Common Ancestry in AP Biology
Common ancestry is a fundamental concept in evolutionary biology, explaining how all life on Earth shares a common genetic origin. This idea is supported by fossil records, molecular evidence, homologous structures, embryology, and phylogenetics.
In this guide, we’ll explore the evidence supporting common ancestry, the role of natural selection, and how this topic appears on the AP Biology exam.
1. What Is Common Ancestry?
Common ancestry refers to the shared evolutionary history of organisms. It suggests that all species evolved from a universal common ancestor, diverging over time through speciation and natural selection.
Key Points:
- All life shares DNA, RNA, and proteins, indicating a common origin.
- Evolutionary relationships are traced through phylogenetic trees and cladograms.
- Evidence comes from morphological, genetic, and fossil data.
2. Evidence Supporting Common Ancestry
A. Fossil Record
Fossils provide physical evidence of ancient organisms, showing gradual changes over time.
- Transitional fossils (e.g., Tiktaalik) link fish to tetrapods.
- Fossil layers indicate evolutionary progression.
B. Homologous and Vestigial Structures
- Homologous structures (e.g., vertebrate forelimbs) show common ancestry despite different functions.
- Vestigial structures (e.g., human tailbone, whale pelvis) indicate evolutionary remnants.
C. Molecular Evidence
- DNA and protein similarities reveal genetic connections.
- Highly conserved genes (e.g., Hox genes) regulate development in diverse species.
- Cytochrome c and ribosomal RNA provide evolutionary comparisons.
D. Embryological Similarities
- Early embryonic development in vertebrates shows similar structures, suggesting a shared ancestor.
E. Biogeography
- Geographic distribution of species supports evolution (e.g., Darwin’s finches).
3. Phylogenetics and Cladistics
Phylogenetics studies evolutionary relationships through cladograms and phylogenetic trees.
Key Concepts:
- Cladograms show evolutionary branching based on shared traits.
- Outgroups help determine ancestral vs. derived traits.
- Maximum parsimony principle favors the simplest evolutionary pathway.
4. Common Ancestry & Natural Selection
Darwin’s theory of natural selection explains how species evolve from common ancestors through adaptation and survival.
Key Points:
- Descent with modification: Traits change over generations.
- Genetic variation arises from mutations and recombination.
- Selective pressures drive evolutionary changes.
5. AP Biology Exam Tips for Common Ancestry
To ace questions on common ancestry in the AP Bio exam, focus on:
- Recognizing evolutionary relationships in phylogenetic trees.
- Interpreting DNA and protein sequence similarities for relatedness.
- Understanding fossil evidence and morphological comparisons.
- Applying natural selection principles to evolution scenarios.
Practice Question:
A scientist analyzes DNA sequences of three species and finds that species A and B share 95% of their genome, while species C shares only 80%. What does this suggest about their evolutionary relationships?
👉 Answer: Species A and B have a more recent common ancestor than species C, as genetic similarity indicates closer evolutionary ties.
Common Ancestry for the AP Bio Exam CONC
Understanding common ancestry is crucial for AP Biology success. By mastering fossil evidence, phylogenetics, and molecular data, you’ll be well-prepared for exam questions on evolutionary biology.
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