Human sex ratio

Human sex ratio

Ask a question about 'Human sex ratio'
Start a new discussion about 'Human sex ratio'
Answer questions from other users
Full Discussion Forum
In anthropology
Anthropology is the study of humanity. It has origins in the humanities, the natural sciences, and the social sciences. The term "anthropology" is from the Greek anthrōpos , "man", understood to mean mankind or humanity, and -logia , "discourse" or "study", and was first used in 1501 by German...

 and demography
Demography is the statistical study of human population. It can be a very general science that can be applied to any kind of dynamic human population, that is, one that changes over time or space...

, the human sex ratio is the sex ratio
Sex ratio
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....

 for Homo sapiens
Humans are the only living species in the Homo genus...

(i.e., the ratio
In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

 of male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...

s to female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...

s in a population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

). Like most sexual species, the sex ratio is approximately 1:1. In humans the secondary sex ratio (i.e., at birth) is commonly assumed to be 105 boy
A boy is a young male human , as contrasted to its female counterpart, girl, or an adult male, a man.The term "boy" is primarily used to indicate biological sex distinctions, cultural gender role distinctions or both...

s to 100 girl
A girl is any female human from birth through childhood and adolescence to attainment of adulthood. The term may also be used to mean a young woman.-Etymology:...

s, an assumption that is a subject of debate in the scientific community. The sex ratio for the entire world population
World population
The world population is the total number of living humans on the planet Earth. As of today, it is estimated to be  billion by the United States Census Bureau...

 is 101 males to 100 females

Gender imbalance may arise as a consequence of various factors ranging from natural factors and war casualties to intentional gender control and deliberate gendercide
Gendercide is a neologism that refers to the systematic killing of members of a specific sex.-Gendercide:Gendercide is gender-selective mass killing. The term was first used by Mary Anne Warren in her 1985 book, Gendercide: The Implications of Sex Selection...


More data are available for humans than for any other species, and the human sex ratio is more studied than that of any other species, but interpreting these statistics can be difficult.

Human sex ratios, either at birth or in the population as a whole, might be quoted in any of four ways: the ratio of males to females, the ratio of females to males, the proportion of males, or the proportion of females. If there are 108,000 males and 100,000 females, the ratio would, respectively, be quoted as 1.080, 0.926, 0.519 or 0.481. Sex ratio in scientific literature is often expressed as the proportion of males. In contrast, sex ratio quoted in this article is the ratio of males to females, unless specified otherwise.

Natural ratio

In a study around 2002, the natural sex ratio at birth was estimated to be close to 1.06 males/female. In most populations, adult males tend to have higher death rates than adult females of the same age (even after allowing for causes specific to females such as breast cancer and death in childbirth), both due to natural causes such as heart attacks and strokes, which account for by far the majority of deaths and also to violent causes, such as homicide and warfare (for example, in the USA as of 2006, an adult non-elderly male is 3 to 6 times more likely to become a victim of a homicide and 2.5 to 3.5 times more likely to die in an accident than a female of the same age), resulting in higher life expectancy
Life expectancy
Life expectancy is the expected number of years of life remaining at a given age. It is denoted by ex, which means the average number of subsequent years of life for someone now aged x, according to a particular mortality experience...

 of females. Consequently, the sex ratio tends to reduce as age increases, and among the elderly there is usually an excess of females. For example, the male to female ratio falls from 1.05 for the group aged 15 to 65 to 0.70 for the group over 65 in Germany
Demographics of Germany
The Demographics of Germany were determined also by a series of full Census in Germany, with the most recent held in 1987. Since reunification, German authorities rely on a micro census....

, from 1.00 to 0.72 in the USA, from 1.06 to 0.91 in mainland China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

 and from 1.07 to 1.02 in India, which has a smaller proportion of very old people.

In the United States, the sex ratios at birth over the period 1970–2002 were 105 for the white non-Hispanic population, 104 for Mexican Americans, 103 for African Americans and Indians, and 107 for mothers of Chinese or Filipino ethnicity. Among Western European countries ca. 2001, the ratios ranged from 104 in Belgium to 107 in Switzerland, Italy, Ireland and Portugal. In the aggregated results of 56 Demographic and Health Surveys in African countries, the ratio is 103, though there is also considerable country-to-country variation.

