Edexcel iGCSE Biology-4.38 Darwin’s Theory of Evolution by Natural Selection- Study Notes- New Syllabus

Darwin’s Theory of Evolution by Natural Selection

🔹 Introduction

Evolution = change in inherited characteristics of a species over time.
Charles Darwin (1809–1882) proposed that evolution occurs via natural selection.
Explains how species adapt and survive in changing environments.

📌 Key Points of Natural Selection

• Variation exists within a species: Individuals differ in traits (genetic & environmental).
  Example: some beetles are green, some brown.
• Overproduction of offspring: More offspring are born than can survive → competition for resources (food, shelter, mates).
• Survival of the fittest: Individuals with favourable traits are more likely to survive & reproduce. Traits improving survival = adaptations.
• Inheritance of favourable traits: Survivors pass advantageous traits to offspring → traits become more common over generations.
• Evolution over time: Gradual accumulation of changes → new species can form.

🧬 Example:
Peppered moths during Industrial Revolution:
Light moths → visible on soot-covered trees → eaten by birds
Dark moths → camouflage → survive & reproduce
Over time → population mostly dark moths

📊 Summary Table

📝 Quick Recap 
Natural selection = key mechanism of evolution.
Requires: variation + overproduction + survival of the fittest + inheritance.
Leads to adaptation and sometimes new species.
Famous example: Peppered moths.