Int. J. Environ. Res. Public Health 2010, 7 940 2. Periodicity as a Common Feature of Numerous Biological Processes and Nature of Corresponding Regulatory Influences Life entails a spectrum of natural rhythms. Periodicity is a typical feature of numerous biological processes and life itself on various levels of its organization: subcellular and cellular (segmentation clock, cell cycle, transcription factors’ activity oscillations, etc.) [2-4], tissue and organ (oscillations in electrical activity of the brain, heartbeats), organism (circadian rhythms) [5,6], in populations of organisms and in Biosphere (seasonal changes, etc.). Some authors have collected evidence of “Solar-dependent” rhythm in biological processes [7-10]. In 1936, A. Chizhevsky concluded: “Life is a phenomenon… It lives due to dynamics; each oscillation of organic pulsation is coordinated with the cosmic heart in a grandiose Whole of nebulas, stars, the sun and the planet.” [1]. There is evidence that some epidemic processes have rhythmic nature as well [11,12]. It is possible to notice periodicity in influenza epidemic occurrence. For example, E.D. Kilbourne reported a 10−11 year periodicity in the occurrence of influenza pandemics and proposed that this is due to a periodicity in antigenic shifts [13]. R.E. Hope-Simpson noted coincidences between flu pandemics and maxima of solar activity, which occur with an approximately 11-year period [14]. These observations were continued, developed and statistically tested later on [15-17]. Do there exist any universal mechanisms able to drive and regulate this biological and Biosphere periodicity in its numerous manifestations? To answer this question, let us recognize some characteristic elements of biological periodic processes in general. Machinery of many periodic processes includes several typical components, among them: - pacemaker; - regulatory signals emitted by pacemaker; - receptors of the regulatory signals in the controlled constituent. A review of modern biomedical knowledge shows that regulatory signals in many known biological processes are of an electromagnetic nature: heartbeat, breathing, peristaltic motions of guts – all these manifestations of life exist due to transmittance of electrical and chemical signals in corresponding neuronal chains. Among less evident regulatory functions of the electromagnetic fields (EMF), there are the direction of cell differentiation [18], regulation of the orientation and frequency of cell division and wound healing rate, control of nerve growth and cell migration [19], among others. The BioInitiative Report [20] contains a reasonable statement: “Human beings are bioelectrical systems. Our hearts and brains are regulated by internal bioelectrical signals”. At the same time, our environment is permeated by EMFs of natural and artificial origin. The main sources of the natural EMFs are atmospheric electricity, the Earth’s magnetic field and its occasional perturbations caused by interaction between the geomagnetic field and solar wind plasma. Environmental exposures to EMFs can interact with fundamental biological processes and there may be no lower limit at which EMF exposures affect us [21]. Such an important and universal role of electromagnetic interactions in biology is not unexpected since there are four known types of interactions in nature of which only two can exercise effects over a distance that exceeds the dimension of an atomic nucleus. Mentioned “long-distance” interactions are Gravity and Electromagnetic (EM) interactions, and there are no others. It is the basic reason