Human evolution depends on the variations in our DNA and on our capacity to pass on these variations to future generations (i.e., our breeding capacities). As these variations become more noticeable over time, the population should shift. A new species will develop if there are significant enough genetic alterations. Variation, natural selection, and geographic isolation—the three elements necessary for evolution to take place—have all but been eliminated from the equation. The world's population is mingling and no longer merely breeding within cultural or ethnic groups; rather, humans might be thought of as a single genetic "continent." It is hypothesised that, through time, humans will begin to resemble one another more and more, eventually achieving the "average" of all current physical variations.

The genetic material—the chemical molecule, DNA—that is inherited from the parents changes throughout time, and this is especially true of the ratios of various genes in a population. Genes are the sections of DNA that contain the chemical instructions needed to make proteins. Mutation is the process through which the DNA's information can alter. Particular genes' expression, or how they affect an organism's structure or behaviour, can also alter. Genetically inherited traits can affect the likelihood of an organism's survival and reproduction because genes determine how the body and behaviour of an organism evolve over its existence.

Modern people have developed from earlier humans, as demonstrated by fossils like those in our Human Fossils Gallery. These skulls keep track of changes in traits including face and brain size and form. Other fossils demonstrate how the skeleton has evolved during the last 6 million years.