Step 1: Variation: A population must contain individuals with different versions of a trait, usually resulting from genetic mutations or sexual recombination.
Step 2: Selection Pressure: An environmental change or challenge occurs, such as a new predator or a change in climate, which makes certain traits more beneficial than others.
Step 3: Survival of the Fittest: Individuals with the advantageous phenotype survive the selection pressure at a higher rate than those without it.
Step 4: Reproduction and Inheritance: Survivors reproduce and pass the advantageous alleles to their offspring, ensuring the trait persists in the next generation.
Step 5: Allele Frequency Shift: Over many generations, the frequency of the advantageous allele increases while the non-advantageous allele decreases, leading to evolution.
| Feature | Adaptation | Evolution |
|---|---|---|
| Level | Individual/Trait | Population/Species |
| Mechanism | Result of selection | Cumulative process |
| Timeframe | Immediate utility | Multi-generational |
The V-S-S-R-I Framework: When answering long-form questions, always structure your response using the sequence: Variation (due to mutation), Selection pressure, Survival, Reproduction, and Inheritance of alleles.
Focus on Alleles: Marks are often lost by discussing 'traits' without mentioning 'alleles.' Always specify that it is the advantageous allele that increases in frequency within the gene pool.
Avoid Teleology: Never suggest that organisms 'evolve to' or 'change because they need to.' Evolution is a passive, reactive process based on existing variation, not a conscious or purposeful one.
Population vs. Individual: Always state that populations evolve over time, while individuals are selected. An individual cannot change its alleles during its lifetime to adapt to a pressure.
'Survival of the Strongest': This is a common error; fitness refers to reproductive success, not physical strength. A small, weak organism that produces many offspring is more 'fit' in biological terms than a strong one that produces none.
Acquired Characteristics: Students often mistakenly believe that traits acquired during an organism's life (like muscle growth) can be passed on. Only changes in the DNA of germ cells (alleles) can be inherited by the next generation.
Mutation Purpose: Mutations are random and do not occur 'in response' to a need. The environment simply filters the mutations that already exist or occur by chance.
