🎓 Prepared by students from Boğaziçi University

What is Evolution?

Evolution is the gradual change in populations over time through mechanisms like natural selection, genetic drift, and gene flow. All life shares common ancestry, shaped by millions of years of adaptation to environments.

Short answer

Evolution is the change in allele frequencies in populations over generations, driven by natural selection (survival of the fittest), mutation, genetic drift, and gene flow.

Mechanisms of Evolution

1
Variation
Genetic differences exist within populations (mutations, recombination).
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2
Inheritance
Traits are passed to offspring through genes.
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3
Selection
Organisms with favorable traits survive and reproduce more.
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4
Allele Frequency Change
Over generations, beneficial alleles increase; harmful ones decrease.

Step-by-step worked examples

Peppered Moths: explain industrial melanism.

Pre-industrial: light moths camouflaged on lichen-covered trees → light moths dominated.
Industrial England: trees covered in soot, light moths became visible.
Predators ate more light moths → dark moths survived more.
Result: dark moths became 90%+ of the population in polluted areas (selection in action).

Darwin's Finches: how did 13 species evolve from one ancestor?

Ancestor: one finch species colonized the Galápagos.
Geographic isolation: different islands → different populations.
Different food sources per island (seeds, insects, cactus) → different selection pressures.
Beak size diverged → reproductive isolation → separate species evolved.

Antibiotic resistance in bacteria: why does it spread so quickly?

Before antibiotic: bacteria population has genetic variation (some resistant genes).
Antibiotic exposure: kills non-resistant bacteria.
Resistant survivors reproduce → population becomes resistant.
Result: within weeks to months, the population is dominated by resistant strains (rapid evolution).

Flashcards

Quick quiz

Q1.Natural selection requires which of these?

Correct answer: D. All three conditions must be met for natural selection to act.

Q2.Which mechanism is random?

Correct answer: B. Drift is random sampling; selection is non-random.

Q3.What does 'survival of the fittest' mean?

Correct answer: B. Fitness = ability to survive and reproduce in the environment.

Q4.Example of rapid evolution?

Correct answer: D. All three show evolution in observable timescales.

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Common mistakes

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Evolution is directed toward a goal. — Correct: Evolution is non-directional; natural selection is reactive to the current environment.

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Organisms evolve during their lifetime. — Correct: Individuals don't evolve; populations change over generations.

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Evolution = survival of the strongest. — Correct: Evolution = survival of the best adapted to the environment.

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Genetic drift favors beneficial alleles. — Correct: Drift is random; it can fix harmful alleles or lose beneficial ones.

FAQ

How is evolution different from natural selection?

Natural selection is one mechanism; evolution is the overall change in populations driven by selection, drift, mutation, and gene flow.

Why do we have evidence evolution happened?

Fossil record, DNA homology, observed speciation, and modern examples like antibiotic resistance.

Can evolution be stopped?

No — as long as variation exists and selection pressures apply, populations evolve.

Is evolution a fact or a theory?

It's both: observations show it happens (fact), and evolutionary theory explains how.