The primary driver of evolution in populations is natural selection. This process favors individuals with traits that enhance survival and reproductive success, allowing them to pass on their advantageous genes to the next generation. Over time, this leads to a shift in the genetic composition of populations as beneficial traits become more common. Other factors, such as genetic drift and gene flow, also influence evolution, but natural selection is the principal mechanism driving adaptation and speciation, fundamentally shaping the course of life on Earth.