Short answers, pulled from the story.
Negative feedback occurs when some function of a system's output is fed back in a way that reduces fluctuations, whether caused by changes in input or by other disturbances. It works by measuring the difference between a desired value and the actual value, then applying a correction that narrows that gap, promoting stability and equilibrium.
Harold Stephen Black invented the negative feedback amplifier at Bell Laboratories in 1927. He submitted a patent application in 1928 and published a detailed paper in 1934. The patent, US Patent 2,102,671, was granted in 1937 and ran to 52 pages plus 35 pages of figures.
Negative feedback in biology includes the baroreflex that regulates blood pressure, the hormonal cascade controlling glucocorticoid secretion through the hypothalamus, pituitary gland, and adrenal cortex, and the regulation of blood glucose levels. When the glucose feedback loop fails, it can result in diabetes.
Self-regulating mechanisms based on negative feedback were in use as early as 200 BCE, when Ktesibios of Alexandria refined water clocks to maintain a constant reservoir level. Cornelius Drebbel built thermostatically controlled incubators and ovens in the early 1600s, and James Watt patented a centrifugal governor for his steam engine in 1788.
Negative feedback loops can oscillate because of phase shifts around the loop. At certain frequencies, the phase shift reaches 180 degrees, causing the corrective signal to arrive back in phase with the original disturbance and turning negative feedback into positive feedback. Engineers address this through compensation, low-pass filters, or dampers.
In climate systems, negative feedback stabilizes temperature through loops involving solar radiation, cloud cover, and albedo. When solar radiation increases and raises planet temperature, plant growth and water vapor production increase, which generates more cloud cover, which reflects more solar radiation and reduces temperature. These loops counteract disturbances rather than amplify them.