A pack animal is a type of animal used by humans to carry heavy loads. These animals carry goods and supplies upon their backs across long distances or difficult terrain.  

• They are not to be confused with draft animals, which pull weight on a cart or sled. The use of animals to carry cargo dates as far back as 3500 BC.  
• Historical evidence suggests that donkeys have served as pack animals for longer than any other species. Other types of common pack animals include camels, yaks, horses, llamas, oxen, and water buffalos.  

• Mules are preferred in the mountainous regions; while camels are used for caravan movement in deserts. In India, bullocks are used for pulling carts. 

Source: NCERT – XII Fundamental of Human Geography