In the modern society, zoos are almost indispensable places in large cities for people to visit. In some large zoos, there are various animals from space to sea, and from primitive invertebrates to advanced and intelligent mammals. In the zoos, all animals, including those rare animals, such as panda, Africa elephant, and North-East tiger, could enjoy good care and protection away from any hurt. However, along with the stronger natural environmental protection consciousness, many people think that to put animalssintossmall cages will change their living instincts, and therefore break the ecological balance.
　　Viewed from the basic relations between animals and human beings, animals should have the equal freedom with human beings. They are all forms of life. Animals have their own living instinct, and it is this instinct that forms the biological chain of the Earth. This relation is called "Ecological Balance" academically. For example, insect-bird-snake. If most birds in a region are killed and lockedsintoscages by human beings, the pests will eat out all crops, and snakes will lose a large part of food (bird)-resources, therefore leading to starvation and death.
　　This opinion sounds ideal theoretically. However in reality, human beings and other animals cannot stay together peacefully on the Earth. Because of human beings' lust for fortune, many valuable animals are killed or sold, especially those endangered species. Therefore, zoos appear as an active way for people to protect those poor animals. First, this is an action not only for animals but also for human being itself. Once the biological chain is broken, human beings will be punished inevitably. Next, zoos can serve a purpose of educating and entertaining people, narrowing the distance between human beings and animals. Last, zoos can be a scientific study center to rescue more endangered spices and make animals better serve people's need.
　　The key point of this topic is freedom or protection. In my opinion, those two aspects can be unified. It is necessary to keep animals in zoos for the purpose of protection, teaching and study. Let's think it further, the purpose of all these actions is to make animals live happier, therefore, maintain the ecological balance, hence protect our own living environment.