📌Definition Table

Term	Definition
Fossil Record	Preserved remains or traces of organisms that provide chronological evidence of life’s history.
Transitional Fossil	Fossil showing intermediate traits between ancestral and descendant groups.
Comparative Anatomy	Study of similarities and differences in organism structures to infer evolutionary relationships.
Homologous Structures	Anatomical features derived from a common ancestor but adapted for different functions.
Analogous Structures	Features with similar functions but different evolutionary origins.
Molecular Evidence	DNA, RNA, and protein sequence comparisons revealing genetic relationships.
Biogeography	Study of species distribution patterns across geographical locations.

📌Introduction

Multiple lines of evidence, from fossils to molecular comparisons, demonstrate that all life shares a common origin and has diversified over time. These independent but converging data sets provide a robust framework for understanding how life evolved on Earth.

📌 Fossil Record

• Older strata contain simpler organisms, younger strata contain more complex forms.
• Transitional fossils (e.g., Archaeopteryx) link major groups.
• Provides chronological evidence of change and extinction events.
• Reveals adaptive radiations after mass extinctions.

🧠 Examiner Tip: Always note that the fossil record is incomplete due to preservation bias and erosion.

📌 Comparative Anatomy

• Homologous structures (e.g., vertebrate forelimbs) show divergent evolution.
• Analogous structures (e.g., bird vs. insect wings) show convergent evolution.
• Vestigial structures (e.g., whale pelvis, human appendix) indicate evolutionary remnants.
• Supports inference of common ancestry or similar selective pressures.

🧬 IA Tips & Guidance: Measure and compare homologous bone lengths across species to model evolutionary relationships.

📌 Molecular Evidence

• DNA sequence similarities indicate relatedness (more similarities → closer relation).
• Protein sequences (e.g., cytochrome c) act as molecular clocks.
• Highly conserved genes across taxa (e.g., HOX genes) show shared ancestry.

🌐 EE Focus: Compare molecular clock results with fossil record dates to test evolutionary timelines.

📌 Embryological Evidence

• Early embryonic stages of vertebrates share features like gill slits and tails.
• Similar developmental pathways suggest common ancestry.
• Differences arise in later development due to divergent evolution.

❤️ CAS Link: Create an educational poster showing vertebrate embryonic similarities and differences.

📌Biogeography

• Species distribution patterns reflect evolutionary history.
• Island species (e.g., Darwin’s finches) show adaptive radiation from common ancestors.
• Continental drift explains related fossils on now-distant continents.

📌 Observed Evolution in Real Time

• Examples: antibiotic resistance in bacteria, pesticide resistance in insects.
• Documented allele frequency changes over generations.
• Shows that evolution is ongoing and observable.

🔍 TOK Perspective: Evidence is interpreted through current scientific models; interpretations may change with new data.

📝 Paper 2: Data Response Tips: Be ready to interpret fossil diagrams, anatomical comparisons, DNA sequence tables, or geographic distribution maps.