Evolution: The Core Theme of Biology

🌍 EVOLUTION — The Core Theme of Biology

Evolution is the central foundation on which all of biology is built.
It explains:

• How living organisms change over time
• How species adapt to their environment
• Why organisms are similar (unity)
• Why organisms differ (diversity)

Definition

Evolution is:
✔ the change in the genetic makeup of a population
✔ over generations
✔ due to variation, selection, and inheritance

🔥 Natural Selection — The Engine of Evolution

Scenario

• One organism is bright red/white on green leaves → easily seen by predators → more likely to die.
• The second organism mimics the thorn of the plant (camouflage) → predators cannot easily spot it → survives better.

Process

1. Some organisms in a population naturally have advantageous traits (like camouflage).
2. These organisms survive longer and reproduce more.
3. They pass on their adaptive traits to their offspring.
4. Over generations, the population changes genetically.

This process is called:

⭐ Natural Selection

Nature selects traits that increase survival in an environment.

🌱 Evolution Explains Unity and Diversity

Unity of Life

Organisms share similarities because:

• They descended from common ancestors
• They share DNA, cells, biochemistry, etc.

Example: All fish live in water, have gills, and similar fin structures.
There is unity (similar structures) despite diversity (different species).

Diversity of Life

Organisms differ because:

• They adapt to different environments
• They evolve along different evolutionary lines

Example:

• Dinosaurs once dominated the Earth
• They went extinct
• New forms of life evolved afterwards

Evolution explains:

• Why extinct organisms differ from modern ones
• What features they share
• How species branch out over millions of years

📌 Q&A Clarified

1. How are physical characteristics transmitted during evolution?

Through reproduction, the same way children inherit traits from parents.

Natural selection ensures:

• Beneficial traits (camouflage, long neck, strong claws)
  → passed to offspring
• Harmful traits
  → eliminated gradually

Transmission is by genes (DNA), not by “trying” or choice.

2. What is the summary or meaning of “concepts that unify biology”?

These are big ideas that appear in all areas of biology, such as:

• Organization of life
• Energy flow
• Information transfer (DNA → RNA → protein)
• Homeostasis
• Interactions
• Evolution

Evolution ties all of them together.

3. Quick summary of Levels of Organization

1. Atom
2. Molecule
3. Macromolecule (biomolecule)
4. Organelle
5. Cell
6. Tissue
7. Organ
8. Organ system
9. Organism
10. Population
11. Community
12. Ecosystem
13. Biosphere

Each level becomes more complex, and new features appear.

⭐ 4. Emergent Properties (simple explanation)

Emergent properties are new characteristics that appear as we move to higher levels of organization.

Example:

• A single muscle cell cannot move your arm
• But many muscle cells together → movement (a new property)

Or:

• Hydrogen + oxygen (alone) cannot quench thirst
• Together → water (a new property)

So:

Emergent properties = new abilities that appear when parts combine.

5. Importance of RNA

• RNA acts as the interpreter between DNA and protein.
• The cell cannot read DNA directly.
• DNA → (transcription) → RNA → (translation) → Protein

Functions:

• Some viruses use RNA as genetic material
• RNA carries instructions for protein synthesis
• RNA helps in regulation and gene expression