Even in the absence of sex selection
Sex selection
Sex selection is the attempt to control the sex of the offspring to achieve a desired sex. It can be accomplished in several ways, both pre- and post-implantation of an embryo, as well as at birth...

 practices, a range of "normal" sex ratios at birth of between 103 to 108 boys per 100 girls has been observed in different economically developed countries, and among different ethnic and racial groups within a given country.

In an extensive study, carried out around 2005, of sex ratio at birth in the United States from 1940 over 62 years, statistical evidence suggested the following: For mothers having their first baby, the total sex ratio at birth was 1.06 overall, with some years at 1.07. For mothers having babies after the first, this ratio consistently decreased with each additional baby from 1.06 towards 1.03. The age of the mother affected the ratio: the overall ratio was 1.05 for mothers aged 25 to 35 at the time of birth; while mothers who were below the age of 15 or above 40 had babies with a sex ratio ranging between 0.94 to 1.11, and a total sex ratio of 1.04. This United States study also noted that American mothers of Hawaiian, Filipino, Chinese, Cuban and Japanese ethnicity had the highest sex ratio, with years as high as 1.14 and average sex ratio of 1.07 over the 62 year study period.

The sex ratio difference could be accounted for by the mass difference in sperm carrying Y chromosomes compared to those carrying X chromosomes. Sperm with Y (male) are 3% lighter (about 0.1 picograms out of the total 3.2 or 3.3pg mass of the entire 23 chromosomes). The 3-10% more males born could be a result of lighter sperm being more likely to reach the egg first (or at all) as they may achieve more velocity through the thick fluid.

Fisher's principle

Fisher's principle is an explanation of why the sex ratio of most species is approximately 1:1. Outlined by Ronald Fisher in his 1930 book, it is an argument in terms of parental expenditure. Essentially he argues that the 1:1 ratio is the evolutionarily stable strategy.

Natural factors

The natural factors that affect the human sex ratio are an active area of scientific research. Over 1000 articles have been published in various journals. Two of the often cited reviews of scientific studies on human sex ratio are by James., The scientific studies are based on extensive birth and death records in Europe, the Americas, Asia, Australia and Africa. A few of these studies extend to over 100 years of yearly human sex ratio data for some countries. These studies suggest that the human sex ratio, both at birth and as a population matures, can vary significantly according to a large number of factors, such as paternal age, maternal age, plural birth, birth order, gestation weeks, race, parent's health history, parent's psychological stress. Remarkably, the trends in human sex ratio are not consistent across countries at a given time, or over time for a given country. In economically developed countries, as well as developing countries, these scientific studies have found that the human sex ratio at birth has historically varied between 0.94 to 1.15 for natural reasons.

In a scientific paper published in 2008, James states that conventional assumptions have been:
  • there are equal numbers of X and Y chromosomes in mammalian sperms
  • X and Y stand equal chance of achieving conception
  • therefore equal number of male and female zygotes are formed, and that
  • therefore any variation of sex ratio at birth is due to sex selection between conception and birth.

James cautions that available scientific evidence stands against the above assumptions and conclusions. He reports that there is an excess of males at birth in almost all human populations, and the natural sex ratio at birth is usually between 1.02 to 1.08. However the ratio may deviate significantly from this range for natural reasons.

A 1999 scientific paper published by Jacobsen reported the sex ratio for 815,891 children born in Denmark between 1980–1993. They studied the birth records to identify the effects of multiple birth, birth order, age of parents and the sexes of preceding siblings on the proportion of males using contingency tables, tests and regression analysis. The secondary sex ratio decreased with increased number of children per plural birth and with paternal age, whereas no significant independent effect was observed for maternal age, birth order, or other natural factors.

