Answer the following question given this paragraph: 

We see examples of mammals (other than people!) serving our needs everywhere. We have pets that are mammals, such as dogs and cats. Mammals are also used around the world for transport. For example, horses, donkeys, mules, or camels ( Figure below ) may be the primary means of transport in some parts of the world. Mammals also do work for us. Service dogs can be trained to help the disabled. These include guide dogs, which are assistance dogs trained to lead blind and visually impaired people around obstacles. Horses and elephants can carry heavy loads. Humans also use some mammals for food. For example, cows and goats are commonly raised for their milk and meat. Mammals’ more highly developed brains have made them ideal for use by scientists in studying such things as learning, as seen in maze studies of mice and rats.


Q: What broad group of animals - which includes rats, dogs and camels - have highly developed brains and often perform work for humans?


A:
mammals