LAGOS, Nigeria — One South African mother, just 19, named her newborn “Enough” and shrugged off a nurse who questioned whether she was old enough to know how many children she wanted.
In Nigeria, newborn twins have to share a bassinet in a crowded public hospital that doesn’t have enough electricity.

“Where there is life, there is hope,” their mother said. But as the global population tops 7 billion, fears were stirred anew on how the planet will cope with the needs of so many humans.

STRAINS OF POPULATION GROWTH

The United Nations marked the milestone Monday, but it is impossible to pinpoint the arrival of the globe’s 7 billionth occupant because millions of people are born and die each day.

At Lagos Island Maternity Hospital, the strain of caring for a burgeoning population was evident as ceiling fans struggled to cool a hot ward filled with incubators. While Nigeria is oil-rich, it does not produce nearly enough power for its more than 160 million people.

Seun Dupe, 32, a hairdresser who gave birth to twins Oct. 23, remained an optimist despite the staggering burden facing Africa’s most populous nation and other developing countries. Her babies spent Monday squirming beneath a mosquito net.

Dupe was confident that new lives will ensure Nigeria’s future as “a great nation.”

‘SEVEN BILLION … IS A CHALLENGE’

U.N. Secretary-General Ban Ki-moon said the day was “not about one newborn or even one generation” but “about our entire human family.”

At a news conference in New York, he noted “a world of contradictions” – famine in the Horn of Africa, fighting in Syria and elsewhere and widespread protests against economic inequality.

“Seven billion population is a challenge,” he said, and “at the same time, an opportunity, depending upon how the international community prepares for that challenge.”

In South Africa, Nozipho Goqo, an unemployed 19-year-old from Johannesburg, gave birth Monday to a boy, her first child. She gave him a Zulu name – Gwakwanele – that means “enough.”

A nurse teased Goqo that she was too young to know whether this would be her last baby. Goqo smiled and said she was sure.

SHORT ROAD TO 8 BILLION

Demographers say it took until 1804 for the world to reach 1 billion people, and a century more until it hit 2 billion in 1927. Soon the numbers began to cascade: 3 billion in 1959, 4 billion in 1974, 5 billion in 1987, 6 billion in 1998.

The U.N. estimates the world population will reach 8 billion by 2025 and 10 billion by 2083. But the numbers could vary widely, depending on life expectancy, access to birth control, infant mortality rates and other factors.

In Uttar Pradesh, India – the most populous state in the world’s second-most populous country – officials said they’d appoint seven girls born Monday to symbolize the 7 billion.

India, which struggles with a deeply held preference for sons and a skewed sex ratio because of millions of aborted female fetuses, is using the day to highlight that issue.

“It would be a fitting moment if the 7 billionth baby is a girl born in rural India,” said Dr. Madhu Gupta, a gynecologist. “It would help in bringing the global focus back on girls, who are subject to inequality and bias.”

Meanwhile, China, which at 1.34 billion people is the world’s most populous nation, said it would stand by its one-child policy, a set of restrictions launched three decades ago that limit most urban families to one child and most rural families to two.

“Overpopulation remains one of the major challenges to social and economic development,” said Li Bin, a population planning official. He said the population of China would hit 1.45 billion in 2020.