In 'Animal Farm' the pigs are considered to be clever because they can read. They also demonstrate other leadership abilities needed to run the farm. For example, some farm implements have to be modified to be used by animals instead of humans. Snowball even draws up a blueprint for a windmill to produce electricity.
The pigs are also able to think in abstraction and ideals. Of all the farm animals, it is Snowball and Napoleon who formulate the concept of "Animalism" and set up the Seven Commandments.
Another aspect of their intelligence comes to the fore later on with Napoleon's craftiness. He takes Bluebell's puppies away to be trained as his secret police and he recruits Squealer as his "middle man" and representative. A pig himself, Squealer proves to be an excellent orator can persuade the animals every time to come around to his point of view. It is said that Squealer can turn 'white' to 'black' and 'black' to 'white.' The pigs are not only apt leaders but excellent manipulators as well.
In this political allegory as in the upheaval of the Russian Revolution and its aftermath, these aspects make the distinction between those who seize power and take control and those who are subjugated.
In Animal Farm, The Pigs could represent clever, educated people and the other animals could represent normal working people.
Animal Farm is about Communism. Communism assumes that everyone is completely equal. It trys to build a totally equal society. But people (or animals) are not equal. The pigs are more intelligent than the others. The animals are not all the same. So the pigs use their intelligence to take all the advantages, power, priviledges etc.
Orwell is trying to say that people will naturally try to gain more for themselves. He's saying we are selfish and that the more intelligent members of a society (pigs) will be more succesful and grabbing everything.