Multiple lines of evidence support evolution, including the fossil record, which shows chronological changes in life forms; comparative anatomy, such as homologous, analogous, and vestigial structures; molecular biology, like DNA sequencing and molecular clocks; biogeography, the geographic distribution of species; and embryology, which reveals developmental similarities across species. These diverse sources collectively corroborate evolutionary theory.

Homologous structures are body parts that share a common ancestry but may perform different functions, such as the forelimbs of humans, whales, and bats. Analogous structures are those that have similar functions but evolved independently, like the wings of insects and birds. The distinction helps scientists infer evolutionary relationships versus convergent adaptations.

Genetic drift causes random changes in allele frequencies within a population, and its effects are more pronounced in small populations where genetic variation is limited. It can lead to the loss of alleles or the fixation of new ones by chance events, examples being the bottleneck effect, such as in the northern elephant seal, and the founder effect, like in Amish populations. This mechanism can reduce genetic diversity and shape the evolutionary trajectory of isolated groups.

Antibiotic resistance arises when bacteria with mutations that confer resistance survive antibiotic treatment and reproduce, passing the resistant traits to subsequent generations. The overuse of antibiotics creates selective pressure that increases the frequency of resistant strains, making infections harder to treat. Understanding this evolutionary process highlights the need for prudent antibiotic use and the development of new drugs.

Evolution is a core component of the SAT science section, as it underpins many biological concepts tested on the exam. A solid grasp of evolutionary principles helps students answer questions about natural selection, adaptation, and the relationships between organisms. Mastering this topic is essential for achieving a high score on the SAT and for success in college-level biology courses.