IB MYP 4-5 Biology-Natural selection- Study Notes - New Syllabus
IB MYP 4-5 Biology-Natural selection- Study Notes – New syllabus
IB MYP 4-5 Biology-Natural selection- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Darwin’s theory of evolution
- Adaptations and survival advantage
- Evidence for evolution (fossils, homologous structures)
Darwin’s Theory of Evolution
By Charles Darwin – “Father of Evolution”
What is Evolution?
Evolution is the process by which living organisms slowly change over long periods of time. These changes help them adapt to their environment, survive, and reproduce.
Who Was Charles Darwin?
Darwin was a British naturalist. In 1859, he published On the Origin of Species, where he introduced the idea of species changing over time through natural selection.
What is Darwin’s Theory of Evolution?
Darwin proposed that all living things evolved from earlier forms via a process called natural selection.
Key Ideas in Darwin’s Theory:
1. Variation Exists
- Every species has individual differences.
- Example: Some giraffes have longer necks.
- Caused by genetics and mutations.
2. Struggle for Survival
- More organisms are born than can survive.
- They compete for food, space, and mates.
3. Survival of the Fittest
- Those with traits better suited to the environment survive and reproduce.
- This is natural selection.
4. Favorable Traits Are Passed On
- Helpful traits are inherited and become more common.
- Example: Thicker fur in cold climates helps survival.
5. New Species May Evolve
Over many generations, small changes can lead to new species.
🦎 Real-Life Example: Darwin’s Finches
Darwin studied finches in the Galapagos Islands. Each had different beak shapes suited for different foods – evidence of natural selection.
Summary Table – Darwin’s Theory
| Principle | Description |
|---|---|
| Variation | Differences exist among individuals |
| Overproduction | More offspring are born than can survive |
| Natural Selection | Best adapted survive and reproduce |
| Speciation | New species may form over time |
| Competition | Struggle for food, space, mates |
| Adaptation | Helpful traits become more common |
Is Evolution Still Happening?
Yes! Evolution is a slow and ongoing process. Examples include:
- Bacteria becoming antibiotic-resistant
- Insects becoming immune to pesticides
- Animals adapting to climate change
“Organisms change over time because those best adapted to the environment survive and pass on their traits.”
Adaptations and Survival Advantage
What Are Adaptations?
Adaptations are special features or behaviors that help an organism survive, reproduce, and thrive in its environment.
These can be:
- Structural (body parts or physical traits)
- Behavioral (how they act)
- Physiological (how their body works internally)
Why Are Adaptations Important?
- They give organisms a survival advantage
- Help them find food, avoid predators, cope with climate, or reproduce
- Better-adapted organisms outlive others
Types of Adaptations
1. Structural Adaptations (Body Features)
Physical changes that help organisms survive.
| Example | Survival Advantage |
|---|---|
| Long neck in giraffes | Reach high tree leaves for food |
| Webbed feet in ducks | Swim better in water |
| Sharp teeth in lions | Tear meat easily |
| Camouflage in chameleons | Blend with surroundings to avoid predators |
2. Behavioral Adaptations (Actions or Habits)
Behaviors that help in survival.
| Example | Survival Advantage |
|---|---|
| Birds migrating in winter | Avoid cold and find food |
| Nocturnal animals | Stay safe from daytime predators |
| Bears hibernating | Survive winter with low energy use |
3. Physiological Adaptations (Internal Functions)
Internal processes that support survival.
| Example | Survival Advantage |
|---|---|
| Snake venom | Helps in catching prey or self-defense |
| Desert plants storing water | Survive long dry periods |
| High red blood cells in mountain animals | Breathe better in thin air |
How Adaptations Give Survival Advantage
- Increase chances of survival
- Let organisms reproduce successfully
- Pass on traits to next generation → evolution
This is the idea behind Darwin’s Natural Selection
Examples from Nature
| Organism | Adaptation | Advantage |
|---|---|---|
| Polar bear | Thick white fur | Warmth + camouflage |
| Cactus | Spines instead of leaves | Reduces water loss |
| Arctic fox | Small ears | Less heat loss |
| Fish | Gills | Breathe underwater |
Adaptation ≠ Instant Change
Adaptations happen over generations through genetic variation and natural selection.
What If an Organism Can’t Adapt?
It may struggle to survive and could go extinct.
Example: Dinosaurs → couldn’t adapt → extinction
Key Points to Remember
- Adaptations help organisms survive in their environment
- They can be structural, behavioral, or physiological
- Provide a survival advantage and increase reproduction chances
- Drive evolution through natural selection
- Lack of adaptation may lead to extinction
Evidence for Evolution
What is Evolution?
Evolution is the gradual change in living organisms over millions of years. Scientists believe all life today evolved from common ancestors. But how do we prove that? Let’s explore the evidence that supports the theory of evolution.
1. Fossils – Traces of the Past
What are Fossils?
Fossils are the preserved remains, impressions, or traces of organisms that lived long ago, found in rocks, ice, amber, or tar. They can include:
- Bones
- Shells
- Footprints
- Leaf imprints
How Do Fossils Support Evolution?
- Fossils show how organisms have changed over time
- They create a fossil record – a timeline of life on Earth
- Older rocks = simpler organisms, Newer rocks = complex organisms
- Transitional forms show evolution in action
Example: Evolution of Horses
- Early horses were small with toes
- Over millions of years, evolved into larger horses with hooves
- Fossils show gradual changes in leg, tooth, and body size
Transitional Fossils
Definition: Fossils that link two groups of organisms
Example: Archaeopteryx – had feathers like birds but teeth and claws like reptiles → shows link between birds and reptiles
2. Homologous Structures – Same Inside, Different Outside
What Are Homologous Structures?
Body parts in different species with similar internal structure but different function.
Suggests: These species had a common ancestor.
Examples of Homologous Structures
| Organism | Body Part (Structure) | Function |
|---|---|---|
| Human | Arm bone | Lifting, writing |
| Whale | Flipper | Swimming |
| Bird | Wing | Flying |
| Cat | Front leg | Walking/climbing |
Why Is This Evidence?
- The same basic structure is reused in different ways
- Shows animals evolved from a common ancestor
- Different functions reflect adaptation to environments
Other Evidence for Evolution:
DNA and Genetics
- All living things share similar genetic code
- Humans and chimpanzees share 98–99% of DNA
- Shows close evolutionary relationship
Embryo Development
- Early embryos of fish, birds, and humans look similar
- Suggests a shared starting point in development
Differences appear later as the embryo matures
Summary Table – Key Evidence
| Evidence Type | What It Shows |
|---|---|
| Fossils | Organisms changed over time. links between old and new species |
| Homologous structures | Common ancestry, same bone structure in different species |
| DNA similarities | Genetic links between species |
| Embryo development | Shared early development stages |
Final Recap
- Fossils show how organisms have changed over time
- Homologous structures show links between species
- DNA and embryo studies support common ancestry
- All support that evolution is real and ongoing