Sleep is the state of rest of the brain and body where physiological processes take place. More observably, the eyes close and the brain enters into a state of unconsciousness, either completely or partially. Moreover, sleep is guided by sleep/wake cycles and circadian rhythm.
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Closely packed is like a sheet layer
Allele frequencies in a population may change due to four fundamental forces of evolution: Natural Selection, Genetic Drift, Mutations and Gene Flow. Mutations are the ultimate source of new alleles in a gene pool. Two of the most relevant mechanisms of evolutionary change are: Natural Selection and Genetic Drift.
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what is the question??? I can't understand it sorry