Definition of the Theory of Evolution
The theory of evolution, primarily developed by Charles Darwin in the 19th century, posits that all species of life have descended from common ancestors through a process of gradual change over time. This change occurs primarily via natural selection, where individuals with advantageous traits are more likely to survive, reproduce, and pass those traits to offspring, leading to adaptations in populations.
Key Principles of Evolution
The theory rests on several core principles: variation among individuals in a population; heritability of traits; overproduction of offspring leading to competition for resources; and differential survival and reproduction favoring adaptive traits. These principles explain how species diversify and adapt to their environments without requiring purposeful design.
Evidence from the Fossil Record and Observations
A key example of supporting evidence is the fossil record, which shows transitional forms like Archaeopteryx, bridging reptiles and birds, illustrating gradual changes over millions of years. Modern observations, such as antibiotic resistance in bacteria, demonstrate evolution in real time, where populations adapt rapidly to selective pressures.
Additional Evidence and Broader Applications
Further evidence includes genetic similarities across species, such as shared DNA sequences between humans and chimpanzees (about 98-99%), and homologous structures like the pentadactyl limb in vertebrates. The theory underpins modern biology, informing fields like medicine (e.g., tracking viral evolution) and conservation (e.g., understanding species extinction risks), providing a unified framework for life's diversity.