Already within the Middle Ages, kings across Europe maintained a zoo at their royal courts. It was a common way to demonstrate power and wealth.

Despite humans' professed concern for animals, the zoo purpose was never changed. Zoos are still "collections" of interesting "items”, demonstrating human’s power and domination. Animals in zoos are treated like a stamp collection. The more species, the better, especially if they are large animals from foreign places that the public would be willing to pay money to watch. It doesn’t matter if the zoo has only one animal of each species, or if the space is much too small for the animal. The "specimens" are arranged in cages to make it easy to observe them at close range, at all times.

Zoos talk a lot about their serious scientific research, their total commitment to conservation, and their vital role as educators. Meanwhile, people do what they have always done. They go to the zoo to be entertained.
The expectation of the visitors is that the animal would please them. Humans demand to be taken notice of and they are insulted to find that usually the animals ignore them. They expect the animals to entertain each and every one of them as “come here and say hello! Do something cute”. The ugliest examples of humans demand for attention includes teasing, banging on cages and throwing things at them.
Zoo fosters the assumption that humans are the center of the universe.

Let's examine what effect zoos have on humans and on non-human animals:

Caged animals are deprived of their normal society, their families and mates.
Tigers can’t run, birds can’t soar the sky, monkeys can’t swing through the trees, and elephants can’t roam over large distances.
Animals which would naturally roam for tens of miles a day, tread the same few paces. Some of the fastest animals on earth live in pens so small that they could not gather pace to a trot, let alone full speed.
Some zoo enclosures deprive the prisoners’ most basic behaviors including exercise, social interaction and bathing.

Animals that naturally live in large herds or family groups are often kept alone, or at most, in pairs. Foraging and mating behaviors are virtually eliminated by regulated feeding and breeding regimens. The animals are closely confined so they lack privacy. Solitary and shy animals are often imprisoned in cages with viewing from all sides.
Having no mental stimulation or physical exercise, results in abnormal and self-destructive behavior called Zoochosis.

Deep instincts that have evolved over thousands of years can't find any outlet. The result is boredom and stress. The animals show signs of mental disturbance through abnormal behaviors. The most common one is a repeated movement: rocking from side to side, pacing up and down or round and round, waving or circling the head, over and over again.
Sometimes they become apathetic and just sit in one place. Such obsessive and repetitive behaviors, known as stereotypic behavior, including self-mutilation, are common amongst zoo animals as a result of frustration and boredom.

With nothing to do, these animals go out of their minds

The physical, mental, and social aspects of the life of elephants are very complex. Wild elephants frequently bathe in mud and water. It maintains their skin and it is also a social phenomenon. Elephants also dust themselves with dry earth to protect themselves from the sun and insect bites.
For elephants in captivity, these behaviors are not possible.
An elephant to whom herd and social structure are so important, is imprisoned alone. As a result elephants spend most of their time engaging in abnormal behaviors, such as repeated head bobbing or biting cage bars.

Polar bears suffer severe mental disturbance in zoos. They spend about third of their time pacing. Another severe sign of distress is bears pulling out their own fur to the point that the belly and hind legs are bald. The death rate of cubs in captivity is twice as high as in the wild.

This is what boredom, frustration, habitat deprivation, stress and loneliness cause:

Great apes and elephants rock, sway or shift repeatedly from side to side.
Giraffes are licking the walls and chewing the bars of their pens.
Jaguars chew the end of their tail, which has become completely bald.
Giraffes, llamas and some monkey species, are twisting and rolling their neck unnaturally, often flicking the head around or bending the neck back. It can be combined with a pacing behavior.
Caged big cats pace the same path again and again.
Primates may over groom themselves or each other and this can lead to self-mutilation.
Disturbed maternal behavior may also involve over grooming but also the rejection or killing of young.
Abnormal behavior in reptiles may be expressed with climbing or scratching at their glass tanks because they don't understand why they can't get out.
Other reptiles may become completely sedentary, seemingly sleeping their lives away behind a rock.
Creatures of the night cannot spend a day away from prying eyes.
Bears in zoos tend to bite, rub the mouth along the bars of the cage and even suck it.
This repetitive behavior can result in damage to the teeth and mouth, particularly if the bars are rusty.
Gorillas smearing faeces on walls and eat it.
Gorillas and chimpanzees vomit and then eat their vomit.
A zoo is a lunatic asylum.

Zoo babies are great crowd-pleasers, but what happens when an “exibt” loose its attraction? Zoos often sell or murder animals that no longer attract visitors. Some are murdered for their meat and their hides. Other "surplus" animals may be sold to smaller, poorer, zoos or to laboratories for experiments.
Deers, tigers, lions and other animals that breed often, are sometimes sold to "game farms” where hunters pay for the "privilege" of hunting them.

Zoos claim that they offer people the opportunity to see something that many will never see in the wild. The zoo people are right. They give us the opportunity to see what imprisonment does to animals. Most people don't see where the hens who laid their eggs live or how the pigs, that their bacons are made of, lived. But in zoos humans can see primates hide their faces, birds that don’t fly, mothers eat their young, elephants rock and swing for hours, bears and tigers pace all day long, monkeys stare, rhinos circle, anthropoid apes eat faeces and gorillas eat their own vomit. Still humans fail to see the boredom, the frustration, the madness and the suffer of caged animals. It is too natural for human to see animal in cages.

Some zoo workers believe that caging animals in a zoo, is some how for their own good. They want to protect the animals from harms. They see themselves as animal lovers and the zoo as a place that protects animals and enables people to get to know and love animals.

The confinement in the zoo harms animals more than anything they might face during their lives. Zoos cannot protect animals. In fact animals need protection from zoos.

Zoos also claim to be educational. But what do they teach us? Animals, which have become crazy and show unnatural stereotypic behavior are only 'educational' in showing how humans can drive animals mad by keeping them imprisoned.
The confinement educates people for relationships based on domination and control.
It teaches hierarchy and speciesism. It teaches how to objectify sentient creatures.
Not that humans need these lessons…

HUMANS ARE NATURAL BORN EXPLOITERS.