AP Biology 7.6 Evidence of Evolution Study Notes - New Syllabus Effective 2025
AP Biology 7.6 Evidence of Evolution Study Notes- New syllabus
AP Biology 7.6 Evidence of Evolution Study Notes- AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Describe the types of data that provide evidence for evolution.
Key Concepts:
- Evidence of Evolution
7.6.A – Evidence for Evolution
💡 What’s the Big Idea?
Evolution isn’t just a theory – it’s backed by real data from multiple scientific fields. These data types give us clues about how life has changed over time and how organisms are related.
🔍 5 Main Types of Evidence That Support Evolution
1. 🧪 Molecular Data (DNA, RNA, Proteins)
- Organisms that are more closely related have more similar genetic sequences.
- Example: Humans and chimpanzees share ~98% of their DNA!
- Scientists compare genes and proteins (like hemoglobin or cytochrome c) to build evolutionary trees.
2. 🦴 Fossil Evidence
- Fossils show how organisms looked in the past and how they’ve changed over time.
- Transitional fossils show the “in-between” forms (e.g., Tiktaalik = between fish and amphibians).
- The fossil record is like a timeline of life.
3. 🧍 Morphological Evidence (Anatomy & Structures)
- Homologous structures: Same structure, different use → means common ancestry.
- Ex: Whale flipper, bat wing, and human arm all have the same bone pattern.
- Vestigial structures: Leftover traits with no current use (ex: human tailbone, wisdom teeth).
4. 🌍 Biogeography (Geographic Distribution)
- Species found in different places but with shared traits suggest common ancestors and isolation-driven evolution.
- Example: Darwin’s finches on different Galapagos Islands evolved unique beaks for different foods.
5. 🦴Embryological Evidence
- Embryos of different species (humans, chickens, fish) look very similar in early stages.
- This suggests shared developmental genes and common ancestry.
🧠 Quick Recap:
| Type of Data | What It Shows |
|---|---|
| DNA & Proteins | Genetic similarity → shared ancestry |
| Fossils | Changes over time, transitional forms |
| Anatomy | Homology = same origin, Vestigial = leftover parts |
| Biogeography | Evolution based on location and isolation |
| Embryos | Similar early development = shared genes |
7.6.A.1 – Evidence for Evolution from Many Scientific Disciplines
✅ Main Idea:
Evolution isn’t just a theory from biology class it’s supported by tons of real-world scientific evidence across many fields. All these different types of data point toward the same conclusion: species change over time, and they share common ancestors.
📊 Types of Scientific Evidence That Support Evolution:
🌍 1. Geographical Data
- Organisms that live in similar environments across the globe often develop similar adaptations, even if they’re not closely related.
- Example: Marsupials in Australia vs. placental mammals elsewhere.
- Biogeography (study of species distribution) supports common ancestry and divergence based on geographic isolation.
⛰️ 2. Geological Data
- Fossil records show gradual changes in species over time.
- Rock layers help us date fossils and understand how organisms evolved in response to environmental changes.
- Transitional fossils (like Tiktaalik, halfway between fish and amphibians) provide “missing links.”
⚛️ 3. Physical (Morphological) Data
- Homologous structures = same structure, different function (e.g., human arm, whale flipper, bat wing).
- Shows common ancestry even if the species are now very different.
- Vestigial structures (like the human tailbone) are leftovers from our evolutionary past.
🧪 4. Biochemical Data
- DNA and protein sequences are compared across species.
- The more similar the DNA or amino acid sequences, the more closely related the species are.
- The universal genetic code (same 4 bases, same codons) is strong evidence that all life shares a common origin.
➗ 5. Mathematical Data
- Hardy-Weinberg equations help measure if a population is evolving.
- Statistical models and simulations show how traits spread or disappear.
- Allele frequency changes can be tracked and predicted using math.
🧠 Summary:
Evolution isn’t just a “story” – it’s backed by hard data from geography, geology, biology, chemistry, and math. All these fields independently confirm that life on Earth has evolved and continues to evolve over time.
7.6.B – How Morphological, Biochemical & Geological Data Show Evolution Over Time
🎯 What’s the Big Idea?
We know organisms have changed over time but how do we know?
Scientists use 3 main types of evidence to prove this:
- Morphological (structure)
- Biochemical (DNA/proteins)
- Geological (fossils & rock layers)
All three help us trace back how life evolved and show how species are connected through common ancestry.
🔎 1. Morphological Evidence (Body Structures)
Definition: This is about the form and structure of organisms especially comparing bones, limbs, and organs across species.