A 2009 research paper published by Branum et al. reports the sex ratio derived from data in United States birth records over a 25 year period (1981–2006). This paper reports that the sex ratio at birth for the white ethnic group in the United States was 1.04 when the gestational age was 33–36 weeks, but 1.15 for gestational ages of less than 28 weeks, 28–32 weeks, and 37 or more weeks. This study also found that the sex ratios at birth in the United States, between 1981–2006, were lower in both black and hispanic ethnic groups when compared with white ethnic group.

The relationship between natural factors and human sex ratio at birth, and with aging, remains an active area of scientific research.

Environmental factors

Causes of stress during gestation, such as environmental temperature and maternal malnutrition generally appear to increase fetal deaths particularly among males, resulting in a lower boy to girl ratio at birth. Also, higher incidence of Hepatitis B virus in populations is believed to decrease the male to female sex ratio, while some unexplained environmental health hazards are thought to have the opposite effect. A 2007 survey by the Arctic Monitoring and Assessment Program noted abnormally low sex ratios in Russian Arctic villages and Inuit
The Inuit are a group of culturally similar indigenous peoples inhabiting the Arctic regions of Canada , Denmark , Russia and the United States . Inuit means “the people” in the Inuktitut language...

 villages in Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 and Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, and attributed this imbalance to high levels of endocrine disruptor
Endocrine disruptor
Endocrine disruptors are chemicals that interfere with endocrine in animals, including humans. These disruptions can cause cancerous tumors, birth defects, and other developmental disorders...

s in the blood of inhabitants, including PCBs
Polychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...

 and DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....

. These chemicals are believed to have accumulated in the tissues of fish and animals that make up the bulk of these populations' diets. However, as noted in the Social factors section below, it is important to exclude alternative explanations, including social ones, when examining large human populations whose composition by ethnicity and race may be changing.

A 2008 report demonstrates further evidence of effects of feminizing chemicals on male development in each class of vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

 species as a worldwide phenomenon, possibly leading to a decline in the sex ratio in humans and a possible decline in sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 counts. Out of over 100,000 recently introduced chemicals, 99% are poorly regulated.

Other factors that could possibly affect the sex ratio include:
  • Social status of the mother, known to be a factor in influencing the sex ratio of certain animals such as swine, but apparently not in humans
  • Whether the mother smokes
  • Whether the mother has a partner or other support network, although this correlation is widely considered to be the result of an unknown third factor
  • Latitude
    In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

    , with countries near the equator producing more females than near the poles.

Other scientific studies suggest that environmental effects on human sex ratio at birth are either limited or not properly understood. For example, a research paper published in 1999, by scientists from Finland’s National Public Health Institute, reports the effect of environmental chemicals and changes in sex ratio over 250 years in Finland. This scientific team evaluated whether Finnish long-term data are compatible with the hypothesis that the decrease in the ratio of male to female births in industrial countries is caused by environmental factors. They analyzed the sex ratio of births from the files of Statistics Finland and all live births in Finland from 1751 to 1997. They found an increase in the proportion of males from 1751 to 1920; this was followed by a decrease and interrupted by peaks in births of males during and after World War I and World War II. None of the natural factors such as paternal age, maternal age, age difference of parents, birth order could explain the time trends. The scientists found that the peak ratio of male proportion precedes the period of industrialization or the introduction of pesticides or hormonal drugs, rendering a causal association between environmental chemicals and human sex ratio at birth unlikely. Moreover, these scientists claim that the trends they found in Finland are similar to those observed in other countries with worse pollution and much greater pesticide use.

Social factors

Sex-selective abortion
Sex-selective abortion
Sex-selective abortion is the practice of terminating a pregnancy based upon the predicted sex of the baby. The selective abortion of female fetuses is most common in areas where cultural norms value male children over female children, especially in parts of People's Republic of China, India,...

 and infanticide
Infanticide or infant homicide is the killing of a human infant. Neonaticide, a killing within 24 hours of a baby's birth, is most commonly done by the mother.In many past societies, certain forms of infanticide were considered permissible...

 are thought to significantly skew the naturally occurring ratio in some populations, such as China, where the introduction of ultrasound scans in the late 1980s has led to a birth sex ratio (males to females) of 1.133 (2011 CIA estimate data). The 2011 India census reports India's sex ratio in 0-6 age bracket at 1.094. The 2011 birth sex ratios for China and India are significantly above the mean ratio recorded in the United States from 1940 through 2002 (1.051); however, their birth sex ratios are within the 0.98-1.14 range observed in the United States for significant ethnic groups over the same time period. Along with Asian countries, a number of European, Middle East and Latin American countries have recently reported high birth sex ratios in the 1.06 to 1.14 range. High birth sex ratios, some claim may be caused in part by social factors.

