While Darwin proposed the theory of natural selection based on observations, he lacked a mechanism for how traits were inherited.
The later discovery of Mendelian genetics and the structure of DNA in the 20th century provided the missing link, explaining how genes carry information and how mutations create the variation necessary for selection.
Modern gene theory confirms that characteristics are passed via alleles, and the frequency of these alleles changes in a population over time in response to environmental pressures.
Extinction occurs when a species fails to adapt to environmental changes, such as new predators, diseases, or catastrophic climate shifts, resulting in the death of all remaining individuals.
Evolutionary trees are used to visualize the relationships between species; each branch point represents a common ancestor from which two or more species diverged.
By comparing the DNA and physical structures of living species and fossils, scientists can determine how recently two species shared a common ancestor, indicating their degree of relatedness.
Identify the Mechanism: When asked about bacterial resistance, always mention that the mutation occurs randomly before the antibiotic is applied, not in response to it.
Explain the Gap: If a question asks why we lack evidence for early life, focus on the lack of hard parts (soft-bodied organisms) and the destruction of traces by geological activity.
Interpreting Trees: Remember that the closer the branch point (node) is to the present day, the more closely related the two species are.
Common Error: Do not say that an individual organism 'evolves' to survive; instead, state that the population evolves as advantageous alleles are passed on by surviving individuals.
