homeostasis that living things maintains a constant internal environment—was first suggested in the 19th century by French physiologist Claude Bernard, who stated that “all the vital mechanisms, varied as they are, have only one object: that of preserving constant the conditions of life.”

As originally conceived by Bernard, applied to the struggle of a single organism to survive.

All living organisms, regardless of their uniqueness, have certain biological, chemical, and physical characteristics in common. All, for example, are composed of basic units known as cells and of the same chemical substances, which, when analyzed, exhibit noteworthy similarities, even in such disparate organisms as bacteria and humans.