Definition of evolution and evolutionary theories

Definition of evolution – it is the gradual process by which living organisms change over time, involving heritable variation in traits, driven by mechanisms such as natural selection, mutation, genetic drift, and gene flow, which result in adaptation and sometimes in new species formation.

Darwin’s theory of natural selection – survival and reproduction of individuals with traits better suited to environment, leading to gradual change in population.

Lamarck’s theory of inheritance of acquired characters – traits developed during an organism’s life due to use or disuse of organs were believed to be passed to offspring, like giraffe’s neck getting longer due to stretching.

Mutation theory of De Vries – sudden, inheritable changes called mutations create new species without gradual change.

Modern synthetic theory – combination of Darwin’s selection with Mendelian genetics, incorporating gene mutation, recombination, genetic drift, migration, and isolation as driving forces of evolution.

Catastrophism – belief that earth’s history shaped by sudden, short-lived, violent events like floods or volcanic eruptions, followed by creation of new species.

Punctuated equilibrium – species remain stable for long periods, interrupted by short, rapid events of evolutionary change leading to new species.