There is an unsettling statistic that bodes ill for Asia: The region has roughly 100 million more men than women, with the biggest gulfs seen in China and India. In some places, however, the imbalance skews the other way. In either case, the gender gap is causing problems, ranging from economic inefficiency to fewer marriages to more violent crime -- all of which makes it harder for Asia to keep its impressive growth on an even keel.

Jhajjar looks much like any other rural area in India -- groups of people sitting together on dusty roadsides as cars and motorcycles pass by, rows of small shops and street stalls lining the central area. But this district, located 50km west of New Delhi in Haryana State, has long been infamous for one thing: Its unnaturally high ratio of male births.

The natural sex ratio at birth is around 105 boys per 100 girls. In the 2011 census, however, Jhajjar had 67,380 boys and 52,671 girls ages zero to six, or 128 boys per 100 girls, making it one of India's most-skewed districts in terms of child sex ratio. The nationwide ratio was 108 boys per 100 girls.

On a recent afternoon in March, the majority of people in the central part of the district were male. All of the 10 or so men in their 30s to 60s who talked to the Nikkei Asian Review said they have one or more sons. "Everyone wants a boy," said one, a 43-year-old self-employed man with two teenage sons. "Girls go to another family after their marriage, so they will not take care of us in the future." He said he knows someone who terminated a pregnancy after finding out the unborn child was female.

For reasons ranging from deep-rooted historical and cultural factors to recent decisions by policymakers, sex-selective abortions are still all too common in Asia. Carried out millions of times across the region, they are creating population trends with far-reaching social and economic consequences.

Like Jhajjar, many places in India have skewed gender ratios because girls were either aborted before birth or killed through neglect as children. A major reason for this is financial. In addition to India's patrilocal culture, in which the bride goes to live with her husband's family after marriage, dowries are a heavy burden, sometimes costing more than a family earns in a year -- many parents start to save up for them as soon as a daughter is born. "Daughters cost a lot, and their contribution to the family is not big. That's one of the reasons for the preference for sons," according to Yuiko Nishikawa, a professor of Indian demography at Japan's Josai University.

In the past, couples often had children until the first son was born, which also distorted the gender balance in the total population. But with educational costs rising, people are having fewer children. This, combined with the development of technology for identifying the sex of unborn babies, means the prevalence of male births has become more pronounced, Nishikawa said. As a result, India now has millions more men than women. According to data from the United Nations' World Population Prospects (The 2015 Revision), India's sex ratio for the total population stood at 107.6 men per 100 women in 2015.

This "male surplus" is not limited to India. The trend spreads across Asia, particularly in China and Vietnam. According to the UN estimate, there were 2.24 billion men in Asia and the Middle East in 2015, compared with a female population of 2.14 billion. The population gap -- a staggering 100 million -- has widened 70% since 1985.

The picture across much of Asia, particularly in areas with a combination of a patriarchal society and weak social safety net, stands in marked contrast with that of the West. Europe and North America registered a female surplus of 26 million and 3 million, respectively, in 2015. In countries with widely available health care and longer life expectancies for women, there is normally a female surplus.

MISSING OUT In India, the workforce -- like the population and the culture -- is dominated by men. According to estimates by the International Labor Organization, the workforce participation rate for women was 27% in 2014, far below the global average of 50%.

The Indian economy is growing rapidly, at some 7% annually. But the imbalance in its workforce means the country is missing out on a sizable chunk of potential growth. According to a 2015 report by McKinsey Global Institute, a research arm of McKinsey & Co., India's gross domestic product could be 60% higher in 2025 compared with a business-as-usual scenario if women played the same role in the workforce as men.

"Women are productive, but their productivity does not get commercialized," said Mriganka Dadwal, founder of a Delhi-based nonprofit organization dedicated to empowering women.

Some companies have recognized this missed potential and have started addressing the problem. Motherson Sumi Systems' wiring harness plant in Noida, Uttar Pradesh, employs some 2,900 workers, of which 58% are female. The company said the number of female workers is increasing every year.

Women take part in a training program for making wiring harnesses more efficiently at Motherson Sumi Systems' Noida plant in northern India. (Photo by Ken Kobayashi)

"Female workers are far more efficient than their male counterparts, because the nature of the job here requires a very high level of concentration and consistency, which you find more in females as compared to males," said a factory official who asked not to be named. The company offers creches for workers' children, as well as transportation covering at least part of their commutes.

New businesses aimed specifically at helping women join the workforce are also on the rise.

In front of a Delhi Metro station on the outskirts of the capital, three pink bike taxis and their female drivers, wearing colorful scarves and helmets, stood next to traditional three-wheeler taxis on one recent afternoon. They belong to Bikxie Pink, a women-only bike taxi service its founders say is the first of its kind in India. Launched in January 2016, Bikxie operates like many ride-hailing services: A customer books a ride using a mobile app, a female driver arrives and puts her on the back seat, and the two set off.

Drivers working for Bikxie Pink, a bike taxi service by and for women, wait for customers around a metro station in Gurgaon, near New Delhi. (Photo by Ken Kobayashi)

In a country that has seen a number of violent sexual crimes in public transportation, making sure working women can commute safely is crucial. Bikxie COO Divya Kalia said most conventional transportation options from station to office are unregulated and unsafe. "Nobody is looking into what routes they are taking and who they are taking. A male driver can verbally or [otherwise] abuse a female passenger. There is nothing she can do about that," she said.

Now in its second year, Bikxie operates nearly 20 women-only bikes in three cities. About 90% of its passengers are commuters traveling between the office and the nearest metro station. Bikxie charges 20 rupees ($0.31) for the first 2km, and each bike carries 20 to 25 passengers a day. Kalia said the company aims to add five more cities by the end of this year as it anticipates further demand for its services.

