3: Evidence of Evolution

What is microevolution?

Small changes in a population’s gene frequencies over a short time (e.g., changes in beak size).

What is macroevolution?

Large-scale evolutionary changes that create new species or groups over long periods.

How do microevolution and macroevolution relate?

Macroevolution is the result of many microevolutionary changes accumulating over time.

What is the principle of stratigraphy?

In sedimentary rock layers, older layers are found below younger layers.

How do sedimentary rocks and fossils form?

Layers of sediment build up over time, trapping and preserving organisms as fossils in the lower layers.

Why is stratigraphy important for understanding fossils?

It helps determine the relative ages of fossils based on the layer they’re found in.

How does extinction provide evidence for evolution?

Extinction shows that species have disappeared over time, meaning life has changed.

What are transitional forms in fossils?

Fossils that show features between older and newer species, linking them in evolutionary history.

Why are transitional fossils important for evolution?

They show how species gradually changed over time, supporting descent with modification.

What hypothesis were Tiktaalik’s discoverers testing?

They tested the idea that a transitional form between fish and land vertebrates (tetrapods) existed around 375 million years ago, showing how vertebrates moved from water to land.

OR 

That a transitional species existed about 375 million years ago showing both fish and tetrapod features, bridging the gap between aquatic and land animals.

How does Tiktaalik resemble modern tetrapods?

• Has a neck (can move head independently)

• Has ribs to support lungs and body

• Has limb-like fins with bones similar to wrists and elbows

• Flat skull and eyes on top of its head

How does Tiktaalik resemble fish?

• Has scales covering its body

• Has fins rather than full limbs

• Has gills for breathing underwater

• Uses fins to swim

What is a tetrapod?

A vertebrate animal with four limbs or limb-like appendages.

What are the major groups of tetrapods?

Amphibians, reptiles, birds, and mammals.

Give an example of a tetrapod.

Frog (amphibian), lizard (reptile), eagle (bird), or human (mammal).

Why is Archaeopteryx considered a transitional form between reptiles and birds?

It has features of both groups:

• Reptile traits: teeth, long bony tail, claws on wings

• Bird traits: feathers and wings for flight

Name some vestigial structures in humans and their ancestral functions.

• Appendix – used for digesting tough plants

• Wisdom teeth – helped chew coarse diet

• Tailbone (coccyx) – was a tail for balance and communication

• Goosebumps (arrector pili muscles) – made hair stand up for warmth or intimidation

Why are vestigial structures evidence for evolution?

They are leftover traits that no longer serve their original purpose, showing that species have changed over time from ancestors who used those traits.

What are the three types of homology that show common ancestry?

• Structural homology: Similar body parts with different functions.

• Molecular homology: Similar DNA or protein sequences.

• Developmental homology: Similar embryo development patterns.

Give an example of a homologous structure and two species that have it.

The forelimb bones (humerus, radius, ulna) are homologous in humans and whales, showing they share a common ancestor.

How does evolutionary history contribute to problems like varicose veins, sleep apnea, choking, hiccuping, and hernias?

These issues happen because our bodies evolved for different environments or functions (like walking upright) and some inherited structures aren’t perfectly adapted, leading to “design compromises” or vulnerabilities.

Give an example of evolution in a multicellular species within the past 50 years.

The peppered moth in England evolved darker coloring during the Industrial Revolution to better camouflage on soot-covered trees, then lightened again as pollution decreased.

Why does the NIH (National Institutes of Health) spend much of its budget on non-human organisms?

Because many animals share common genes and biology with humans, studying them helps us understand human health and disease through evolution.