Prep 4 Pop Quiz
📚 Darwinian Evolution OverviewBrief Overview
This note covers Darwinian Evolution and was created from a 14‑minute audio lecture on Darwin and evolution.
It covers natural selection, adaptation, species diversity, environmental pressures, and human‑directed breeding.
Key Points
Charles Darwin’s observations on the Galápagos Islands
The four‑step cycle of natural selection
Evidence of adaptation in tortoises and pigeons
Distinction between natural and artificial selection
📚 Key Concepts & Essential Questions
Essential Question: Who was Charles Darwin?
Essential Question: How does Darwin’s theory of evolution by natural selection explain how species change over time?
Essential Question: How are adaptations evidence of natural selection?
🧑🔬 Charles Darwin
Naturalist (person who studies plants and animals by observing them).
Served as the naturalist on the HMS Spiegel, a British Navy survey ship.
During his world‑wide voyage he collected and observed many organisms, especially on the Galápagos Islands.
🐦 Bird Diversity
Scientists estimate ≈ 10,000 bird species alive today.
All birds share wings, feathers, and a beak.
Hypothesis: all birds descended from an ancestral bird‑like population that diversified into many species with different sizes, colors, songs, and diets.
🐢 Galápagos Tortoises
The Galápagos archipelago lies ~1,000 km off South America in the Pacific.
Three shell/neck forms (Figure 6):
Island (example)
Shell type
Neck length
Typical vegetation
Isabela
Dome
Short
Low grasses
Santiago
Intermediate
Medium
Both low and high vegetation
Española
Saddleback
Long
Tall cacti
Tortoises on each island evolved neck lengths matching the height of available food.
🐦 Mockingbirds & Finches
Different island environments hosted distinct varieties of mockingbirds and finches.
Some varieties were distinct enough to be classified as separate species.
🔬 Variation
A variation is a slight difference in an inherited trait among individuals of a species.
Arises naturally via random mutations or genetic recombination during sexual reproduction.
Examples:
Shell shape differences in tree snails (Figure 7).
Stripe pattern differences in zebras.
🔄 Natural Selection
Natural selection is the process by which individuals with advantageous variations survive longer, compete more effectively for limited resources, and reproduce more, causing those variations to become more common in the population.
Four‑step cycle (Figure 8):
Reproduction – A population produces many offspring.
Variation – Some offspring inherit a beneficial trait (e.g., longer neck).
Competition – Limited resources mean only the best‑adapted survive.
Selection – Survivors reproduce, passing the advantageous trait onward.
Table: Natural‑Selection Process
Step | Description | Outcome |
|---|---|---|
Reproduction | Many offspring are born. | Genetic pool expands. |
Variation | Offspring differ slightly (e.g., neck length). | New traits appear. |
Competition | Food is limited; not all survive. | Advantageous traits confer survival. |
Selection | Survivors reproduce more. | Trait frequency increases. |
🛠 Adaptations
An adaptation is an inherited trait that increases an organism’s chances of surviving and reproducing in its environment.
Types of Adaptations
Category | Definition | Example |
|---|---|---|
Structural | Physical features such as shape, color, or anatomy. | Long neck of saddleback tortoise; desert jackrabbit’s large ears. |
Behavioral | Actions or patterns of activity. | Night hunting; herd movement. |
Functional | Internal physiological processes. | Hibernation lowering body temperature; metabolic adjustments. |
Camouflage & Mimicry
Camouflage – structural adaptation allowing an organism to blend into its surroundings (e.g., seahorse matching coral color).
Mimicry – resemblance to another species that deters predators (e.g., caterpillar that looks like a snake).
🌍 Environmental Factors
Living components: other organisms (prey, predators, competitors).
Non‑living components: temperature, water availability, soil nutrients, climate.
Species must adapt to both; changes in any factor can drive evolutionary change or lead to extinction.
🦋 Coevolution Example
Figure 11 illustrates a moth–pollinator pair that have evolved so tightly that each depends on the other for survival.
⚙ Artificial Selection
Artificial selection (selective breeding) is the human‑directed breeding of organisms for desired traits.
Darwin bred domestic pigeons, creating varieties with different colors and shapes (Figure 12).
Compared to natural selection, artificial selection involves human choice rather than environmental pressures.
📖 Vocabulary
Naturalist – a person who studies plants and animals through direct observation.
Variation – a slight inherited difference among individuals of a species.
Natural selection – the differential survival and reproduction of individuals due to advantageous variations.
Adaptation – an inherited trait that improves survival and reproductive success.
Camouflage – a structural adaptation that enables an organism to blend with its environment.
Mimicry – an adaptation where one species resembles another, often for protection.
Selective breeding – the intentional breeding of organisms to emphasize specific traits (artificial selection).
📝 Practice Questions
Fill in the blank: A person who studies plants and animals by observing them is a _____.
Through _____, populations adapt to their environments.
Some species blend into their environments through _____.
The observation that Galápagos tortoises inhabited different environments helped Darwin A. develop his theory of adaptation, B. develop his theory of evolution, C. observe mimicry, D. practice artificial selection.
Explain why variations are essential for natural selection.
Compare and contrast natural selection with artificial selection.
Describe how Earth’s birds achieved their diversity through natural selection.