In anthropology and demographythe human sex ratio is the ratio of males to females in a population.
More data is 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 Men above women difficult. Like most sexual species, the sex ratio in humans is approximately 1: Due to higher female fetal mortality,  the sex ratio at birth worldwide is commonly thought to be boys to girls although this value is subject to debate in the scientific community.
The sex ratio for the entire world population is males to females est. Gender imbalance may arise as a consequence of various factors including natural factors, exposure to pesticides and environmental contaminants,   war casualties, sex-selective Men above womeninfanticides, aging, and deliberate gendercide.
Human sex ratios, either at birth or in the population as a whole, are reported in any of four ways: If there aremales andfemales the ratio of males to females is 1. Scientific literature often uses the proportion of males. This article uses the ratio of males to females, unless specified otherwise.
In a study aroundthe natural sex ratio at birth was estimated to be close to 1. This assumption has been questioned by some scholars. Infant mortality Men above women higher in boys than girls in most parts of the world.
This has been explained by sex differences in genetic and biological makeup, with boys being biologically weaker and Men above women susceptible to diseases and premature death. It has been proposed that these environmental factors also explain sex differences in mortality.
For example, in the United States, as ofan adult non-elderly male is 3 to 6 times more likely Men above women become a victim of a homicide and 2.
For example, the male to female ratio falls from 1. In the United States, the sex ratios at birth over the period — were 1. In the aggregated results of 56 Demographic and Health Surveys  in African countries, the ratio is 1. There is controversy whether sex ratios outside the range are due to sex-selection, as suggested by some scholars, or due to natural causes.
Some scholars argue that strong socioeconomic factors such as the dowry system in India and the one child policy of China are responsible for prenatal sex-selection. In a widely cited article,  Men above women Sen supported such views.
Other researchers argue that an unbalanced sex ratio should not be automatically held as evidence of prenatal sex-selection; Michel Garenne reports that many African nations have, over decades, witnessed birth sex ratios belowthat is more girls are born than boys. In an extensive study, carried out aroundof sex ratio Men above women birth in the United States from over 62 years, statistical evidence suggested the following: Fisher's principle is an explanation of why the sex ratio of most species is approximately 1: Outlined by Ronald Fisher in his book, it is an argument in terms of parental expenditure.
Essentially he argues that the 1: The natural factors that affect the human sex ratio are an active area of scientific research. Over articles have been published in various journals. Two of the often cited reviews of scientific studies on human sex ratio are by W.
A few of these studies extend to over 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, Men above women as paternal age, maternal age, plural birth, birth order, gestation weeks, race, parent's health history, and 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. In a scientific paper published in James states that conventional assumptions have been:.
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, Men above women the natural sex ratio at birth is usually between 1.
However the ratio may deviate significantly from this range for natural reasons. A scientific paper published by Jacobsen reported the sex ratio forchildren born in Denmark between — 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 research paper published by Branum et al. This study also found that the sex ratios at birth in the United States, between —, 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 Men above women scientific research.
Various scientists have examined the question whether human birth sex ratios have historically been affected by environmental stressors such as climate change and global warming. Cold weather stressors simultaneously extend male longevity thereby raise human sex ratio in its older age bracket.
They find an increased excess of male births during periods of the exogenous stress World War II and during warm years. In the warmest period over the years, Men above women birth sex ratio peaked at about 1.
Causes of stress during gestation, such as 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 Men above women virus in populations is believed to increase the male to female sex ratio, while some unexplained environmental health hazards are thought to have the opposite effect.
The effects of gestational environment on human sex ratio are complicated and unclear, with numerous conflicting reports.
For example, Oster et al. They found no effect on birth sex ratio from Hepatitis B Men above women in either the mothers or fathers. A survey by the Arctic Monitoring and Assessment Program noted abnormally low sex ratios in Russian Arctic villages and Inuit villages in Greenland and Canadaand attributed this imbalance to high levels of endocrine disruptors in the blood of inhabitants, including PCBs and DDT.