Sentence:  Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to kindle a flame. With more settled people, <WSD>animals</WSD> were harnessed to capstans or caged in treadmills to turn grist into meal. 
Meaning of the word marked with <WSD> tags:  In non-scientific usage, any land-living (vertebrate) (i.e. not (fishes), (insects), etc.).