The term "rhythm", taken from the Greek "ῥυθμός" - "rhythmos", designates any kind of regular and recurrent symmetrical motion. It could also be described as an orderly succession of regulated movements, of both weak and strong elements. Many cyclical natural phenomena can be said to possess this kind of general time and recurrence pattern. Starting from microseconds to millions of years, most anything can be measured by periodicity or frequency.
Rhythm occurs of course in the performance arts. There, it represents the way events are timed on our human scale. Musical sounds and silences are also timed by rhythm, as well as the steps of a certain dance or the meters of poetry or mostly any kind of spoken language. Visual presentation can be referred to by rhythm as a sort of time-measured space movement. Many scholars have recently initiated researches on the subject of rhythm and musical meter. In this respect, we could mention books written by Maury Yeston, Jonathan Kramer, Christopher Hasty, William Rothstein, Joel Lester, Fred Lerdahl and Ray Jackendoff.
In his well-known work entitled "Arbeit und Rhythmus", Bücher writes about his having reached the conclusion "that while in the first stages of their development labor, music and poetry were usually blended, labor was the predominant element, the others being only of secondary importance." He also explains that labor is actually the true origin of poetry. Indeed, if we consider the sounds and breathing exercises primitive people made as they worked, we could say that labor indeed may have represented a primitive form of singing and dancing.
However, rhythm could not possibly be enough to explain the complexity of music and dance. Rhythm is likely to provide the framework, the articulation, the connecting principle. Nonetheless, rhythm needs to give shape to a certain sensorial matter. It can turn the musical phrase into something unified and individual, it may confer value and importance to the succession of sounds. In a way, we may say that rhythm is actually the string that bears the diversely-colored, shaped and sized beads. Indeed, rhythm needs to assemble all these sensitive values.
Rhythm is a deep function that governs all our forms of perception and movement. Some say that there isn't any such thing as a musical rhythm. However, there isn't any rhythm that could not actually be part of a musical form. That is why rhythm has so much power. it introduces in music the very life of psychological states of mind. Both intellectually and effectively, rhythm introduces the entire rich variety full of nuances of the emotions and intellectual moods; it is in fact the diverse order of thinking and feelings.
The chief conductor imposes his rhythm to his orchestra. According to Henri Delacroix, a conductor can invest time with rhythm. He is at the same time the mime and the dancer of the music performed at his very own command. A conductor's entire body actually reproduces rhythm. With one hand, he reproduces time and strength; with the other hand, the traits of grace and mildness; in his muscles various spirits spread out which within music are mixed and agitated. The conductor imposes his text upon his instrument players, and at the same time translates this text to the great audience, which can follow the movement of his arms and of his shoulders. So the conductor has the task to direct both his listeners and his musicians towards the musical realm.
Howard Goodall explains in his series entitled How Music Works Howard Goodall, certain theories according to which human rhythm actually reminds us of the mother's heartbeat heard in the womb, or of the regular steps we take as we walk. Also, London says that musical meter is related to our initial perception as well as to the following anticipation of some beats that we get abstracted from the music's rhythm surface as it displays itself in time. According to neurologist Oliver Sacks, chimpanzees or other animals are not endowed with this sense of rhythm. However, in the case of humans this sense is fundamental, and can by no means be lost by accident. He also adds that the human rhythmical performance arts could have their roots in some ancient courtship rituals.