The short answer
Why evolution is differential reproduction — not 'survival of the strongest' — and what selection actually acts on.
Written and checked by GAMSAT tutors — not AI-generated.
Try the reasoning style
We treat forgetting as a failure — a lapse to be patched with reminders and records. Yet a mind that kept everything could not think; it would drown in the undifferentiated noise of every moment it had ever lived. To forget is not so much to lose information as to decide, mostly without our noticing, what was never worth keeping.
The author's argument relies most directly on which unstated assumption?
Pick an option to see how the tutor reasons to the answer — not just whether you were right.
Not quite — the answer is B.
Work backwards from the conclusion: a mind that ‘kept everything’ supposedly ‘could not think.’ That only follows if thinking means leaving most of experience out — so B is the premise the argument quietly rests on. A raises reliability, which the passage never weighs; C contradicts ‘mostly without our noticing’; D smuggles in a claim about intellect the passage never makes. The question rewards finding the hidden premise, not recalling a fact.
Evolution isn't "survival of the strongest" — it's differential reproduction. Individuals that happen to be better suited to their environment leave more offspring, so their traits become more common over generations. Get the logic and you can reason through any selection scenario.
The four ingredients
Natural selection needs: (1) variation in a trait, (2) that variation is heritable, (3) more offspring are produced than can survive (competition), and (4) individuals with advantageous traits have greater reproductive success. Over time, the helpful alleles rise in frequency.
Two traps to avoid
Individuals don't evolve — populations do. A giraffe doesn't stretch its neck and pass that on; rather, longer-necked giraffes left more offspring. And organisms don't "try" to adapt: variation is random (mutation), but selection is not — the environment does the filtering.
Worked example
A population of bacteria is exposed to an antibiotic. A few cells carry a random mutation for resistance. Explain, in selection terms, why the population becomes resistant.
Check yourself
Natural selection acts directly on an organism's:
Key takeaways
- Evolution = change in allele frequencies in a population over time.
- Requires variation, heritability, competition, and differential reproduction.
- Mutation (variation) is random; selection is not.
- Populations evolve, not individuals; selection acts on the phenotype.
- Antibiotic/pesticide resistance is natural selection in fast-forward.
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