectious diseases. They are also more susceptible to specific genetic diseases where the defective genes are carried on either the X or Y chromosomes; this is because boys have only one X chromosome so a single recessive gene on that X chromosome results in the disease.
But the stronger immune response of females comes with a cost. Sex hormones may be another key reason for weaker immune systems in males.
Males have much higher amounts of testosterone which seem to inhibit two major parts of the immune system — B and T-lymphocytes. Estrogen, on the other hand, acts as an effective regulator of this.
Overall, male hormones weaken the immune system relative to females. This is not restricted to childhood: the female advantage carries into adulthood. More specifically, differences in maturity, sex chromosomes, and hormones. In circumstances where both sexes are treated equally, we would therefore expect infant and child mortality rates to be slightly higher for boys. The sex ratio — the number of males relative to females — at birth and in childhood are male-biased in almost every country.
In this chart we see the sex ratio — measured as the number of males per females — at different ages through adolescence and adulthood. In the global average for adolescents and young adults we see the result of both the male-bias in birth ratios and the large impact of populous countries such as China and India with very skewed sex ratios: At age 15 and 20, males outnumber females by to But as we move through adulthood we see that this ratio is lower and lower.
For year-olds the ratio is close to 1-to-1; for year-olds there are only 89 males per females; and in the very oldest age bracket year-olds there are only 25 men per women. You will see that for some countries this decline in the sex ratio with age is even more extreme: in Russia, for example, by age 50 there are only 88 males per females; by 70 years old there are almost twice as many women as men.
In every country in the world women tend to live longer than men. On average, women live longer than men — this is true for every country in the world. This fact plays an important role in how the sex ratio changes with age through adulthood. Today, and at several points historically, the sex ratio at birth in some countries is too skewed to be explained by biological differences alone.
In a recent study Chao et. Most of these countries are in Asia. Is there a biological or environmental difference, or is it the result of discrimination? The reason for this skew in sex ratio has been previously challenged. One of the leading hypotheses was put forward by economist Emily Oster. The authors concluded that hepatitis B rates could not explain the skewed sex ratio in China.
Other studies — such as that by Lin and Luoh in Taiwan — have also found minimal to no effect of hepatitis B on the sex ratio. Sex-selective abortions and discrimination against girls After the hepatitis B hypothesis was debunked, no clear evidence of a biological factor in such skewed sex ratios has emerged.
But the natural variability of the sex ratio is too small to explain the high ratios in some countries. The evidence for sex-selective abortion and discrimination against girls is now strong across several countries. Not only does the increase in sex ratios coincide with the availability of prenatal sex determination technologies, there is also clear evidence from studies investigating the use and promotion of such methods.
In India, for example, prenatal diagnosis PD became available in the s, shortly after legalization of medical abortion in Results from some of the earliest studies on abortions following the availability of prenatal sex determination are striking. Results from another six hospitals in the city found 7, of the 8, aborted fetuses in were girls. The evidence that highly skewed sex ratios at birth have been largely the result of gender discrimination and selective abortions has been well-established across several countries.
We discuss the reasons for this discrimination here. There are some additional hypotheses as to why the sex ratio at birth is skewed in some countries. Sex discrimination can occur prenatally in the form of sex-selective abortions, as we discuss here or postnatally when it can lead to the death of a child in the very worst cases.
The death of a child due to sex discrimination can be brought about in a deliberate killing of an infant infanticide or can be caused by neglect or poor and unequal treatment. Over time, prenatal discrimination has increased as both abortions and sex determination technologies have become more readily available. Nonetheless, postnatal discrimination still occurs and has a long history.
Infanticide or infant homicide — the deliberate killing of newborns and infants — has a long history. Rather than being an exception, then, it has been the rule. And humans are not alone. From birds to rodents; fish to mammals; we find evidence of infanticide across the animal kingdom. There are some common misconceptions today surrounding the practice of infanticide. A number of researchers have studied the demographic, health and cultural profiles of prehistoric societies.
In rare cases they can use indirect evidence of the fossil record; but many rely on modern hunter-gatherer societies today.
Estimates for infanticide in prehistoric societies are very high. They did this using census and interviews gathered over a seven year period. Infant mortality rates in the past were very high — most studies suggest around a quarter of newborns did not survive the first year of life. They also found large sex differences: infanticide rates were four times higher for girls than boys. Other studies of modern hunter-gatherer societies analysed the sex ratio of infants to estimate the prevalence of infanticide.
Very skewed sex ratio of infants is suggestive of select infanticide. In studying 86 hunter-gatherer bands across North America, South America, Africa, Asia and Australia, researchers found high levels of female infanticide across 77 of them.
The practice of infanticide was not just common in prehistoric societies, but was also very common in many — but not all — ancient cultures. Sometimes here is no clear gender discrimination, and it occurs for both sexes. There is of course significant evidence of female-selective infanticide throughout history: we see that in the sex ratio of many hunter-gatherer societies above through to skewed ratios in Medieval England.
Even today, cases on infanticide still exist, despite being outlawed in most countries. This remains reported across countries with a strong son preference: India and China are the most documented examples. Infanticide is the most direct case of postnatal sex selection. More often overlooked is the excess mortality which results from neglect and unequal treatment of girls.
Poor treatment of girls results in increased mortality in childhood In almost every country young boys are more likely to die in childhood than girls — as we explore here , there are several biological reasons for is.
But this is not true in a few counties — India is one notable example today. There, girls die more often than boys. When we compare infant under one year old and child under-5s mortality rates between boys and girls in India we see that the difference is bigger for the older age group.
While infant mortality rates are approximately the same, the child mortality rate for girls is higher.
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