Former Irish President Mary Robinson was just making polite conversation when she asked an Ethiopian teenager about her wedding day.
The 16-year-old had already been married a year.
"She looked at me with the saddest eyes and said, 'I had to drop out of school,'" Robinson said in a telephone interview.
"That conveyed to me the reality," said Robinson, the first woman to serve as Ireland's president and former U.N. high commissioner for human rights. "Her life, as far as she is concerned, had more or less ended."
Robinson said keeping girls in school was one of the most important things policymakers could do to address the coming challenges of an ever-increasing population, predicted by the United Nations to reach 7 billion at the end of the month.
"European countries are concerned about aging populations as is Japan, but this is much less of an issue than the huge bulge of people which we are going to see over the next 40 years when the population goes from 7 billion to 9 billion people," she said.
"Almost all of that increase will be in poor developing countries, so that we have a very big demographic challenge."
Family planning experts worry in particular about the looming population boom in sub-Saharan Africa.
In May, the United Nations projected the world population would reach 9.3 billion in 2050 and 10.1 billion by 2100. Much of that growth will come from Africa, where the population is growing at 2.3 percent a year -- more than double Asia's 1 percent growth rate. If that rate stays consistent, which is not certain, Africa's population will more than triple to 3.6 billion by 2100 from the current 1 billion.
Joel Cohen, a professor of population studies at Rockefeller University and Columbia University in New York, said universal secondary education offered a way to reduce population in high-fertility regions.
In addition to providing information about contraception, a secondary education motivates women to reduce their own fertility, improve the health of their children and allows them to move from a mind-set of having many children in the hopes that some will survive to improving the quality of each child's life, Cohen wrote in the journal Nature.
"Although there are other factors at work, in many developing countries, women who complete secondary school average at least one child fewer per lifetime than women who complete primary school only," he added.
Most family planning experts warn against extreme coercive population control measures, such as China's "One Child" policy, which since 1980 has limited parents to only one child. The uniquely draconian policy succeeded in limiting the growth of the world's largest population but led to other problems such as skewing the demographic toward males and creating a disproportionate aging population.
Dr. Babatunde Osotimehin, former Nigerian health minister and executive director of the United Nations Population Fund or UNFPA, told Reuters his focus is very much on empowering women in such a way as to change the cultural norms.
"When a young woman goes through at least secondary education, her children survive better, physically they mature, emotionally they mature, and because they have education, they are able to make choices," Osotimehin said.
"It is not just their ability to make the choice about family planning. It's also that they have power of their own, which enables them to live a life of dignity and respect."
Lack of access
Africa is full of examples of countries struggling with efforts to attain full educational enrollment in the face of high fertility, said Dr. Fred Sai, Ghanaian physician and former director general of the International Planned Parenthood Federation.
"Family planning can help to slow down population growth in those regions and countries where the fertility rates are over two (children) per woman and especially where women want and need family planning and have no access."
According to UNFPA, more than 215 million women want to delay or prevent pregnancies but lack modern contraception.
Family planning experts are frustrated by lack of progress on commitments made to improve women's sexual and reproductive health at the 1994 International Conference on Population and Development in Cairo.
Progress has been stalled in part, they say, by increasing pressure from social conservatives, especially in the United States, who equate family planning with abortion.
"Family planning is so much more than just access to abortion," said Lyndon Haviland, a senior health fellow at the Aspen Institute, a nonpartisan think tank in Washington.
"It's about healthy pregnancies. It's about building the future for young girls," Haviland said.
"It's kind of ironic to me ... The easiest way to prevent abortion is to fully fund family planning because abortion means a woman didn't have access to family planning, she wasn't able to control what was happening with her body."
Haviland and others argue that family planning is a development issue and the lack of it can increase political tensions.
In Yemen, which has the highest rate of unmet need for family planning, the population has doubled in less than 20 years and its high fertility rate of some six children per woman is pressuring that nation's fragile economy, Isobel Coleman of the U.S. Council on Foreign Relations said in a recent policy report.
"Increasing access to family planning would help improve Yemen's long-term prospects for achieving per capita growth and stability," Coleman said.
According to Coleman, 80 percent of all outbreaks of civil conflict between 1970 and 2007 occurred in countries with very young populations and that threat dissipates as birth rates decline.
In Somalia, 70 percent of the population is under age 30, yet only 1 percent of married women in Somalia have access to modern contraception, and the country has one of the highest rates of population growth in the world.
That is something Robinson observed while visiting Somalia in July to draw attention to the famine, which has killed nearly 30,000 children.
Hope children survive
"One of the ways you open up a conversation is to ask how many children do you have. Not a single woman said less than six children," Robinson said.
"They were having seven, eight, nine children because they hoped maybe one or two might survive -- an appalling situation for any mother to be in."
Robinson recalls her own struggle growing up in the west of Ireland in the 1950s.
"It was very much a Catholic-dominated environment," she said. "I became increasingly aware of the many ways in which women were made to feel that their role was to marry and become mothers. It was even in the constitution that the place of the woman was in the home."
There was also no access to modern contraception, something Robinson set out to change. She was elected to Ireland's Senate in 1969, and introduced a bill in late 1970 to change the law making it a crime to buy or sell a condom.
Robinson was denounced from church pulpits but held firm.
"It brought home to me that it's not just a matter of changing legislation. It's a deeply cultural behavioral issue," she said.
"There has to be very wide discussion and the real change has to come through education and through a bottom-up approach in communities."
Robinson urged governments not to turn to coercive population control strategies.
"We know what works. What works is education of girls and women and access to healthcare, so that mothers will know their children will survive," she said.