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In biology, evolution is the accumulation of genetic changes in a population over successive generations. These changes arise from alterations in the DNA sequence—new genes, novel traits, and eventually new species. Among the mechanisms that generate evolutionary change, natural selection is the most powerful force that shapes the diversity of life.
During cell division, DNA is copied by the replication machinery. Although the process is remarkably accurate, errors do occur, producing mutations in one or both daughter cells. These genetic alterations create the raw material for variation within a population. Even organisms that share a common ancestry display distinct DNA sequences because mutations, coupled with sexual reproduction, continually generate diversity.
When environmental conditions favor certain traits, individuals possessing those traits tend to survive longer and reproduce more successfully. The advantageous mutations they carry become more prevalent in the gene pool over time, while deleterious mutations decline. This differential reproductive success is the essence of natural selection, the engine that drives adaptive evolution.
A genotype represents the complete set of genetic variants an organism holds, whereas a phenotype is the observable manifestation of those genes—eye color, height, and other traits. Environmental influences can modify the phenotype, meaning the same genotype may produce different traits under varying conditions. Because natural selection acts on phenotypic performance, it indirectly favors certain genotypes.
Over long periods, a highly advantageous allele can become fixed, meaning all individuals in the population carry it while other variants disappear. However, many alleles confer only marginal benefits or none at all, allowing multiple variants to coexist. This balance preserves genetic diversity, which is vital for future adaptability.
