It can be defined as the changes in the heritable characteristics of biological populations over successive generations.
The theory behind evolution is all species are related to one another and change with time gradually, it means species of plants, animals or insects slowly change their phenotype or physical characteristics.
These changes occur as a result of mutations or a change in the environment.
Every organism develops certain traits (as a result of this mutation or environmental change) that enable it to adapt to the altering surroundings.
Since these traits are favourable to the existence of these organisms, they are selected by nature and propagated to the future offspring.
These traits are engrained in the genotype of the organism.
The causes of evolution are natural selection,gene flow, genetic drift, mutation, and genetic recombination.