<span>By allowing the ground to grow fallow, it absorbs, through rain and natural means the nitrogen and phosphorus necessary in order to fertilize plants. Then once the field is plowed, the elements mix together to form the foundation by which the seeds can be nurtured and grow more effectively.</span>
It reproduce by a process call Binary Fission
Humans can will themselves to eat more, as we know that food comes easy to us.
Animals, on the other hand, top priority is survival, so they usually wouldn't think about eating more because it just "tastes good."