A general label covering all periods of biological
systems. The most intensely studied are the circadian rhythms, although many
biological functions show a period other than a daily one, for example,
menstrual cycles, bird migrations, protective-coloring changes, etc. Note that
in recent years this term has become "contaminated" by the emergence of a
pseudoscience of the same name. Using the so-called biorhythm methods its
practitioners claim to be able to predict a person's performance on a task on
any given day, on the basis of a chart of their biorhythms from their day of
birth. An utter lack of supportive evidence for these claims has, predictably,
had little impact on public acceptance but it has led scientific researchers to
cast about for a new label for their field.