What does the term 'evolution' refer to in a biological context?

In a biological context, 'evolution' refers to the cumulative change in heritable characteristics of a population over successive generations. This process arises through mechanisms such as natural selection, genetic drift, mutations, and gene flow. Heritable characteristics are traits that can be passed down from one generation to the next, and as these traits accumulate, they can lead to significant changes within a species, ultimately contributing to the diversity of life we observe.

Focusing on the cumulative aspect is essential because evolution is not just about a single change or event; it encompasses a long-term process where gradual modifications can significantly impact the species' genetic makeup over many generations. This includes changes in traits that may improve an organism's fitness in a given environment or lead to the emergence of new species through speciation.

The other options do not fully capture the essence of evolution. Change in environmental factors refers to external influences that may affect evolution but do not define it. Adaptation to climate is a specific outcome of evolutionary processes rather than a definition of evolution itself. Variation in species points to differences among individuals, which is a product of evolutionary processes but does not encapsulate the cumulative nature of heritable changes that drive evolution.