* Humans: We have the most complex brain of all animals, with billions of neurons.
* Mammals: All mammals have a relatively large and complex brain compared to other animals.
* Birds: Birds have a very small brain compared to mammals, but it's highly specialized for tasks like navigation and song learning.
* Fish: Fish brains are simpler than those of mammals and birds, but still perform essential functions.
* Insects: Insects have a simple brain structure called a "ganglion" which is located in their head.
It's important to note that even simple animals like insects have brains that are capable of complex behaviors, like navigating, finding food, and communicating.