In contrast to genetic drift, natural selection is not a random process because it acts on traits that are necessary for survival and reproduction.
The modern understanding of evolution began with the 1859 publication of Charles Darwin's On the Origin of Species.
The majority of genetic mutations neither assist, change the appearance of, nor bring harm to individuals.
Through the process of genetic drift, these mutated genes are neutrally sorted among populations and survive across generations by chance alone.
Darwin gained extensive experience as he collected and studied the natural history of life forms from distant places.
Based on the similarities between all present-day organisms, all life on Earth is assumed to have originated through common descent from a last universal ancestor from which all known species have diverged through the process of evolution.
The forces of evolution are most evident when populations become isolated, either through geographic distance or by other mechanisms that prevent genetic exchange.
Over time, isolated populations can branch off into new species.
These differences accumulate resulting in changes within the population.
This process is responsible for the many diverse life forms in the world.