Variation

Variation in biology means the differences between organisms in a species. These differences can be observed in how they appear, how their bodies function, or how they behave. For example, variation in the human species includes differences in height, skin color, eye color, and blood type.

No two individuals are exactly the same. Variation is important for the study of genetics, evolution, and populations.

There are two main causes for variation: genetics and the environment.

Sources of variation

Genetic variation

This is a variation in the DNA of individuals. It is heritable, which means it can be passed from parents to their children. Genetic variation is the basis of evolution. It comes from two main sources:

• Mixing genes: In sexual reproduction, an offspring gets a unique mix of genes from both parents. The shuffling of genes creates new combinations of traits. This is why children look a bit like their parents but are not identical to them.

• Mutation: A mutation is a permanent change in the DNA. Mutations are the source of all new genetic traits. Most mutations have no effect or are harmful, but some can cause a new, helpful trait to appear.

Environmental variation

These are differences caused by an organism's life and surroundings, not by its genes. This kind of variation is not passed down to the children.

For example, a plant with genes to be tall might not grow tall if it does not get enough water, sun, and food. A person who exercises a lot will build muscle, but their children will not be born with large muscles.

Why variation is important

Variation is necessary for evolution by natural selection.

Natural selection is the process by which living things with beneficial traits are more likely to survive and have offspring. For this to happen, there must be a variety of traits to "select" from. Variation provides this variety.

White-bodied peppered moth

Black-bodied peppered moth

A famous example is the peppered moth:

1. In England, most peppered moths were light-colored, which camouflaged them on light-colored trees. A few had a mutation that made them dark-colored.
2. When factories made the trees dark with soot, the light moths were easy for birds to see and eat.
3. The dark moths, however, were now camouflaged. They survived better and had more babies.
4. Over time, most of the moths in the population became dark.

If there had been no dark moths (no variation), the species might have died out when the environment changed.