Guided Practice
Learning Objectives
In this guided practice lesson, you will:
- Apply natural selection concepts to scenarios
- Analyze evidence for evolution
- Practice interpreting phylogenetic relationships
- Evaluate evolutionary claims with evidence
Practice Quiz
Apply your evolution knowledge to these questions. Click to reveal each answer.
Question 1: In a population of beetles, some are green and some are brown. Birds eat more green beetles. Over generations, what happens to the beetle population?
Answer: The proportion of brown beetles increases. Brown beetles have higher survival and reproduction, so brown coloration becomes more common (directional selection).
Explanation: This is natural selection in action. The environment (predation) selects for traits (brown color) that increase survival.
Question 2: What is the difference between homologous structures and analogous structures?
Answer: Homologous: similar structure due to common ancestry (human arm, whale flipper, bat wing). Analogous: similar function but different evolutionary origin (bird wing, insect wing).
Explanation: Homology indicates evolutionary relationship; analogy indicates convergent evolution (different lineages evolving similar solutions).
Question 3: Explain how antibiotic resistance in bacteria demonstrates evolution.
Answer: Some bacteria have mutations providing antibiotic resistance. When antibiotics kill susceptible bacteria, resistant ones survive and reproduce, passing resistance to offspring. The population evolves.
Explanation: This is observable evolution: variation, selection pressure (antibiotic), differential survival, inheritance of traits.
Question 4: Why are vestigial structures evidence for evolution?
Answer: Vestigial structures (like human tailbones or whale hip bones) are remnants of functional ancestral traits. They indicate common ancestry and evolutionary history.
Explanation: These structures make no sense without evolutionary history. They're like footprints of past adaptations.
Question 5: What does fitness mean in evolutionary terms?
Answer: Fitness is an organism's ability to survive and reproduce in its environment - specifically, how many viable offspring it produces compared to others.
Explanation: Evolutionary fitness is not about strength or speed. A weak organism that produces many surviving offspring has higher fitness than a strong one with few.
Question 6: How do Darwin's finches demonstrate adaptive radiation?
Answer: From one ancestral species, finches diversified into many species with different beak shapes adapted to different food sources (seeds, insects, cacti). Each species filled a different niche.
Explanation: Adaptive radiation occurs when one lineage rapidly diversifies to fill many ecological niches, often after colonizing new habitat or after extinction events.
Question 7: What is genetic drift and how does it differ from natural selection?
Answer: Genetic drift is random change in allele frequencies, especially in small populations. Natural selection is non-random, driven by environmental pressures. Drift can cause loss of beneficial alleles by chance.
Explanation: Drift is like chance; selection is like a filter. Both change populations, but drift is random while selection is directional.
Question 8: If two species share 95% of their DNA, what does this suggest about their evolutionary relationship?
Answer: They likely share a relatively recent common ancestor. Higher DNA similarity indicates closer evolutionary relationship and more recent divergence.
Explanation: DNA accumulates mutations over time. Close relatives have had less time to diverge genetically. Humans and chimps share about 98% of DNA.
Question 9: How does geographic isolation lead to speciation?
Answer: When populations are separated by barriers (mountains, water, etc.), gene flow stops. Each population experiences different mutations and selective pressures, eventually becoming different species.
Explanation: This is allopatric speciation. Without gene flow, populations diverge. Given enough time, they become reproductively isolated.
Question 10: Why do embryos of different vertebrate species look similar early in development?
Answer: They share common ancestry. Early developmental genes are highly conserved (similar across species). This embryological evidence supports common descent of vertebrates.
Explanation: Similarities in early development (pharyngeal pouches, tails) reflect shared evolutionary history, even if adult forms differ dramatically.
Next Steps
- Practice identifying types of evolutionary evidence
- Review natural selection mechanisms
- Move on to lab analysis when ready