How does evolution work?

Biological evolution is change in the genetic composition of populations over generations. It fundamentally requires variation among individuals, heredity (passing genes to offspring), and differential fitness. In practice, random mutations and recombination create genetic diversity; natural selection then favors alleles that boost survival or reproduction. When certain variants help individuals leave more offspring, those variants become more common. Over time this descent-with-modification process can lead to new species. Other forces like genetic drift and gene flow also alter allele frequencies. Put simply: populations inherit diverse traits, the environment "selects" the fitter ones, and genes shift accordingly – that is evolution in action.