1. Tracing Evolutionary History
Chapter 15
Tracing Evolutionary History
Lecture by Joan Sharp

2. PHYLOGENY AND THE TREE OF LIFE
PHYLOGENY AND THE TREE OF LIFE
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3. Phylogeny is the evolutionary history of a species or group of species
15.14 Phylogenies are based on homologies in fossils and living organisms
Phylogeny is the evolutionary history of a species or group of species
Homologous and analogous relationships can be confusing for students. Simple explanations and concrete examples can serve as guides to understanding each process. Homologous relationships reflect modifications of “one form” to many “functions.” Analogous relationships reflect modifications of many “forms” for “one function.”
Student Misconceptions and Concerns
1. Homologous and analogous relationships can be confusing for students. Simple explanations and concrete examples can serve as guides to understanding each process. Homologous relationships reflect modifications of one form for many functions. Analogous relationships reflect modifications of many forms for one function.
Teaching Tips
1. Our hierarchical classification system is analogous to sorting mail first by zip code, then by street, house number, and finally individual name. Such a system of classification based upon hierarchical categories is also common in the military and many other places in our lives.
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4. There are several ways to define a species
Taxonomy is the branch of biology that names and classifies species and groups them into broader categories
Carolus Linnaeus developed the binomial system of naming organisms – binomial nomenclature
Student Misconceptions and Concerns
1. Students might have never considered how species are naturally kept separate and unique. Instead, students may consider species as fixed entities, especially the species to which they belong. To help ease students into the topic, consider pointing out that species do not reflect an even spectrum of diversity. Instead, there are many groups of clearly related organisms (owls, grasses, sharks, beetles, butterflies, trees, mushrooms, and bacteria, for example). Ask students to consider why such grouping exists. Could such grouping represent shared ancestry?
Teaching Tips
1. Before lecturing about species concepts, consider a short writing assignment. Have students work individually or in small groups, without the benefit of books, to define a species.
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5. 15.15 Systematics connects classification with evolutionary history
Taxonomists assign each species a binomial consisting of a genus and species name
Genera are grouped into progressively larger categories.
Each taxonomic unit is a taxon
Although Linnaeus recognized a hierarchical structure in the natural world, he had no natural explanation for the occurrence of such groups. One of Darwin’s greatest insights was to understand that these clusters reflect similarities due to shared ancestry and to propose a natural mechanism for the formation of new species and the generation of this diversity.
Student Misconceptions and Concerns
1. Students can be frustrated by the changing state of systematics. Some comfort can be offered by noting that this is true about many active areas of science. For example, scientists continue to learn more and revise advice regarding the causes, treatment, and prevention of heart disease and cancer.
2. Students might express concern over the need to learn scientific names, when common names already seem sufficient. Depending upon where you live, find some examples of common organisms with more than one common name. Fishermen are famous for the various names they assign to the same species, depending upon the geographic region where they fish. Have your students imagine the problems of using common names when communicating with someone in another language. Clearly, there are advantages to scientific names!
Teaching Tips
1. Although Linnaeus recognized a hierarchical structure in the natural world, he had no natural explanation for the occurrence of such groups. One might wonder why all life does not blend evenly from one form to another. One of Darwin’s greatest insights was to understand that these clusters reflect similarities due to shared ancestry, i.e., life itself is grouped into family trees. Furthermore, Darwin proposed a natural mechanism for the formation of new species and the generation of this diversity.
Copyright © 2009 Pearson Education, Inc.

6. Kingdom – Bacteria, Archeabacteria, Fungi, Protista, Plantae, Animalia
Phylum
Class
Order
Family
Genus
Species

7. Domains
Bacteria
Archaea
Eubacteria – have nucleus and orgnelles

8. Species: Felis catus Genus: Felis Family: Felidae Order: Carnivora
Class: Mammalia
Figure 15.15A Hierarchical classification of the domestic cat.
Phylum: Chordata
Kingdom: Animalia
Bacteria
Domain: Eukarya
Archaea

9. Order Family Genus Species Felis catus (domestic cat) Felidae Felis
Mephitis
mephitis
(striped skunk)
Mephitis
Carnivora
Mustelidae
Lutra
lutra
(European
otter)
Lutra
Figure 15.15B The relationship between classification and phylogeny.
Canis
latrans
(coyote)
Canidae
Canis
Canis
lupus
(wolf)

10. Practice with tables and diagrams

11. 15.16 Shared characters are used to construct phylogenetic trees
A phylogenetic tree is a hypothesis of evolutionary relationships within a group
Cladistics uses shared derived characters to group organisms into clades, including an ancestral species and all its descendents
An inclusive clade is monophyletic
Shared ancestral characters were present in ancestral groups
Consider that you are building a phylogenetic tree for tetrapods. The first tetrapod had a backbone, so the presence of a backbone is not useful in constructing a phylogenetic tree for tetrapods. By contrast, the amniotic egg and hair are traits that arose within the tetrapods. Both traits are useful in sorting out evolutionary relationships within tetrapods.
Student Misconceptions and Concerns
1. Students may struggle with many aspects of phylogenetic trees, including: (a) Students may not realize that each node/branch can be rotated to rearrange the groups without changing the nature of the relationships. For example, in Figure 15.16A, the position of the beaver and kangaroo can be reversed without changing any relationships represented in the phylogenetic tree. (b) The length of each branch is not meaningful and is not intended to be proportional to time. (c) The spacing between groups is not meaningful and does not denote the degree of divergence between them. Whether the tree is compressed or expanded in size, the information communicated in it remains the same.
Teaching Tips
1. Emphasize to students that phylogenetic trees are tentative hypotheses. As new data are collected, the hypotheses are modified or rejected outright.
Copyright © 2009 Pearson Education, Inc.

12. TAXA Duck-billed platypus Iguana Kangaroo Beaver Long gestation 11
CHARACTERS
Gestation 1 1
Figure 15.16A Constructing a phylogenetic tree using cladistics.
Hair, mammary
glands 1 1 1
Character Table

13. Hair, mammary glands Phylogenetic Tree
Iguana
Duck-billed
platypus
Hair, mammary glands
Kangaroo
Figure 15.16A Constructing a phylogenetic tree using cladistics.
Gestation
Beaver
Long gestation
Phylogenetic Tree

14. Lizards and snakes Crocodilians Pterosaurs Common ancestor of
dinosaurs,
and birds
Ornithischian
dinosaurs
Figure 15.16B A phylogenetic tree of reptiles.
Saurischian
dinosaurs
Birds

15. 15.17 An organism’s evolutionary history is documented in its genome
Molecular systematics compares nucleic acids or other molecules to infer relatedness of taxa
Scientists have sequenced more than 100 billion bases of nucleotides from thousands of species
Teaching Tips
1. Genetic relationships provide one strong line of evidence for the ancestral relationships of life. Fossils, anatomy, embryology, and biogeography can also be used to test these same relationships. Remind students that scientists prefer to use multiple lines of evidence to test hypotheses such as phylogenies.
For the BLAST Animation DNA and RNA Compared, go to Animation and Video Files.
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16. Lesser panda Procyonidae Raccoon Giant panda Spectacled bear Ursidae
Sloth bear
Sun bear
American
black bear
Asian black bear
Figure A phylogenetic tree based on molecular data.
Polar bear
Brown bear 35 30 25 20 15 10
Pleistocene
Oligocene
Miocene
Pliocene
Millions of years ago