The fossil record serves as one of the strongest pieces of evidence supporting the theory of evolution. Fossils are the preserved remains, impressions, or traces of organisms that lived in the past and are typically found in sedimentary rock layers. By studying fossils from different geological periods, scientists can observe how organisms have changed over millions of years. Older rock layers generally contain simpler and more primitive organisms, while younger layers contain more complex and modern forms. Transitional fossils, such as those showing characteristics of both ancestral and descendant groups, provide direct evidence of gradual evolutionary change. Examples include fossils that reveal the evolution of fish into amphibians, reptiles into birds, and land mammals into whales. Through the fossil record, scientists can reconstruct the history of life on Earth and trace the development, diversification, and extinction of species over time. This evidence demonstrates that organisms are not fixed but have evolved in response to environmental changes and natural selection. 

The geographical distribution of organisms, known as biogeography, provides compelling evidence for evolution. Scientists have observed that species living in different regions often share similarities with nearby species rather than with species living in similar environments elsewhere. This pattern suggests that species evolved from common ancestors and adapted to local conditions over time. For example, the unique species found on islands, such as those in the Galápagos Islands, closely resemble species from the nearest mainland but have developed distinct characteristics suited to their specific environments. Continental drift and the movement of tectonic plates have also influenced species distribution by separating populations and allowing them to evolve independently. The presence of related species on different continents, despite geographical barriers, supports the idea that these species descended from common ancestors before landmasses became separated. Biogeography helps explain how environmental pressures, isolation, migration, and adaptation contribute to the formation of new species and the diversity of life observed today. 

Comparative anatomy and molecular biology provide strong evidence for common ancestry among living organisms. Comparative anatomy involves examining similarities and differences in the physical structures of different species. Homologous structures, such as the forelimbs of humans, bats, whales, and cats, have similar underlying bone arrangements despite serving different functions. These similarities indicate that the species inherited these structures from a common ancestor. Vestigial structures, such as the human appendix or whale pelvic bones, further support evolutionary change because they are remnants of features that were functional in ancestral organisms. Molecular evidence, including DNA and protein comparisons, offers even stronger support for evolution. Organisms with similar DNA sequences are generally more closely related than those with greater genetic differences. Scientists can compare genes and proteins among species to determine evolutionary relationships and construct phylogenetic trees that illustrate patterns of descent. Together, comparative anatomy and molecular evidence reveal that all living organisms are connected through evolutionary history and share common ancestors.