What Is Natural Selection?
Natural selection is the process by which organisms with heritable traits better suited to their environment tend to survive and reproduce more successfully than others, gradually shifting the traits of a population over generations.
Natural selection is differential survival and reproduction based on heritable traits: individuals with advantageous traits pass more copies of their genes to the next generation, driving evolutionary adaptation.
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Step-by-step worked examples
In a beetle population, the color allele frequency is p = 0.2 with a selection coefficient s = 0.3 favoring it. Find the frequency in the next generation.
p' = p(1+s)/(1+sp) = 0.2×1.3/(1+0.3×0.2) = 0.26/1.06 ≈ 0.245 (24.5%)
A population of 1,000 birds has 40 individuals carrying a beneficial beak-shape allele (p = 0.04). With s = 0.5, estimate next-generation frequency.
p' = p(1+s)/(1+sp) = 0.04×1.5/(1+0.5×0.04) = 0.06/1.02 ≈ 0.0588 (5.88%) — a modest one-generation increase
Peppered moths: before industrial pollution the dark allele frequency was p = 0.01. Pollution gives dark moths s = 0.4 fitness advantage. Compute the frequency after one generation.
p' = p(1+s)/(1+sp) = 0.01×1.4/(1+0.4×0.01) = 0.014/1.004 ≈ 0.0139 (1.39%) — small early gains compound over many generations
Flashcards
Quick quiz
Q1.Which is required for natural selection to occur?
Q2.What does a selection coefficient (s) close to 0 mean?
Q3.'Survival of the fittest' most accurately means…
Q4.Natural selection directly changes what, generation to generation?
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Common mistakes
Natural selection means organisms 'try' to adapt. — Correct: Selection acts on existing random variation — organisms don't choose to evolve.
Natural selection always leads to 'perfect' organisms. — Correct: Selection produces 'good enough' adaptations limited by trade-offs and history, not perfection.
An individual organism evolves during its lifetime. — Correct: Populations evolve over generations; individuals only develop or acclimate.
Fitness means being physically strong. — Correct: Fitness means relative reproductive success, which can favor small, camouflaged, or fast-breeding traits.
FAQ
What is natural selection?
Natural selection is the process by which individuals with heritable traits better suited to their environment survive and reproduce more, shifting a population's traits over generations.
What is the formula for natural selection?
For simple haploid selection, the allele frequency formula is p' = p(1+s)/(1+sp), where s is the selection coefficient.
What are examples of natural selection?
The peppered moth's coloration, antibiotic resistance in bacteria, and beak-size variation in Darwin's finches are classic examples.
How is natural selection different from genetic drift?
Selection is a non-random, fitness-based process; genetic drift is random chance, and its effects are strongest in small populations.