Life Cycle

∞ generated and posted on 2020.09.24 ∞

Passage of an organism from "birth" through birth of equivalent offspring.

"Birth" is in quotes because I am not using the usual, narrow definition of the term, meaning to exit in an immature state from one's mother's womb, but instead in the sense of an organism starting out its life at some immature, semi-independent-from-one's-parent stage. This thus could be at the point of hatching, or seed dispersal, or even the conclusion of binary fission. A life cycle thus passes, for example, from an individual's start in life that start through to the next generation's equivalent start.

A life cycle can start at any specific point in an organism's existence and then end at any specific but nevertheless consistent point in the existence of that organism's offspring, and thus need not be limited solely to going from birth to birth. Focus in considering life cycles, however, typically is on a combination of what it takes for an organism to reach reproductive maturity and then how reproduction takes place.

This focus generally will be the case regardless of whether an organism's reproduction is sexual or instead asexual. With sexual organisms, however, an important part of the life cycle will be finding a mate.

A life cycle generally takes at least one 'generation time' to complete and results in the generation of progeny individuals, though can certainly encompass iteroparity, i.e., the production of more than one batch (or clutch) of offspring per lifetime.

At least so long as different generations retain the same ploidy, if not necessarily always the same morphology or even environment, then we can describe each generation as progressing through a single life cycle. Note, however, that a number of organisms pass through different stages of ploidy that represent different generations – as most notably seen with alternation of generations in plants – but a life cycle most reasonably starts and ends at the same point in the same stage.

The term "life history" may be employed to take into account the different stages that an organism can display over the course of its life cycle.