These practices are based on a cultural preference for one sex, typically males, over the other. A son is often preferred as an 'asset', since he can earn and support the family; a daughter is a 'liability' since she will be married off to another family, and so will not contribute financially to her parents. The patriarchal structure of a society is the single most important factor skewing the sex ratio in favor of males, accentuated in some cultures by the burden of raising a dowry
A dowry is the money, goods, or estate that a woman brings forth to the marriage. It contrasts with bride price, which is paid to the bride's parents, and dower, which is property settled on the bride herself by the groom at the time of marriage. The same culture may simultaneously practice both...

 for a daughter's marriage. Reported sex ratios at birth, outside the typical range of 103:100 to 107:100, thus call for an explanation of some kind.

In all such research, it is important to consider plausible alternative explanations. For example in some populations that have experienced declining sex ratios, researchers have suggested that ecological factors may be at work.

As an example of how the social composition of a human population may produce unusual changes in sex ratios, we can consider a study in several counties of California where declining sex ratios had been observed. Smith and Von Behren observe that: "In the raw data, the male birth proportion is indeed declining. However, during this period, there were also shifts in demographics that influence the sex ratio. Controlling for birth order, parents' age, and race/ethnicity, different trends emerged. White births (which account for over 80%) continued to show a statistically significant decline, while other racial groups showed non-statistically significant declines (Japanese, Native American, other), little or no change (black), or an increase (Chinese). Finally, when the white births were divided into Hispanic and non-Hispanic (possible since 1982), it was found that both white subgroups suggest an increase in male births." They concluded "that the decline in male births in California is largely attributable to changes in demographics."

Data sources and data quality issues

Reported sex ratios at birth for some human populations may be influenced not only by cultural preferences and social practices that favor the birth or survival of one sex over the other (more often favoring males than favoring females) but also by incomplete or inaccurate reporting or recording of the births or the survival of infants. Even what constitutes a live birth
Live birth
In human reproduction, a live birth occurs when a fetus, whatever its gestational age, exits the maternal body and subsequently shows any sign of life, such as voluntary movement, heartbeat, or pulsation of the umbilical cord, for however brief a time and regardless of whether the umbilical cord or...

 or infant death
Infant mortality
Infant mortality is defined as the number of infant deaths per 1000 live births. Traditionally, the most common cause worldwide was dehydration from diarrhea. However, the spreading information about Oral Re-hydration Solution to mothers around the world has decreased the rate of children dying...

 may vary from one population to another. For example, for most of the 20th century in Russia (and the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

), extremely premature newborns (less than 28 weeks gestational age, or less than 1000 grams in weight, or less than 35 centimeters in length) were not counted as a live birth until they had survived 7 days; and if that infant died in those first 168 hours it would not be counted as an infant death. This led to serious underreporting of the Infant mortality rate (by 22% to 25%) relative to standards recommended by the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...


When unusual sex ratios at birth (or any other age) are observed, it is important to consider misreporting, misrecording, or underregistration of births or deaths as possible reasons. Some researchers have in part attributed the high male to female sex ratios reported in mainland China
Mainland China
Mainland China, the Chinese mainland or simply the mainland, is a geopolitical term that refers to the area under the jurisdiction of the People's Republic of China . According to the Taipei-based Mainland Affairs Council, the term excludes the PRC Special Administrative Regions of Hong Kong and...

 in the last 25 years to the underreporting of the births of female children after the implementation of the one-child policy
One-child policy
The one-child policy refers to the one-child limitation applying to a minority of families in the population control policy of the People's Republic of China . The Chinese government refers to it under the official translation of family planning policy...

