Darwinian Evolution & Natural Selection

How can you define evolution in three words (BIO 103 definition)?

Descent with modification

What is Natural Selection?

The process by which individuals with heritable traits that provide an advantage survive and reproduce more successfully, passing those traits on to future generations.

What are the four main components (tenets) of Natural Selection?

. Variation, 2. Heritability, 3. Differential survival and reproduction, 4. Selection on advantageous traits.

What is adaptation?

A trait common in a population that improves function or survival in a specific environment (e.g., bat echolocation, lizard tails breaking off).

What did Darwin postulate?

• Traits are heritable

• More offspring are produced than can survive

• Variation exists among individuals

• Those with advantageous traits survive and reproduce more successfully.

Does natural selection act on individuals or populations?

It acts on individuals, but populations evolve over time.

What is the difference between microevolution and macroevolution?

Microevolution is small-scale evolution within a population (e.g., antibiotic resistance), while macroevolution is large-scale, leading to new species (e.g., origin of mammals).

Who were the four major pre-Darwinian thinkers and what did they contribute?

• Erasmus Darwin: Proposed that life evolved from a single common ancestor.

• Charles Lyell: Introduced Uniformitarianism—slow geological changes show Earth is ancient.

• Thomas Malthus: Claimed species overproduce; competition for resources limits growth.

• Jean-Baptiste Lamarck: Proposed inheritance of acquired traits (use/disuse theory).

How would Darwin and Lamarck explain the long neck of giraffes differently?

Lamarck: Giraffes stretched their necks and passed that trait on.
Darwin: Giraffes with longer necks survived better and reproduced more.

Who was Alfred Russel Wallace and what was his contribution?

Wallace independently developed the idea of natural selection and inspired Darwin to publish On the Origin of Species.

What were Darwin’s three important observations?

• Individuals in a population vary in inherited traits.

• All species produce more offspring than can survive.

• Species are derived from common ancestors (descent with modification).

What is the significance of the Recurrent Laryngeal Nerve example?

It shows how evolution reuses existing structures inefficiently, evidence of descent with modification.

What are the six major lines of evidence for evolution?

• Direct Observation

• Homology (Homologous & Vestigial Structures)

• Fossil Record

• Biogeography

• Molecular Biology

• Comparative Embryology

What are examples of direct observation of evolution?

Peppered moth color changes, antibiotic-resistant bacteria, pesticide-resistant insects, finch beak variation.

What is a homologous structure and why is it important?

Structures with similar anatomy from a common ancestor but different functions (e.g., human arm, whale flipper). It proves common ancestry.

What is a vestigial structure?

A reduced structure that no longer serves its original function (e.g., human appendix, whale pelvis, snake pelvis).

What does comparative embryology show?

Early embryos of vertebrates share traits like tails and pharyngeal pouches, indicating common ancestry.

What is convergent evolution?

When unrelated species evolve similar traits due to similar environments (e.g., sharks and dolphins, arctic fox and ptarmigan).

What does the fossil record show?

Transitional fossils, extinction events, and gradual changes over time (e.g., whale evolution from land mammals, Tiktaalik).

What is Tiktaalik and why is it important?

A transitional fossil linking fish and amphibians (~375 mya) with both gills and early limb bones.

What is Archaeopteryx and what traits did it have?

A transitional fossil between dinosaurs and birds; reptile traits (teeth, long tail) and bird traits (feathers, wishbone).

What does whale evolution show?

Gradual loss of hind limbs and development of tail flukes; shows transition from land mammals to aquatic life.

What is biogeography?

The study of species distribution based on geography and history (e.g., marsupials in Australia, lemurs in Madagascar).

How does molecular biology support evolution?

Similar DNA sequences and protein structures show genetic relationships among species.

Name common misconceptions about evolution.

• Evolution is “just a theory.”

• Individuals evolve.

• Evolution explains the origin of life.

• Evolution has a purpose or goal.

What was Darwin’s ship and what did he study there?

The HMS Beagle; he studied finches and tortoises on the Galápagos Islands.

What is the biological meaning of “fitness”?

An organism’s ability to survive and reproduce in its environment.

Who was Jean-Baptiste Lamarck?

Lamarck proposed that organisms evolve by inheriting traits acquired during their lifetime, introducing the idea that species change over time.

Who was Charles Lyell?

Lyell’s theory of Uniformitarianism showed that Earth changes slowly over long periods, helping Darwin realize evolution also occurs gradually.

Who was Thomas Malthus?

Malthus argued that population growth outpaces resources, inspiring Darwin’s idea of competition driving natural selection.

Who was Erasmus Darwin?

Erasmus Darwin, Charles’s grandfather, suggested that all life evolved from a common ancestor, influencing Darwin’s view of shared origins.