[Alstrom, K.J., Murray, R.M., Feedback Systems: An Introduction for Scientists and Engineers, 2006.]
Feedback is a central feature of life. The process of feedback governs how we grow, respond to stress and challenge, and regulate factors such as body temperature, blood pressure, and cholesterol level. The mechanisms operate at every level, from the interaction of proteins in cells to the interaction of organisms in complex ecologies.
[Mahlon B. Hoagland and B. Dodson, The Way Life Works, 1995]