, though alternative explanations are now generally more widely accepted, including above all the use of ultrasound technology and sex-selective abortion
Sex-selective abortion
Sex-selective abortion is the practice of terminating a pregnancy based upon the predicted sex of the baby. The selective abortion of female fetuses is most common in areas where cultural norms value male children over female children, especially in parts of People's Republic of China, India,...

 of female fetuses and, probably to a more limited degree, neglect or in some cases infanticide
Infanticide or infant homicide is the killing of a human infant. Neonaticide, a killing within 24 hours of a baby's birth, is most commonly done by the mother.In many past societies, certain forms of infanticide were considered permissible...

 of females. In the case of China, because of deficiencies in the vital statistics
Vital statistics
Vital statistics are the information maintained by a government, recording the birth and death of individuals within that government's jurisdiction. These data are used by public health programs to evaluate how effective their programs are...

 registration system, studies of sex ratios at birth have relied either on special fertility surveys, whose accuracy depends on full reporting of births and survival of both male and female infants, or on the national population census from which both birth rates and death rates are calculated from the household's reporting of births and deaths in the 18 months preceding the census. To the extent that this underreporting of births or deaths is sex-selective, both fertility surveys and censuses may inaccurately reflect the actual sex ratios at birth.

Other gestational factors

A research group led by Ein-Mor reported that sex ratio does not seem to change significantly with either maternal or paternal age. Neither gravidity
In medicine, gravidity refers to the number of times a woman has been pregnant, regardless of whether the pregnancies were interrupted or resulted in a live birth....

 nor parity
Parity (medicine)
In biology, parity is a technical term that refers to the number of times a female has given birth to a fetus.It can lead to some ambiguity for events occurring between 20 and 24 weeks, and for multiple pregnancies.-Enumeration:...

 seem to affect the male-to-female ratio. However, there is a significant association of sex ratio with the length of gestation. These Ein-mor conclusions have been disputed. For example, James suggested that Ein-Mor results are based on some demographic variables and a small data set, a broader study of variables and larger population set suggests human sex ratio shows substantial variation for various reasons and different trend effects of length of gestation than those reported by Ein-Mor. In another study, James has offered the hypothesis that human sex ratios, and mammalian sex ratios in general, are causally related to the hormone levels of both parents at the time of conception. This hypothesis is yet to be tested and proven true or false over large population sets.

Gender imbalance

Gender imbalance is a disparity between male and females in a population. As stated above, males usually exceed females at birth but subsequently experience different mortality rates due to many possible causes such as differential natural death rates, war casualties, and deliberate gender control.

According to Nicholas Kristof and Sheryl WuDunn, two Pulitzer Prize-winning reporters for the New York Times, violence against women is causing gender imbalances in many developing countries. These authors report that more girls have been killed in the last 50 years, just because they were girls, than the number of males who were killed in all the wars of the 20th century. They detail rampant gendercide in the developing world, particularly in China, India and Pakistan.

As a contributing measure to gender imbalance in developing countries, Kristof and WuDunn's best estimate is that a girl in India, from 1 to 5 years of age, dies from discrimination every four minutes (132,000 deaths per year); that 39,000 girls in China die annually, within the first year of life, because parents didn’t give girls the same medical care and attention that boys received. The authors describe similar gender discrimination and gendercide in Congo, Kenya, Pakistan, Iraq, Bahrain, Thailand and many other developing countries.

Some of the factors suggested as causes of the gender imbalance are war
War is a state of organized, armed, and often prolonged conflict carried on between states, nations, or other parties typified by extreme aggression, social disruption, and usually high mortality. War should be understood as an actual, intentional and widespread armed conflict between political...

fare (excess of females, notably in the wake of WWI
World War I casualties
The total number of military and civilian casualties in World War I were over 35 million. There were over 15 million deaths and 20 million wounded ranking it among the deadliest conflicts in human history....

 in western Europe, and WWII
World War II casualties
World War II was the deadliest military conflict in history. Over 60 million people were killed, which was over 2.5% of the world population. The tables below give a detailed country-by-country count of human losses.-Total dead:...

