Frans de Waal Frans de Waal

Two white-headed capuchin monkeys (also known as the white-faced capuchin or white-throated capuchin) on Gorgona island, off Colombia's Pacific coast. AFP/Getty Images hide caption

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AFP/Getty Images

Bonobos at the Lola ya Bonobo sanctuary near Kinshasa in the Democratic Republic of Congo in 2006. Issouf Sanogo/AFP/Getty Images hide caption

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Issouf Sanogo/AFP/Getty Images