Variation Within Species
1. What Is Variation?
Learning outcomes
- I can define variation within a species.
- I can identify examples of variation in populations.
- I can explain why individuals within a species are not identical.
- I can distinguish between inherited and acquired characteristics.
- I can describe the importance of variation for survival.
Introduction
Look around any classroom, sports team, or family. Although everyone belongs to the same species, no two people are exactly alike. Some people are taller, some have curly hair, others have different eye colours, fingerprints, or blood groups. These differences are examples of variation.
Variation occurs in every species on Earth, from plants and animals to bacteria. It is one of the most important features of living organisms because it allows populations to adapt to changing environments over time. Without variation, species would struggle to survive environmental changes, diseases, and other challenges.
What Is Variation?
Variation refers to the differences in characteristics between individuals of the same species.
Characteristics that can vary include:
- Height.
- Hair colour.
- Eye colour.
- Blood group.
- Leaf shape.
- Flower colour.
- Fur pattern.
Variation means that no two individuals are exactly the same (except identical twins, which are genetically almost identical).
Figure 1. Individuals within the same species show many different forms of variation.
Variation Within a Population
A population is a group of individuals of the same species living in the same area.
Within a population, individuals may differ in:
- Size.
- Colour.
- Behaviour.
- Speed.
- Disease resistance.
- Ability to tolerate different environmental conditions.
For example:
A population of rabbits may include individuals with:
- White fur.
- Brown fur.
- Larger ears.
- Smaller ears.
- Different body sizes.
These differences are examples of variation.
Why Are Individuals Different?
Individuals are not identical because of two main factors:
- Genetics (inheritance).
- Environmental influences.
Many characteristics are affected by both.
For example:
Height depends on:
- The genes inherited from parents.
- Nutrition and overall health during growth.
Inherited Characteristics
Inherited characteristics are passed from parents to offspring through genes.
Examples include:
- Eye colour.
- Natural hair colour.
- Blood group.
- Attached or detached earlobes.
- Ability to roll the tongue (in some genetics models).
These characteristics are determined mainly by DNA.
They cannot usually be changed by lifestyle or experience.
Figure 2. Inherited characteristics are passed from parents to offspring through genes.
Acquired Characteristics
Acquired characteristics develop during an individual's lifetime.
They are caused by:
- Lifestyle.
- Environment.
- Learning.
- Injury.
- Experience.
Examples include:
- A suntan.
- Muscle development from exercise.
- Scars.
- Pierced ears.
- Learning a new language.
These characteristics are not passed on genetically to offspring.
Comparing Inherited and Acquired Characteristics
| Inherited Characteristics | Acquired Characteristics |
|---|---|
| Passed from parents | Develop during life |
| Controlled mainly by genes. | Influenced by the environment or experience |
| Usually permanent | May be temporary or permanent |
| Passed to offspring | Not inherited by offspring |
Understanding this difference is essential in genetics.
Figure 3. Inherited characteristics come from genes, while acquired characteristics develop through life experiences and environmental influences.
Continuous and Discontinuous Variation
Variation can be grouped into two broad categories.
Continuous Variation
Characteristics show a range of values.
Examples include:
- Height.
- Body mass.
- Hand span.
- Foot length.
There are many possible values with no clear groups.
Discontinuous Variation
Characteristics fall into distinct categories.
Examples include:
- Blood group.
- Natural eye colour categories.
- Ability to roll the tongue (in simplified genetics examples).
Individuals belong to one category or another, with no intermediate values.
Why Variation Is Important
Variation is essential because it helps populations survive when environments change.
For example:
If a disease affects a population:
- Some individuals may be naturally resistant.
- These individuals survive and reproduce.
- Their offspring may inherit the resistant characteristics.
Variation therefore increases the chances that a species will continue to exist.
Figure 4. Variation increases the likelihood that some individuals will survive changing environmental conditions.
Examples of Variation in Nature
Variation can be seen throughout the natural world.
Examples include:
- Different flower colours in the same plant species.
- Different fur colours in wolves.
- Different beak sizes in birds.
- Different shell patterns in snails.
- Different leaf shapes within a tree species.
Every population contains natural variation.
Variation and Evolution
Variation provides the raw material for evolution.
Natural selection acts on variation by favouring individuals with characteristics that improve survival and reproduction.
Over many generations:
- Helpful inherited characteristics become more common.
- Populations gradually change.
Without variation, evolution could not occur.
Why Scientists Study Variation
Scientists study variation to:
- Understand inheritance.
- Improve crop plants.
- Breed healthier livestock.
- Develop medicines.
- Protect endangered species.
- Investigate evolution.
Variation is one of the central ideas in biology.
Figure 5. Variation occurs in all living organisms and is fundamental to genetics and evolution.
Worked Example
Question
Classify each characteristic as inherited or acquired.
- Eye colour
- Scar from a bicycle accident
- Blood group
- Suntan
- Muscle growth from exercise
Solution
| Characteristic. | Type |
|---|---|
| Eye colour | Inherited |
| Scar | Acquired |
| Blood group | Inherited |
| Suntan | Acquired |
| Muscle growth | Acquired |
Real-World Connection
Plant breeders make use of natural variation to develop crop varieties that produce higher yields, resist diseases, or tolerate drought. By selecting plants with desirable inherited characteristics and breeding them over many generations, scientists can develop crops that are better suited to different environments and help improve food security.
Did You Know?
Your fingerprints are unique, even if you have an identical twin. Although identical twins share almost the same DNA, tiny differences in conditions inside the womb during development create unique fingerprint patterns for each individual.
Key Terms
Acquired characteristic – A characteristic that develops during an individual's lifetime and is not inherited genetically.
Characteristic – A feature or trait of an organism.
Inherited characteristic – A characteristic passed from parents to offspring through genes.
Population – A group of individuals of the same species living in the same area.
Species – A group of organisms that can reproduce with one another and produce fertile offspring.
Variation – Differences in characteristics between individuals of the same species.
Key Takeaways
- Variation refers to the differences between individuals of the same species.
- Individuals differ because of inherited genes, environmental influences, or a combination of both.
- Inherited characteristics are passed from parents to offspring, while acquired characteristics develop during an individual's lifetime and are not inherited.
- Variation can be continuous (a range of values) or discontinuous (distinct categories).
- Variation is important because it helps populations survive environmental changes and provides the basis for evolution by natural selection.
- Scientists study variation to improve agriculture, medicine, conservation, and our understanding of life on Earth.