, particularly in the Soviet Union
Demographics of the Soviet Union
According to data from the 1989 Soviet census, the population of the Soviet Union was 70% East Slavs, 12% Turkic peoples, and all other ethnic groups below 10%. Alongside the atheist majority of 60% there were sizable minorities of Russian Orthodox followers and Muslims According to data from the...

); sex-selective abortion and infanticide
Sex-selective abortion
Sex-selective abortion is the practice of terminating a pregnancy based upon the predicted sex of the baby. The selective abortion of female fetuses is most common in areas where cultural norms value male children over female children, especially in parts of People's Republic of China, India,...

 (excess of males, notably in People's Republic of China
Demographics of mainland China
The demographics of the People's Republic of China are identified by a large population with a relatively small youth division, which is partially a result of the People's Republic of China's one-child policy...

 as a result of the one-child policy
One-child policy
The one-child policy refers to the one-child limitation applying to a minority of families in the population control policy of the People's Republic of China . The Chinese government refers to it under the official translation of family planning policy...

, or in India
Demographics of India
The demographics of India are inclusive of the second most populous country in the world, with over 1.21 billion people , more than a sixth of the world's population. Already containing 17.5% of the world's population, India is projected to be the world's most populous country by 2025, surpassing...

); and large-scale migration, such as that by male labourers unable to bring their families with them (as in Qatar
Qatar , also known as the State of Qatar or locally Dawlat Qaṭar, is a sovereign Arab state, located in the Middle East, occupying the small Qatar Peninsula on the northeasterly coast of the much larger Arabian Peninsula. Its sole land border is with Saudi Arabia to the south, with the rest of its...

 and other Gulf countries). Gender imbalance may result in the threat of social unrest, especially in the case of an excess of low-status young males unable to find spouses, and being recruited into the service of militaristic political factions. Economic factors such as male-majority industries and activities like the petrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....

, agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...

, engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...

, military
A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...

, and technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...

 also have created a male gender imbalance in some areas dependent on one of these industries. Conversely, the entertainment
Entertainment consists of any activity which provides a diversion or permits people to amuse themselves in their leisure time. Entertainment is generally passive, such as watching opera or a movie. Active forms of amusement, such as sports, are more often considered to be recreation...

, banking, tourism
Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...

, fashion
Fashion, a general term for a currently popular style or practice, especially in clothing, foot wear, or accessories. Fashion references to anything that is the current trend in look and dress up of a person...

, and service
Customer service
Customer service is the provision of service to customers before, during and after a purchase.According to Turban et al. , “Customer service is a series of activities designed to enhance the level of customer satisfaction – that is, the feeling that a product or service has met the customer...

 industries may have resulted in a female-majority gender imbalance in some areas dependent on them.

One study found that the male-to-female sex ratio in the German state of Bavaria fell as low as 0.60 after the end of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 for the most severely affected age cohort (those between 21 and 23 years old in 1946). This same study found that out-of-wedlock births spiked from approximately 10–15% during the inter-war years up to 22% at the end of the war. This increase in out-of-wedlock births was attributed to a change in the marriage market caused by the decline in the sex ratio.

The Northern Mariana Islands
Northern Mariana Islands
The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands , is a commonwealth in political union with the United States, occupying a strategic region of the western Pacific Ocean. It consists of 15 islands about three-quarters of the way from Hawaii to the Philippines...

 have the highest female ratio with 0.77 males per female. Qatar
Qatar , also known as the State of Qatar or locally Dawlat Qaṭar, is a sovereign Arab state, located in the Middle East, occupying the small Qatar Peninsula on the northeasterly coast of the much larger Arabian Peninsula. Its sole land border is with Saudi Arabia to the south, with the rest of its...

 has the highest male ratio, with 2.87 males/female. For the group aged below 15, Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...

 has the highest female ratio with 0.96 males/female, and the Republic of Georgia
Georgia (country)
Georgia is a sovereign state in the Caucasus region of Eurasia. Located at the crossroads of Western Asia and Eastern Europe, it is bounded to the west by the Black Sea, to the north by Russia, to the southwest by Turkey, to the south by Armenia, and to the southeast by Azerbaijan. The capital of...

 and the People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

 are tied for the highest male ratio with 1.13 males/female (according to the 2006 CIA World Factbook).

