Charles darwin
1. Variation (Darwin’s Core Discovery)
Darwin observed that no two individuals of the same species are exactly alike.
Variations can be:
Size
Shape
Color
Beak length
Strength
Behavior
Some variations help survival, others don’t.
👉 Example: Some birds had stronger or longer beaks, allowing them to eat certain foods better.
2. Variation in Birds (Galápagos Finches)
Darwin’s most famous animal study.
Finches lived on different islands.
All finches were closely related but had different beaks.
Beak Adaptations:
Thick, strong beaks → crack seeds
Long, pointed beaks → eat insects
Sharp beaks → feed on cactus
✔ Same ancestor✔ Different environments✔ Different adaptations
➡ This proved adaptive variation
3. Variation in Animals
Darwin noticed variations across many animals:
Tortoises (Galápagos)
Different shell shapes on different islands
Long necks where food was high
Short necks where food was low
Mammals (Fossils & Living Species)
Fossils resembled modern animals in the same region
Showed descent with modification
4. Struggle for Existence
Darwin realized:
More offspring are produced than can survive.
Food and space are limited.
This causes competition.
➡ Not all individuals survive.
5. Natural Selection
Because of variation + struggle:
Individuals with useful traits survive
They reproduce more
Their traits pass to offspring
This leads to:
Gradual change
Adaptation
New species over time
📌 “Survival of the fittest” (phrase later used, not by Darwin originally)
6. Inheritance of Variations
Helpful variations are inherited
Harmful variations disappear
Over many generations, populations change
➡ Evolution is slow and continuous
7. Speciation (Formation of New Species)
When populations:
Become isolated (islands, mountains)
Experience different environments
They:
Accumulate different variations
Can no longer interbreed
➡ New species form
8. Other Key Animal Observations
Homologous structures: Same structure, different function(e.g., human arm, bat wing, whale flipper)
Embryology: Early embryos of animals look similar
Vestigial organs: Useless structures (appendix, tailbone)
All supported evolution.
9. Sexual Selection
Some traits help in attracting mates, not survival.
Examples:
Peacock’s tail
Deer antlers
Bird songs
➡ These traits spread because they increase reproduction.
10. Descent with Modification
Species are not fixed
They change over generations
All life shares common ancestry