Which wildlife conservation marketing innovation first introduced the concept of 'adopting' an endangered animal as a donation strategy?

Conservation organizations often use innovative marketing strategies to raise awareness and funds for endangered species. Some campaigns have become iconic in the wildlife protection space, dramatically changing public perception and engagement. This trivia question focuses on one particularly successful marketing innovation that revolutionized how conservation organizations connect their causes with supporters worldwide.

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World Wildlife Fund's symbolic animal adoption program (1973)
National Geographic's 'Photo Ark' campaign (2006)
The Nature Conservancy's 'Adopt an Acre' program (1991)
Jane Goodall Institute's 'ChimpanZoo' sponsorship (1984)