ABSTRACT
Although life as a biological process remains mysterious and miraculous, the requirements for maintaining life over time are remarkably simple: Organisms must “eat, retreat, and excrete.” Stated more formally, they must be able to: (a) procure nourishment; (b) resist external threats; and (c) dispose of internal threats. Among single-celled animal life such as amoebas, these three basic life requirements manifest, respectively, as (a) surrounding and appropriating a food source (engulfment); (b) repelling and/or eluding predators, parasites, and contaminants, as well as encysted dormancy during periods of prolonged environmental adversity (resistance); and (c) eliminating toxic metabolic by-products and any other threats that have become internalized (excretion).
