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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 2. These questions will help guide your exploration and assist you in identifying the key concepts presented in this chapter.

  1. It is believed that all life on earth was derived from a single common ancestor. How do scientists determine how groups of organisms are related to one another?
  2. How has the use of DNA technology improved scientists' ability to determine evolutionary relationships?
  3. What are "shared derived features" and how do they differ from "convergent features" when determining evolutionary relationships?
  4. What can the construction of an evolutionary tree tell us about the paternal instincts of dinosaurs?
  5. How is the "wise man" (Homo sapiens) related to the "upright man" (Homo erectus) and the "handy man" (Homo habilus)?
  6. Why is the mushroom on your slice of pizza more closely related to you than it is to the green pepper that sits next to it?

A Guide to the Reading

When exploring the content in Chapter 2 for the first time, the following concepts typically give students the most difficulty.  For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas. 

Common Ancestor

Scientists known as systematists work to study the relationships among different groups of organisms. A graphical summary of their work can take the form of an "evolutionary tree". Just like a family tree, an evolutionary tree depicts relationships-- in this case, relationships between different species or groups of organisms. Descendants from a single ancestral species are depicted on the evolutionary tree as the tip of a branch. The most recent common ancestor of two divergent species is therefore represented on the tree by the point where one lineage branch joins another. While two groups of organisms may have many common ancestors, there can only be one most recent common ancestor, represented by the fork on the tree.

For more information on this concept, be sure to focus on:

  • In Section 2.1, Groups are related through their most recent common ancestor

Shared Derived Features vs. Convergent Features

Descendants from a common ancestor often share similar features. The unique features of an ancestral species (species that appeared first) which have been passed on to the divergent descendant species (species that appeared after the ancestral species) are referred to as shared derived features. Groups possessing such shared derived features are marked as a set of close relatives on an evolutionary tree. However, not all features shared between groups of organisms represent evolutionary relationships. Some features may have indeed evolved independently within two divergent groups of organisms. Such features are referred to as convergent features.

For more information on this concept, be sure to focus on:

  • In Section 2.1, Examining shared derived features helps determine the most recent common ancestor
  • In Section 2.1, Convergent features are similarities that do not indicate relatedness
  • Figure 2.2, Shared Derived Features Define Evolutionary Relationships
  • Figure 2.3, Misleading Convergent Features


TheIn the chapter, the Linnaean Hierarchy is described as a system adopted by scientists to classify organisms into specific taxonomic groups reflecting their relationships with other organisms within the hierarchy.  The original hierarchy described just two kingdoms: plants and animals.  Over  time, scientists have expanded this system to include upwards of eight kingdoms of organisms (your textbook adopts the widely used six-kingdom system).  Beyond this, scientists have recognized a need to create even larger groupings of organisms, referred to as a domain.  There are three proposed domains: Bacteria, Archaea, and Eukarya.  When reviewing the chapter, be sure to pay particular attention to the key differences which distinguish the Bacteria from the Archaea and how scientists have been able to use DNA to help support this proposed domain structure.

For more information on this concept, be sure to focus on:

  • In Section 2.3, A Classification System for Organizing Life: The Linnaean Hierarchy and Beyond

Horizontal Gene Transfer

In Chapter 2, the power of DNA technology to assist systematists in defining and refining evolutionary relationships between groups of organisms is highlighted with numerous examples.  However, the study of DNA has also raised new questions.  The text describes an example where studies revealed the presence of bacterial DNA within the cells of organisms from both the Archaean and Eukarya domains.  Dr. W. Ford Doolittle's theory of ”horizontal gene transfer” was developed to explain how organisms that diverged so long ago could share the same bacterial DNA.

For more information on this concept, be sure to focus on:

  • In Section 2.4, A surprising tangle can be found at the roots of the tree of life

Tying it all together

Several concepts presented in this chapter are revisited and discussed in greater detail in subsequent chapters, including:

Kingdoms of Life

  • Chapter 3 – in Section 3.1, The Major Groups in Context

Modern DNA Technologies

  • Chapter 12 – in Section 12.1, The Search for the Genetic Material
  • Chapter 15 – in Section 15.3, Applications of DNA Technology

Evolution and the Origin of Species

  • Chapter 16 – in Section 16.1, Biological Evolution: The Sum of Genetic Changes
  • Chapter 16 – in Section 16.4, Strong Evidence Shows that Evolution Happens
  • Chapter 19 – in Section 19.2, The History of Life on Earth

Mankind's Closest Relatives

  • Interlude D, Applying What We Learned: Humans and Evolution

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