Even though we have a brain that is a tad smaller than a human's, our brains are still very expanded and our heads and brains are actually bigger than our body mass. The highly social penguins need to understand each other and we've evolved complex languages.
There are claims that penguins are as intelligent as humans, if not more so.
We do have large brains for our body size, use language, and are easily trained by humans.

Penguins also learn very quickly and think quickly. Penguins can also recongize themselves in a mirror when first introduced to one and have a sense of self awareness. They also enjoy watching TV and respond to anything that moves on the screen right away. They can understand up to 300-500 english words and can learn what syntaxs are. They can communicate with people using sign language.

Man keeps thinking that we are the smartest, but in reality we are not. Think about it - animals that we come in contact with learn our commands - the only real commands we humans understand - but often do not obey is the command - keep away!!!