- Homologous structures = same structure, different function (e.g., human arm, bat wing, whale flipper)
- Means: These species likely evolved from a common ancestor but adapted to different environments.
- Vestigial structures = parts that no longer serve a function but are still there
- Like: human appendix or tailbone, or pelvic bones in whales
- Shows: These were useful in ancestral species but became less important over time.
🧪 2. Biochemical Evidence (DNA & Proteins)
- DNA = universal code → All living things use the same 4 bases (A, T, C, G)
- Shows: All life shares a common origin.
- The more similar the DNA or protein sequences, the closer the relationship.
- Example: Humans and chimpanzees share over 98% of their DNA!
- This proves: We diverged from a common ancestor not too long ago (in evolutionary time).
- Scientists also compare amino acid sequences in proteins like hemoglobin or cytochrome c to build evolutionary trees (phylogenies).
⛰️ 3. Geological Evidence (Fossils & Rock Layers)
- Fossils show physical remains of organisms that lived long ago.
- By comparing fossils from different layers of Earth, we can see changes in form over time – like the evolution of horses, whales, or humans.
- Older fossils are found in deeper layers; newer ones are closer to the surface.
- Transitional fossils (like Archaeopteryx or Tiktaalik) show features of two major groups (e.g., reptiles & birds, or fish & amphibians) – proof of gradual evolution.
🧠 Final Thoughts:
- Organisms have changed over time
- They are related through common ancestry
- Evolution is a process that leaves evidence behind in bodies, genes, and rocks
7.6.B.1 – How Molecular, Morphological & Genetic Evidence Helps Us Understand Evolution
🎯 Main Idea:
We can better understand how life has evolved by looking at both living (extant) and extinct organisms through DNA, structures, and fossils. These clues help scientists trace evolutionary history and prove common ancestry.
🧬 1. Fossil Dating: How Do We Know How Old Fossils Are?
Fossils are super important but just finding them isn’t enough. We need to know how old they are to place them in the evolutionary timeline.
⏳ Ways to Date Fossils:
- Rock Layers (Relative Dating): Fossils found in deeper layers are older. This helps us see the order of appearance of organisms.
- Radioactive Isotope Decay (Absolute Dating):
- Example: Carbon-14 dating
- Scientists know how fast certain isotopes decay, so they calculate the fossil’s age based on how much isotope is left.
- Works best on fossils up to ~50,000 years old.
- Geographic Data: Fossils found in certain continents or terrains help us understand where organisms lived. This ties into continental drift and how species migrated or evolved in isolation.
🦴 2. Morphological Homologies & Vestigial Structures: Body Clues from Evolution
- Homologous Structures: Body parts that look similar in structure but may have different functions.
- Example: human arm 🧍♂️, bat wing 🦇, whale flipper 🐋
- These show that species had a common ancestor but evolved differently due to environment.
- Vestigial Structures: Leftover body parts that don’t serve a clear function anymore.
- Examples: human appendix, tailbone, wisdom teeth
- These suggest that ancestors used them, but we’ve evolved beyond their need.
💡 Why This Matters:
- Life on Earth has evolved gradually
- Species are connected by shared ancestors
- Evolution is real and leaves behind physical and molecular fingerprints
7.6.B.2 – DNA & Protein Sequences as Evidence for Evolution
🧠 Key Idea:
The more similar two organisms are at the DNA or protein level, the more closely related they are. This gives strong molecular evidence for evolution and common ancestry.
🧬 DNA Sequence Comparison:
- All living things use the same genetic code (A, T, C, G).
- When scientists compare specific gene sequences (like the gene for insulin or cytochrome c), they find:
- Humans & chimps = ~98% similar
- Humans & mice = ~85%
- Humans & yeast = less, but still some similarity!
- The more similarities, the more recent the common ancestor.
🧪 Protein (Amino Acid) Sequence Comparison:
- Proteins are made from amino acids, and their order is coded by DNA.
- If two organisms have similar amino acid sequences in the same protein, that means their genes are similar too.
- Example: Cytochrome c (used in cellular respiration) is nearly identical in humans and chimpanzees.
- This suggests conserved genes that have been passed down from a shared ancestor.
🧬💥 Mutation Clues:
- Over time, DNA mutates slowly. These small changes add up.
- By counting the number of differences, scientists can estimate how long-ago species split from a common ancestor.
- This is the basis of a molecular clock.
🔗 So What Does This Prove?
- Organisms that seem different physically might still be closely related genetically.
- DNA and proteins act like “evolution’s receipts” – proving who’s related to who.