Life is a biological concept regarding the characteristic state of organisms that have the capacity to perform various functions, including metabolic processes, self-replication, and responsiveness to stimuli. The science of biology studies life from many perspectives, including those of molecular biology, biochemistry, ecology, evolution, and taxonomy.
The word “life” comes from the Proto-Indo-European root *lei-, meaning “to flow”. This root has given rise to other words in English with related meanings, such as liveliness and livelily. The concept of “life” has been one of the central topics in philosophy since antiquity. Aristotle defined it as the activity characteristic of all organisms (including plants) that involves maintenance of homeostasis, regulation of growth and development, response to stimuli, and reproduction. In contrast to Aristotle’s definition based on function), modern biologists define life more flexibly: Charles Darwin stated that “it is not easy to define what we mean by life”, while François Jacob described life simply as information capable of self-replication.
In general terms, there are three major defines what is considered “alive”: metabolism—the sum total of an organism’s chemical reactions; irritability or responsiveness—the ability to detect changes in its environment and respond accordingly; and reproduction—the ability to produce offspring identical or nearly identical to itself. Although these criteria are sufficient for most practical purposes (e.g., distinguishing between a rock and a bacterium), they leave out important phenomena such as consciousness and sentience (which some people consider crucial features of “aliveness”). Furthermore, different scientists may have different opinions on which criteria are most important; for example,…