process by which organisms replicate themselves.
             In a general sense reproduction is one of the most important concepts in biology: it means
             making a copy, a likeness, and thereby providing for the continued existence of species.
             Although reproduction is often considered solely in terms of the production of offspring in
             animals and plants, the more general meaning has far greater significance to living organisms.
             To appreciate this fact, the origin of life and the evolution of organisms must be considered.
             One of the first characteristics of life that emerged in primeval times must have been the ability
             of some primitive chemical system to make copies of itself.
             At its lowest level, therefore, reproduction is chemical replication. As evolution progressed, cells
             of successively higher levels of complexity must have arisen, and it was absolutely essential
             that they had the ability to make likenesses of themselves. In unicellular organisms, the ability
             of one cell to reproduce itself means the reproduction of a new individual; in multicellular
             organisms, however, it means growth and regeneration. Multicellular organisms also reproduce
             in the strict sense of the term--that is, they make copies of themselves in the form of
             offspring--but they do so in a variety of ways, many involving complex organs and elaborate
             In single-celled organisms (e.g., bacteria, protozoans, many algae, and some fungi),
             organismic and cell reproduction are synonymous, for the cell is the whole organism. Details of
             the process differ greatly from one form to the next and, if the higher ciliate protozoans are
             included, can be extraordinarily complex. It is possible for reproduction to be asexual, by
             simple division, or sexual. In sexual unicellular organisms the gametes can be produced by
             division (often multiple fission, as in numerous algae) or, as in yeasts, by the organism turning
             itself into a game...