Natural selection favors individuals with heritable traits that enhance survival and reproduction, driving progressive adaptation over generations. Other processes contribute to genetic change but do not directly select for beneficial traits in the same systematic way.

Genetic variation refers to the differences in the DNA sequences among individuals in a population. This variation is essential for natural selection to act upon, leading to evolutionary change over time.

An adaptation is a heritable trait that enhances an organism's ability to survive and reproduce in its environment. It results from the selective pressures exerted by natural selection over many generations.

Fossil records depict gradual changes in organism structures over immense time spans, providing robust evidence for the process of evolution. They showcase transitional forms that link ancestral species with modern descendants.

The phrase 'survival of the fittest' is used to describe how individuals with traits suited for their environment tend to have higher survival and reproductive success. It does not imply physical strength alone, but rather overall suitability to environmental challenges.

Mutations are changes in the DNA that create new genetic variations, which are the raw material for evolution. Although not every mutation is beneficial, some may enhance survival and reproduction when environmental conditions favor them.

Gene flow involves the transfer of genetic material between distinct populations, often via migration. This process increases genetic diversity and can introduce alleles that may be beneficial in a new environment.

Convergent evolution occurs when unrelated species develop similar traits because they face similar environmental challenges. Dolphins and sharks, though from different lineages, have evolved streamlined bodies for efficient swimming.

Genetic drift is particularly significant in small populations where random events can lead to substantial changes in allele frequencies over time. In larger populations, the effect of drift is diluted by the sheer number of individuals.

Allopatric speciation occurs when populations are geographically isolated, preventing gene flow between them. This separation allows distinct genetic differences to arise over time, potentially leading to the formation of a new species.

Natural selection promotes the spread of alleles that confer an advantage in survival and reproduction. Over generations, this selective pressure increases the prevalence of beneficial traits within a population.

Sexual selection is a form of natural selection where traits that enhance an individual's ability to attract a mate become more prevalent. This process can lead to the development of features that may not necessarily improve survival but increase reproductive success.

Nearly all living organisms use the same genetic code, which is strong evidence for a common ancestral origin. This universality links the diverse forms of life on Earth together through a shared evolutionary heritage.

Climate stability implies a lack of significant environmental pressures, making it less likely to drive evolutionary change. In contrast, mutations, natural selection, and genetic drift actively influence how species evolve.

Transitional fossils exhibit characteristics that are intermediate between those of ancestral and descendant groups. They provide crucial evidence for the gradual process of evolution by illustrating the passage from one form to another.

Coevolution involves reciprocal evolutionary changes between interacting species, such as predators and their prey. This dynamic relationship drives adaptations in both parties, illustrating the interconnected nature of evolutionary processes.

Genetic drift refers to random fluctuations in allele frequencies, particularly in small populations. This process can lead to the fixation of alleles irrespective of their impact on fitness, including those that are neutral or disadvantageous.

Epigenetics involves modifications that affect gene expression without changing the underlying DNA sequence. These heritable alterations add a complex layer to traditional genetic inheritance, influencing evolutionary outcomes beyond classic mutations.

Molecular clocks utilize the steady rate of genetic mutations to estimate when two species diverged from a common ancestor. This method provides a timeline for evolutionary events and helps validate fossil records.

Horizontal gene transfer involves the exchange of genetic material between unrelated species, which can obscure traditional lineage relationships. This process challenges the simple, branching tree model of evolution by adding networks of gene sharing.