The constant breeding of animals in zoos leads to "surplus" animals, or those who are too closely related to other animals in breeding programs. The killing and public dissection of Marius the giraffe in 2014 showed the world how callously zoos treat animals that are surplus to their breeding or space requirements.

How does captivity affect animals?

Previous studies have indicated that animals kept in captivity over many generations have smaller brains – and therefore less brain function – than their wild counterparts. It's thought that they become adapted to a less-stimulating environment, leading to an irreversible decrease in brain size.

What are the negative effects of animals in captivity?

Animals in zoos do not have any control over their lives, leading them to become depressed and frustrated. This inherent stress, called zoochosis, forces them to exhibit self-destructive, repetitive behavior.