• Variation is all the differences which exist between members of the same species.
  • It is caused by a combination of genetic and environmental


Genetic variation refers to differences amongst organisms of the same species due to the differences in the genes they inherit from their parents. This is because they inherited different genes from their parents. Such variations can be inherited because they are genetically determined.


Environmental variation is variation due to the environment. Characteristics of animal and plant species can be affected by factors such as climate, diet, accidents, culture and lifestyle. A plant in the shade of a big tree will grow taller to reach more light.


There are two kinds of variation: continuous and discontinuous.


Continuous Variation

  • Continuous variation is variation that has no limit on the value that can occur within a population.
  • For any species, a characteristic that changes gradually over a range of values shows continuous variation. E.g.: height, weight, hand span.
  • This shape of graph is characteristic of a feature with continuous variation.
    continuous variation

Discontinuous Variation

  • Discontinuous variation is variation that has distinct groups for organisms to belong to.
  • A characteristic of any species with only a limited number of possible values shows discontinuous variation. E.g.: blood group, sex, eye color.
  • This graph shows discontinuous variation.
    discontinuous variation

Cause of Variation

  • Meiosis: during meiosis half of the chromosomes go into one gamete and half into the other gamete and half into the other gamete, each set of these chromosomes carries alleles with particular characters and this cause variation.
  • Fertilization: it’s a random process where one sperm from millions of sperms fuses with one ovum leading to the productions of certain characteristics which may be varied if another sperm fused with ovum.
  • Mutation: sudden change in the gene or chromosome.
  • Environmental factors: such as light, food.

Advantage of variation

  • Increases the chance of survival of the organism.
  • The nature alwaysselects the fittest organism.