11 Characteristics of Living Things

Defining "life" is a very difficult task, and scientists don’t all agree on a common list of the characteristics of life. Some of the other characteristics that the students may discover in their research, and which are often listed in textbooks, include those listed below. Many of these traits are not limited to living things. For example, fire uses energy, grows, and can reproduce, but it is not considered alive in part because it cannot evolve; its traits are necessary, but not sufficient, for life. NASA scientist Bruce Jakosky, in his book The Search for Life on Other Planets, provides a generally accepted definition of something being “alive” if it 1) utilizes energy from some source to drive chemical reactions, 2) is capable of reproduction, and 3) can undergo evolution.

Characteristics of Living Things

• All organisms use energy (metabolism).
• All organisms maintain a stable internal environment (homeostasis).
• All organisms detect and respond to select external stimuli.
• All organisms can engage in movement (which may occur internally, or even at the cellular level).
• All organisms show growth and development; that is, specialization of cells or structures. (Even unicellular organisms show a tiny amount of growth, and single cells repair and use materials from the environment to replace internal structures as needed.)
• All organisms reproduce. (Even if an individual can’t reproduce, its species can.) In addition, an individual’s cells are constantly reproducing themselves.
• All organisms have nucleic acid as the hereditary molecule.
• All organisms show adaptation, which occurs at the individual level and is tightly related to homeostasis.
• All organisms are made of one or more cells.
• All organisms exhibit complex organization, grouping molecules together to form cells; at a higher level, cells are organized into tissues, organs, and organ systems.
• All organisms exhibit evolution over time due to mutation and natural selection (which operates at the species level).