Sairee Chahal is CEO of Sheroes, an online job-matching portal for women. "Companies need women's potential," Chahal said. Launched in 2014, Sheroes already has around 1 million member profiles, and 16,000 companies are offering jobs through the site, including executive positions. The platform also offers its members training in areas such as programming.

"Indian women are seen as a liability [for their families]," Chahal said, noting that most women don't have access to or control over the family's financial resources. She believes the gender imbalance in the population will improve if women can earn money and become more independent. Then, she said, they will be seen as "good financial assets."

Businesses like Sheroes show there is money to be made in closing the gender gap.

The government, too, is starting to take action. Its five-year plan through 2017 targets improving the child sex ratio (covering ages zero to six) from the 2011 census figure -- 919 girls to 1,000 boys -- to 950 girls per 1,000 boys. To achieve this, the government in 2015 launched the "Beti Bachao, Beti Padhao (Save daughter, educate daughter)" campaign, which had spread from an initial 100 districts to 161 by March this year.

As for workforce participation, the parliament in March passed a bill to increase maternity leave from 12 weeks to 26 weeks for a woman's first two children, with maternity leave for subsequent children to remain at 12 weeks. Prime Minister Nerendra Modi tweeted that the passage of the bill is "a landmark moment in our efforts towards women-led development."

MORE THAN MONEY The potential costs of a male surplus go well beyond business. Studies indicate a slight correlation between sex ratios among young adults and violent crime and theft.

China is another country with a major gender imbalance -- 106.2 men per 100 women in 2015, according to the U.N. estimate. The country's violent crime rate rose in tandem with the male-to-female sex ratio of 16- to 25-year-olds, according to a 2013 study by Lena Edlund at Columbia University and others. Gender imbalance will "produce men who cannot marry, which could result in an increase of complaints, sexual crimes and girls being kidnapped, as well as human trafficking," said Toru Suzuki, director of the Department of Population Structure Research at the National Institute of Population and Social Security Research in Tokyo.

The impact of China's gender imbalance is already spreading beyond the country's borders.

The Cambodian Human Rights and Development Association said it received 15 complaints last year about Cambodian women being trafficked to China for marriage purposes. The organization sees these reported cases as just the tip of the iceberg.

"Human trafficking, including to China for the purpose of marriage, reduces human resources in Cambodia and inhibits people's ability to positively contribute towards the development of the country," said Chhan Sokunthea, head of the organization's section for women's and children's rights. "In addition, unlike migration, human trafficking does not have positive benefits on the home community in the form of remittances."

"[Trafficked] women and girls are often subject to severe human rights violations, including being detained, beaten, raped, subjected to forced labor or forced pregnancies, and cut off from their families," she added. "In addition, many repatriated survivors face increased discrimination in their home communities in comparison to other kinds of trafficking, such as labor abuse."

China, influenced by Confucianism, has a traditional preference for sons. The government's one-child policy, which lasted from 1979 to 2015, led even more people to choose baby boys over girls, either through abortion or infanticide. The result decades later has been a severe shortage of brides.

Some areas in China practice a kind of reverse dowry, in which the man is required to provide a sum of money to his betrothed, often several times his annual salary. As a result, some men turn to human traffickers to find a non-Chinese bride for less money. Many of these women are from neighboring countries, including Vietnam and Cambodia.

Recent data suggests the male surplus is smaller than has long been thought because, researchers argue, many parents did not register the birth of daughters. But trafficking cases suggest that Chinese men face a real difficulty in getting married. The number of births in China increased by 1.31 million, or 7.9%, in 2016 from the previous year, but the imbalance in the marrying age will continue for many years.

Vietnam seems to be following a similar path. The country has male-oriented kinship systems, more deeply rooted in the northern parts of the country closest to China, which is more traditional. Sons are expected to live with their parents and care for them in their old age. Sons are also supposed to carry out religious rites for their parents after they die and carry on the practice of ancestor worship. In return for these heavy responsibilities, sons usually inherit the main part of the family property. Though it is illegal, many couples still abort female fetuses to ensure that their first child is boy.

The sex imbalance at birth in Vietnam increased from 106.2 boys per 100 girls in 2000 to 112.8 boys per 100 girls in 2015, and it is expected to reach 125 boys per 100 girls by 2020, according to the General Office of Population and Family Planning, part of the Ministry of Health. The ministry has proposed giving money to parents who have a daughter, but nothing has been approved so far.

As the "surplus generation" reaches marrying age, less traditional methods of finding mates may grow more prevalent. According to a local media report, a Vietnamese government official warned that the surplus of men could to lead to a surge in "imported brides" as unmarried local men pay marriage brokers to find them wives, mostly from neighboring countries.

This male-heavy gender imbalance is not seen in some emerging nations, such as Thailand, Indonesia and the Philippines, partly because these countries have matriarchal cultures. However, the demographic changes in India, China and Vietnam, which account for about 60% of Asia's population, have a big impact on the rest of the region.

These three countries are also in the midst of rapid economic growth. If their gender imbalances fetter their own growth, it could easily end up affecting neighboring nations.

It is difficult to change the deeply ingrained cultural preference for sons. But as India's Motherson Sumi, Bikxie and Sheroes show, there are steps private sector can take to address the imbalance and help women achieve higher earning power.

The public sector should continue its efforts to crack down on prenatal sex-selections, according to Suzuki of the National Institute of Population and Social Security Research. He also points to the need for better social safety nets, as many parents currently have sons as a form of "social security" for the future. "If parents could live on a public pension, they wouldn't conduct sex-selective abortions, so we can say imbalances would naturally disappear by introducing enough social security protection," he said.

Primary reporting from New Delhi, with contributions from Nikkei staff writer Kiran Sharma