Relatedness of Species

The term relatedness refers to how recently a particular species split from a common ancestor. Understanding the evolutionary history of species and the degree of relatedness among organisms is a key focus of evolutionary biology.

Scientists in evolutionary biology use various methods to determine how closely species are related to each other or to a common ancestor. These methods include:

• Comparative anatomy or vestigial structures: These suggest a shared common ancestor
• Molecular comparisons of DNA and amino acid sequences: Relatedness can be inferred based on the degree of similarity shared between species.
• Constructing phylogenetic trees: These trees represent evolutionary relationships among species and illustrate how species diverged from common ancestors over time.

The more similar two species are in their structure, DNA sequence or amino acid sequence, the more closely related they are.

This resource revises relatedness of species and within relatedness of species there are 3 key concepts:

• structural morphology
• molecular homology
• phylogenetic trees.

To determine if this resource will benefit you, start by answering the following questions:

• Are you able to describe what homologous and vestigial structures are and how they can provide evidence for relatedness between species?
• Do you understand how comparing amino acid sequences and DNA sequences can be used to determine relatedness between species?
• Can you describe what a phylogenetic tree is and how it depicts relatedness between species?

The answers to these questions are provided on the following pages. Use this resource to refresh your memory, reinforce your understanding of these concepts, and prepare more effectively for university-level learning.

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