VARIATION refers to the differences in characteristics between individuals of the same species.
Variation is absolutely essential for life on Earth:
It is the raw material on which NATURAL SELECTION acts.
Without variation, all individuals would be identical and no evolutionary change would be possible.
Variation allows populations to adapt to changing environments.
Variation can be:
CONTINUOUS — characteristics that show a range of values with no distinct categories (e.g. height, weight, skin colour).
DISCONTINUOUS — characteristics that fall into distinct categories with no in-between values (e.g. blood group A, B, AB or O; tongue rolling ability; ability to taste PTC).
Causes of Variation
Variation arises from three main sources:
1. GENETIC VARIATION:
Differences in DNA sequences between individuals.
Arises through: MUTATIONS (random changes in DNA sequence), MEIOSIS (shuffling of chromosomes and crossing over), SEXUAL REPRODUCTION (combining DNA from two parents).
Genetic variation is INHERITED — passed from parents to offspring.
2. ENVIRONMENTAL VARIATION:
Differences caused by conditions an organism experiences during its lifetime.
Examples: height (affected by nutrition during childhood), skin colour (affected by sun exposure), language spoken (learned from environment), scars and injuries.
Environmental variation is NOT inherited — you cannot pass on a learned language or a scar to your offspring.
3. COMBINATION OF BOTH:
Many characteristics are influenced by BOTH genes AND environment.
Examples: height (genes set the potential maximum; nutrition determines whether that potential is reached), body weight (genes influence metabolism; diet and exercise are environmental), skin colour (genes determine base colour; UV exposure adds a tan).
Mutations
A MUTATION is a change in the sequence of DNA bases in a gene or chromosome.
Mutations can be:
Spontaneous — occurring randomly during DNA replication (copying errors).
Induced — caused by MUTAGENS: chemicals (e.g. carcinogens in tobacco smoke), radiation (UV, gamma rays, X-rays), certain viruses.
Effects of mutations:
Most mutations are NEUTRAL — they occur in non-coding DNA or don't change the protein significantly.
Some mutations are HARMFUL — they alter a protein so it cannot function properly (e.g. mutations causing cystic fibrosis, sickle cell disease).
Very occasionally, a mutation is BENEFICIAL — it improves the function of a protein or produces a new useful function (e.g. mutations that gave early humans more efficient enzymes or better immune responses).
Beneficial mutations are the ultimate source of all new variation in a species — they are the raw material on which natural selection acts.
⚠️ Common Mistake
Environmental variation is NOT inherited — you cannot pass your experiences, injuries or learned skills to your children through DNA. Genetic variation IS inherited. Most mutations are neutral — not harmful. Students often assume all mutations are dangerous, but the vast majority have no detectable effect.
📌 Key Note
Variation: continuous (range of values) or discontinuous (distinct categories). Causes: genetic (mutation, meiosis, sexual reproduction), environmental (nutrition, sun, learned). Many traits = combination of both. Mutations: neutral, harmful or rarely beneficial.
🎯 Matching Activity — Genetic, Environmental or Both?
Match each example to the cause of variation. — drag the symbols on the right to match the component names on the left.
Genetic
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Environmental
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Both
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Environmental
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Genetic
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Both
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Language spoken — entirely learned from the surrounding environment
Body weight — metabolic rate is genetic; diet and exercise are environmental
Blood group — determined entirely by inherited alleles
Height — genes set the maximum potential; nutrition determines if it is reached
Cystic fibrosis — caused by inheriting two copies of the recessive allele
A scar from a childhood accident — not passed to offspring
🎯 Test Yourself
Question 1 of 3
1. A child is taller than expected given their parents' heights. What is the most likely cause?
2. Which of the following is an example of DISCONTINUOUS variation?
3. What is a mutation?
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