National Geographic Ultimate Explorer host Lisa Ling examines the consequences of China's two-decades-old "one-child policy," designed to curb the country's exploding population. Due to cultural, social, and economic factors, traditional preference leans toward boys, so girls are often hidden, aborted, or abandoned. As a result, tens of thousands of girls end up in orphanages across China. Today, more than one quarter of all babies adopted from abroad by American families come from China—and nearly all are girls. Ling joins some of these families as they travel to China to meet their new daughters for the first time. Along this emotional journey, she shares in the joy of these growing families and also witnesses firsthand China's gender gap, its roots, and its possible repercussions. Join Ling as she explores the many complex issues surrounding China's attempt to slow its swelling tide of humanity.