The value for the entire world population
World population
The world population is the total number of living humans on the planet Earth. As of today, it is estimated to be  billion by the United States Census Bureau...

 is 1.01 males/female, with 1.07 at birth, 1.06 for those under 15, 1.02 for those between 15 and 64, and 0.78 for those over 65.

The "First World
First World
The concept of the First World first originated during the Cold War, where it was used to describe countries that were aligned with the United States. These countries were democratic and capitalistic. After the fall of the Soviet Union and the end of the Cold War, the term "First World" took on a...

" G7 members all have a gender ratio in the range of 0.95–0.98 for the total population, of 1.05–1.07 at birth, of 1.05–1.06 for the group below 15, of 1.00–1.04 for the group aged 15–64, and of 0.70–0.75 for those over 65.

Countries on the Arabian peninsula
Arabian Peninsula
The Arabian Peninsula is a land mass situated north-east of Africa. Also known as Arabia or the Arabian subcontinent, it is the world's largest peninsula and covers 3,237,500 km2...

 tend to have a 'natural' ratio of about 1.05 at birth but a very high ratio of males for those over 65 (Saudi Arabia 1.13, Arab Emirates 2.73, Qatar 2.84), indicating either an above-average mortality rate for females or a below-average mortality for males, or, more likely in this case, a large population of aging male guest workers. Conversely, countries of Eastern Europe
Eastern Europe
Eastern Europe is the eastern part of Europe. The term has widely disparate geopolitical, geographical, cultural and socioeconomic readings, which makes it highly context-dependent and even volatile, and there are "almost as many definitions of Eastern Europe as there are scholars of the region"...

 (the Baltic states
Baltic states
The term Baltic states refers to the Baltic territories which gained independence from the Russian Empire in the wake of World War I: primarily the contiguous trio of Estonia, Latvia, Lithuania ; Finland also fell within the scope of the term after initially gaining independence in the 1920s.The...

, Belarus
Belarus , officially the Republic of Belarus, is a landlocked country in Eastern Europe, bordered clockwise by Russia to the northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Its capital is Minsk; other major cities include Brest, Grodno , Gomel ,...

, Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...

, Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

) tend to have a 'normal' ratio at birth but a very low ratio of males among those over 65 (Russia 0.46, Latvia 0.48, Ukraine 0.52); similarly, Armenia
Armenia , officially the Republic of Armenia , is a landlocked mountainous country in the Caucasus region of Eurasia...

 has a far above average male ratio at birth (1.17), and a below-average male ratio above 65 (0.67). This effect may be caused by emigration
Human migration
Human migration is physical movement by humans from one area to another, sometimes over long distances or in large groups. Historically this movement was nomadic, often causing significant conflict with the indigenous population and their displacement or cultural assimilation. Only a few nomadic...

 and higher male mortality as result of higher Soviet era deaths; it may also be related to the enormous (by western standards) rate of alcoholism in the former Soviet states. Another possible contributory factor is an aging population, with a higher than normal proportion of relatively elderly people: we recall that due to higher differential mortality rates the ratio of males to females reduces for each year of age.

See also

  • List of countries by sex ratio
  • Lost boys (Mormon fundamentalism)
  • Missing women of Asia
    Missing women of Asia
    The phenomenon of the missing women of Asia is a shortfall in the number of women in Asia relative to the number that would be expected if there was no sex-selective abortion or female infanticide or if the newborn of both sexes received similar levels of health care and nutrition.The phenomenon...

  • Sex selection
    Sex selection
    Sex selection is the attempt to control the sex of the offspring to achieve a desired sex. It can be accomplished in several ways, both pre- and post-implantation of an embryo, as well as at birth...

  • Sex-selective abortion and infanticide
  • XY sex-determination system
    XY sex-determination system
    The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex. Males have two distinct sex chromosomes , and are called...