Animal Kings: Ants, like these workers carrying eggs to a plant's leaf after rain flooded their nest, have a combined biomass estimated in the billions of tons. Gurinder Osan/AP hide caption

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The population of Karachi, Pakistan, has been boosted by a new influx of young people. And now the city, seen here during a political rally in January, is making a bid to attract global elites.

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A South Korean man takes a photo of his baby during a picnic in Seoul, in 2009. After years of promoting family planning, South Korea is seeing unprecedented numbers of women staying single into their 30s — up from a handful a generation ago to 40 percent. Jung Yeon-Je/AFP/Getty Images hide caption

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The world's population has just hit 7 billion people and continues to grow. Population experts are concerned about the rise in consumption that will accompany the increase in people. One California home builder, ZETA Communities, designs and builds small, highly energy-efficient homes.

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itoggle caption Zeta Communities

Lujiazui, Shanghai's financial district, includes the world's third- and sixth-tallest buildings. The city's population is 23 million.

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Several babies born today have been deemed the symbolic 7 billionth person — including a little girl named Nargis in Lucknow, India. Here she is with her mother, Vinita.

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Newborns lie together at a district women's hospital in Allahabad, in India's most populous state of Uttar Pradesh. Fifty-one babies are born in India every minute.

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Indian schoolchildren write English alphabets on slates at a primary school outside Hyderabad in June. India is on track to overtake China as the most populous nation in just 16 years. Noah Seelam/AFP/Getty Images hide caption

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Immigrants like these Indians at a Sikh festival in Barcelona are bolstering Europe's stagnant population growth rate. Randy Olson/National Geographic hide caption

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Sharing a hillside with high-rise apartment dwellers, children dance at a shop in one of the squatter communities that ring Caracas, a city of 3 million. Today, one in seven people live in slums. Providing them with better housing and education will be one of the great challenges facing a world of 7 billion people and counting. Jonas Bendiksen/Magnum Photos hide caption

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