Because of the myriad genes in the nucleus of every parent cell,
the probability of two individuals inheriting identical
characteristics is almost zero; thus, innumerable new variations
(see mutation) constantly undergo testing for survival
advantages in the individual's environment. The evolutionary
flexibility that results from sexuality at some stage of the
reproductive cycle seems not only beneficial but necessary in
maintaining the adaptability of the species. The Human Genome
Project is mapping and sequencing the approximately 30,000 human
genes. The goal of this international scientific effort focuses
on discovering the genetic basis for diseases in order to help
humans avoid having children with severe or fatal genetic
disorders. Sections in this article: