Living things perpetuate their species by reproduction. The asexual method is not a common process in organisms. Certain very primitive forms of life multiply by this method which is also known as fission. In humans, as in all higher forms of life, the sexual method or union of two sex cells (known as gametes) is the method of reproduction. The male and female gametes are symbolically designated as male or female. These gametes are produced in gonads. The union of the male sperm with the female ovum is known as fertilization. Other functions of the gonads are to produce the male and female sex characteristics, such as voice, shape, bone structure, distribution of body hair, etc.