20: Phylogenies and the History of Life - Biology

20: Phylogenies and the History of Life - Biology

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20: Phylogenies and the History of Life

20: Phylogenies and the History of Life - Biology

This bee and Echinacea flower (Figure 1) could not look more different, yet they are related, as are all living organisms on Earth. By following pathways of similarities and changes—both visible and genetic—scientists seek to map the evolutionary past of how life developed from single-celled organisms to the tremendous collection of creatures that have germinated, crawled, floated, swam, flown, and walked on this planet.

Figure 1. The life of a bee is very different from the life of a flower, but the two organisms are related. Both are members the domain Eukarya and have cells containing many similar organelles, genes, and proteins. (credit: modification of work by John Beetham)

Learning Objectives

  • Discuss the components and purpose of a phylogenetic tree
  • List the different levels of the taxonomic classification system
  • Compare homologous and analogous traits
  • Discuss the purpose of cladistics
  • Identify different perspectives and criticisms of the phylogenetic tree

Stuents watch the video about how to interpret phylogenetic trees here.

Instructors then administer one or both of these quizzes. This PDF contains both the two quizzes and their answer keys.

This is a lab activity called the Caminalcule Evolution Lab. In Part 1, students classify 14 living hypothetical species based on pictures and then create a small phylogenetic tree for them. In Part 2, they create a larger tree for 58 fossils species and look for patterns such as vestigial traits and convergence. Included in this link are instructor tips for both majors and nonmajors.

Find the correct answers to the end of the chapter &ldquoReview Questions.&rdquo Note the page number on which you found the answer. Be prepared to share and explain your answers in a group setting.

Answer the end of the chapter &ldquoCritical Thinking Questions.&rdquo Note the page number on which you found the answer. Be prepared to share and explain your answers in a group setting.


This bee and Echinacea flower (Figure 20.1) could not look more different, yet they are related, as are all living organisms on Earth. By following pathways of similarities and changes—both visible and genetic—scientists seek to map the evolutionary past of how life developed from single-celled organisms to the tremendous collection of creatures that have germinated, crawled, floated, swum, flown, and walked on this planet.

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    • Book title: Biology 2e
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    Visit this website to classify three organisms—bear, orchid, and sea cucumber—from kingdom to species. To launch the game, under Classifying Life, click the picture of the bear or the Launch Interactive button.

    Recent genetic analysis and other advancements have found that some earlier phylogenetic classifications do not align with the evolutionary past therefore, changes and updates must be made as new discoveries occur. Recall that phylogenetic trees are hypotheses and are modified as data becomes available. In addition, classification historically has focused on grouping organisms mainly by shared characteristics and does not necessarily illustrate how the various groups relate to each other from an evolutionary perspective. For example, despite the fact that a hippopotamus resembles a pig more than a whale, the hippopotamus may be the closest living relative of the whale.

    Start Quiz: Biology 20 Phylogenies & the History of Life

    This NASA image is a composite of several satellite-based views of Earth. To make the whole-Earth image, NASA scientists combine observations of different parts of the planet. (credit: NASA/GSFC/NOAA/USGS)

    Viewed from space, Earth offers no clues about the diversity of life forms that reside there. The first forms of life on Earth are thought to have been microorganisms that existed for billions of years in the ocean before plants and animals appeared. The mammals, birds, and flowers so familiar to us are all relatively recent, originating 130 to 200 million years ago. Humans have inhabited this planet for only the last 2.5 million years, and only in the last 200,000 years have humans started looking like we do today.

    Chapter 20: Phylogenies and the History of Life MCQ Multiple Choices Questions Quiz Test Bank

    20.1 Organizing Life on Earth

    20.2 Determining Evolutionary Relationships

    20.3 Perspectives on the Phylogenetic Tree

    Name: Biology 20 Phylogenies & the History of Life
    Download URL: Download MCQ Quiz PDF eBook
    Book Size: 12 Pages
    Copyright Date: 2015
    Language: English US
    Categories: Educational Materials

    Question: What do scientists in the field of systematics accomplish?

    discover new fossil sites

    organize and classify organisms

    communicate among field biologists

    Question: Why do scientists apply the concept of maximum parsimony?

    to decipher accurate phylogenies

    to eliminate analogous traits

    to identify mutations in DNA codes

    Question: What is used to determine phylogeny?

    Question: Particles that transfer genetic material from one species to another, especially in marine prokaryotes:

    Question: What do scientists use to apply cladistics?

    Question: Which statement about the taxonomic classification system is correct?

    There are more domains than kingdoms.

    Kingdoms are the top category of classification.

    Classes are divisions of orders.

    Subspecies are the most specific category of classification.

    Question: The transfer of genes by a mechanism not involving asexual reproduction is called:

    Question: What is true about organisms that are a part of the same clade?

    They all share the same basic characteristics.

    They evolved from a shared ancestor.

    They usually fall into the same classification taxa.

    They have identical phylogenies.

    Question: What does the trunk of the classic phylogenetic tree represent?

    pool of ancestral organisms

    Question: Which statement about analogies is correct?

