Variation Within Species
3. Environmental Variation
Learning outcomes
- I can define environmental variation.
- I can identify environmental factors that influence traits.
- I can distinguish between genetic and environmental causes of variation.
- I can explain how lifestyle and surroundings affect organisms.
- I can analyse examples of environmental variation.
Introduction
Not all differences between individuals are caused by genes. Two people may have similar genetic potential for height, but one may grow taller because they had a healthier diet during childhood. A plant grown in rich soil may be much larger than the same type of plant grown in poor soil, even though their genes are very similar.
These differences are examples of environmental variation. Environmental factors influence how organisms grow, develop, and survive throughout their lives. Many characteristics are shaped by both genetics and the environment, making environmental variation an important part of biology.
What Is Environmental Variation?
Environmental variation refers to differences in characteristics that are caused by environmental factors rather than inherited genes.
Environmental variation occurs because organisms experience different conditions during their lives.
Examples include:
- Body mass.
- Muscle strength.
- Suntan.
- Plant height.
- Language spoken.
- Scars.
These differences are not caused directly by inherited DNA.
Figure 1. Environmental conditions can cause individuals with similar genes to develop differently.
Environmental Factors
Many environmental factors influence the characteristics of organisms.
Common factors include:
- Nutrition.
- Temperature.
- Light.
- Water availability.
- Exercise.
- Disease.
- Climate.
- Pollution.
Different environments can produce different outcomes, even within the same species.
Nutrition
Food provides the energy and nutrients needed for growth and development.
Examples:
- Children with balanced diets usually grow more effectively.
- Plants supplied with enough minerals often grow larger and healthier.
Poor nutrition can reduce growth even when genes would allow greater growth.
Climate and Temperature
Climate affects many living organisms.
Examples include:
- Animals in colder regions often develop thicker fur.
- Plants grow differently in tropical and desert environments.
- Temperature influences the growth rate of many organisms.
Environmental conditions can affect how genes are expressed.
Figure 2. Environmental conditions such as climate can influence the appearance and survival of organisms.
Exercise and Lifestyle
Lifestyle choices influence many characteristics.
Examples include:
- Exercise increases muscle size and strength.
- Regular training improves fitness.
- Poor sleep can affect growth and health.
- Smoking may damage the lungs.
- Excessive sun exposure causes tanning.
These are examples of environmental variation because they develop during life.
Disease
Illness can influence growth and development.
Examples include:
- Disease reducing plant growth.
- Childhood illnesses affecting physical development.
- Parasites reducing body condition in animals.
Disease is an environmental factor because it is not inherited directly as a characteristic.
Genetic vs Environmental Variation
Many characteristics are influenced mainly by either genes or the environment.
| Mainly Genetic | Mainly Environmental |
|---|---|
| Blood group | Suntan |
| Natural eye colour | Scars |
| Natural hair colour | Muscle development |
| Earlobe attachment. | Language spoken |
Some characteristics depend on both.
Characteristics Influenced by Both
Many traits result from a combination of genes and environment.
Examples include:
Height
Affected by:
- Genes.
- Nutrition.
- Health.
Body Mass
Affected by:
- Genes.
- Diet.
- Exercise.
- Lifestyle.
Intelligence and Learning
Influenced by:
- Genetics.
- Education.
- Environment.
- Experience.
Most complex characteristics involve interactions between genes and environmental factors.
Figure 3. Many characteristics result from both inherited genes and environmental influences.
Analysing Environmental Variation
When studying variation, scientists ask:
- Is the characteristic inherited?
- Is it caused by the environment?
- Is it influenced by both?
For example:
A person develops large muscles after years of weight training.
The increased muscle size is mainly due to exercise, making it an example of environmental variation.
Why Environmental Variation Is Important
Environmental variation allows organisms to respond to changing conditions.
It helps explain why:
- The same species looks different in different environments.
- Individuals grow at different rates.
- Lifestyle influences health.
- Organisms adapt to their surroundings during their lifetime.
Unlike genetic variation, environmental variation is not inherited by offspring.
Examples of Environmental Variation
Examples include:
Humans
- Suntans.
- Scars.
- Muscle growth.
- Fitness level.
- Language learned.
Plants
- Height.
- Number of leaves.
- Growth rate.
- Flower size.
Animals
- Body condition.
- Fur thickness (seasonal changes).
- Weight.
- Behaviour learned through experience.
Environmental variation occurs throughout the living world.
Figure 4. Environmental variation can affect the appearance, growth, and behaviour of many organisms.
Environmental Variation and Survival
Although environmental variation is not inherited, it can improve an individual's chances of survival.
Examples:
- Regular exercise improves fitness.
- Good nutrition promotes healthy growth.
- Adequate water helps plants survive drought.
- Learning helps animals avoid predators.
These changes benefit the individual but are generally not passed genetically to offspring.
Worked Example
Question
Classify each characteristic as:
- Genetic
- Environmental
- Both genetic and environmental
Characteristics:
- Blood group
- Height
- Suntan
- Muscle development
- Eye colour
Solution
| Characteristic | Classification |
|---|---|
| Blood group | Genetic |
| Height | Both |
| Suntan | Environmental |
| Muscle development. | Environmental |
| Eye colour | Genetic |
Real-World Connection
Farmers carefully manage environmental conditions to help crops grow successfully. They control factors such as water, soil nutrients, sunlight, and temperature to improve plant growth and increase crop yields. Even plants with excellent genetic potential cannot reach their full size or produce healthy fruits if environmental conditions are poor.
Did You Know?
Identical twins have almost exactly the same DNA, yet they often become more different in appearance, health, and even personality as they grow older. Different diets, occupations, hobbies, illnesses, and life experiences create environmental variation, making each twin increasingly unique over time.
Key Terms
Environmental factor – A condition in an organism's surroundings that influences its growth, development, or characteristics.
Environmental variation – Differences in characteristics caused by environmental factors rather than inherited genes.
Genetic variation – Differences in characteristics caused by inherited genes.
Lifestyle – The way an individual lives, including diet, exercise, sleep, and other habits that affect health.
Trait (Characteristic) – A feature or quality of an organism.
Key Takeaways
- Environmental variation refers to differences in characteristics caused by environmental factors rather than inherited genes.
- Common environmental factors include nutrition, climate, exercise, disease, light, water, and pollution.
- Some characteristics are mainly genetic, some are mainly environmental, and many are influenced by both.
- Lifestyle and surroundings can strongly affect growth, health, and development.
- Environmental variation helps explain differences between individuals living in different conditions.
- Unlike genetic variation, environmental variation is generally not inherited by offspring.