Many museums and zoos run largely from gifts and donations. This wall has plaques that contributors pay as a way to thank or remember someone that had contributed to the zoo. The larger the plaque, the higher the contribution.
Some places now sell bricks for a fee. A well known internet podcaster recently helped build a broadcast studio with funding from bricks he sold. The contributors could also have text or their company logo laser engraved onto the face of the brick. With my luck, if I had bought one it would have been installed behind the toilet.