    They occur only as errors.

    They are synonymous with homologous traits.

    They are derived by similar environmental constraints.

    They are a form of mutation.

    Question: On a phylogenetic tree, which term refers to lineages that diverged from the same place?


    Our editors will review what you’ve submitted and determine whether to revise the article.

    Phylogeny, the history of the evolution of a species or group, especially in reference to lines of descent and relationships among broad groups of organisms.

    Fundamental to phylogeny is the proposition, universally accepted in the scientific community, that plants or animals of different species descended from common ancestors. The evidence for such relationships, however, is nearly always incomplete, for the vast majority of species that have ever lived are extinct, and relatively few of their remains have been preserved in the fossil record. Most phylogenies therefore are hypotheses and are based on indirect evidence. Different phylogenies often emerge using the same evidence. Nevertheless, there is universal agreement that the tree of life is the result of organic descent from earlier ancestors and that true phylogenies are discoverable, at least in principle.

    Ring of Life Models

    Others have proposed abandoning any tree-like model of phylogeny in favor of a ring structure, the so-called “ring of life ” (Figure) a phylogenetic model where all three domains of life evolved from a pool of primitive prokaryotes. Lake, again using the conditioned reconstruction algorithm, proposes a ring-like model in which species of all three domains—Archaea, Bacteria, and Eukarya—evolved from a single pool of gene-swapping prokaryotes. His laboratory proposes that this structure is the best fit for data from extensive DNA analyses performed in his laboratory, and that the ring model is the only one that adequately takes HGT and genomic fusion into account. However, other phylogeneticists remain highly skeptical of this model.

    According to the “ring of life” phylogenetic model, the three domains of life evolved from a pool of primitive prokaryotes.

    In summary, the “tree of life” model proposed by Darwin must be modified to include HGT. Does this mean abandoning the tree model completely? Even Lake argues that all attempts should be made to discover some modification of the tree model to allow it to accurately fit his data, and only the inability to do so will sway people toward his ring proposal.

    This doesn’t mean a tree, web, or a ring will correlate completely to an accurate description of phylogenetic relationships of life. A consequence of the new thinking about phylogenetic models is the idea that Darwin’s original conception of the phylogenetic tree is too simple, but made sense based on what was known at the time. However, the search for a more useful model moves on: each model serving as hypotheses to be tested with the possibility of developing new models. This is how science advances. These models are used as visualizations to help construct hypothetical evolutionary relationships and understand the massive amount of data being analyzed.

    Phylogenetic Trees

    Both of these phylogenetic trees shows the relationship of the three domains of life—Bacteria, Archaea, and Eukarya—but the (a) rooted tree attempts to identify when various species diverged from a common ancestor while the (b) unrooted tree does not. (credit a: modification of work by Eric Gaba)

    The root of a phylogenetic tree indicates that an ancestral lineage gave rise to all organisms on the tree. A branch point indicates where two lineages diverged. A lineage that evolved early and remains unbranched is a basal taxon. When two lineages stem from the same branch point, they are sister taxa. A branch with more than two lineages is a polytomy.

    The diagrams above can serve as a pathway to understanding evolutionary history. The pathway can be traced from the origin of life to any individual species by navigating through the evolutionary branches between the two points. Also, by starting with a single species and tracing back towards the "trunk" of the tree, one can discover that species' ancestors, as well as where lineages share a common ancestry. In addition, the tree can be used to study entire groups of organisms.

    Another point to mention on phylogenetic tree structure is that rotation at branch points does not change the information. For example, if a branch point was rotated and the taxon order changed, this would not alter the information because the evolution of each taxon from the branch point was independent of the other.

    Many disciplines within the study of biology contribute to understanding how past and present life evolved over time these disciplines together contribute to building, updating, and maintaining the “tree of life.” Information is used to organize and classify organisms based on evolutionary relationships in a scientific field called systematics . Data may be collected from fossils, from studying the structure of body parts or molecules used by an organism, and by DNA analysis. By combining data from many sources, scientists can put together the phylogeny of an organism since phylogenetic trees are hypotheses, they will continue to change as new types of life are discovered and new information is learned.

    Free Response

    Dolphins and fish have similar body shapes. Is this feature more likely a homologous or analogous trait?

    Dolphins are mammals and fish are not, which means that their evolutionary paths (phylogenies) are quite separate. Dolphins probably adapted to have a similar body plan after returning to an aquatic lifestyle, and, therefore, this trait is probably analogous.

    Why is it so important for scientists to distinguish between homologous and analogous characteristics before building phylogenetic trees?

    Phylogenetic trees are based on evolutionary connections. If an analogous similarity were used on a tree, this would be erroneous and, furthermore, would cause the subsequent branches to be inaccurate.

    Describe maximum parsimony.

    Maximum parsimony hypothesizes that events occurred in the simplest, most obvious way, and the pathway of evolution probably includes the fewest major events that coincide with the evidence at hand.

    Watch the video: Phylogeny, Speciation, Extinction and the History of Life on Earth Lecture Presentation (September 2022).