1. Tracing Evolutionary History
Chapter 15
Tracing Evolutionary History

2. MAJOR EVENTS IN THE HISTORY OF LIFE
MAJOR EVENTS IN THE HISTORY OF LIFE
© 2012 Pearson Education, Inc. 2

3. Life’s Calendar

4. Multicellular eukaryotes
Figure 15.4
Archaean
eon
Proterozoic
eon
Phanerozoic
eon
Colonization
of land
Animals
Multicellular eukaryotes
Single-celled eukaryotes
Atmospheric oxygen
Origin
of Earth
Prokaryotes
4.6
Figure 15.4 Some key events in the history of life on Earth 4 3 2 1
Present
Billions of years ago 4

5. 15.4 The origins of single-celled and multicelled organisms and the colonization of land were key events in life’s history
Prokaryotes lived alone on Earth for 1.5 billion years, from 3.5 to 2 billion years ago.
During this time, prokaryotes transformed the atmosphere.
Prokaryotic photosynthesis produced oxygen that enriched the water and atmosphere of Earth.
Anaerobic and aerobic cellular respiration allowed prokaryotes to flourish.
Student Misconceptions and Concerns
Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular animal life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective.  
Teaching Tips
1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. This is consistent with the gradual evolution of life on Earth.
2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods.
© 2012 Pearson Education, Inc. 5

6. 15.4 The origins of single-celled and multicelled organisms and the colonization of land were key events in life’s history
The oldest fossils of eukaryotes are about 2.1 billion years old.
The common ancestor of all multicellular eukaryotes lived about 1.5 billion years ago.
The oldest fossils of multicellular eukaryotes are about 1.2 billion years old.
The first multicellular plants and fungi began to colonize land about 500 million years ago.
Student Misconceptions and Concerns
Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular animal life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective.  
Teaching Tips
1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. This is consistent with the gradual evolution of life on Earth.
2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods.
© 2012 Pearson Education, Inc. 6

7. 15.4 The origins of single-celled and multicelled organisms and the colonization of land were key events in life’s history
Humans diverged from other primates about 6 to 7 million years ago.
Our species, Homo sapiens, originated about 195,000 years ago.
If the Earth’s history were compressed into an hour, humans appeared less than 0.2 seconds ago!
Student Misconceptions and Concerns
Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular animal life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective.  
Teaching Tips
1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. This is consistent with the gradual evolution of life on Earth.
2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods.
© 2012 Pearson Education, Inc. 7

8. Larger Cells and Organisms Need More Oxygen
More O2 allows for CR and aerobic metabolism = greater ATP yield!! 8

9. Molecular Homologies Provide Greatest Evidence for Life’s Common Ancestor
All living organisms share many biochemical and developmental pathways:
DNA --> RNA --> Protein
Same genetic code
Transcription/translation/replication processes same
Glycolysis and cellular respiration similar
Many genes are amazingly similar
About 99% of the genes of humans and mice are homologous.
About 50% of human genes are homologous with those of yeast.
Teaching Tips
1. The National Center for Science Education is an organization working to support the teaching of evolution and defend it against sectarian attack. Its website, contains a great deal of useful information.
2. 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.
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10. Three Domain System
Molecular homologies have unveiled a new organization to life’s history.
Comparison of rRNA gene sequences by Carl Woese
Remember, rRNA gene sequences allow for comparison of long-distance relationships
Biologists currently recognize a three-domain system consisting of
two domains of prokaryotes: Bacteria and Archaea, and
one domain of eukaryotes called Eukarya including
fungi, protists, plants, animals
Teaching Tips
1. The National Center for Science Education is an organization working to support the teaching of evolution and defend it against sectarian attack. Its website, contains a great deal of useful information.
2. The authors reference Modules and for information on horizontal gene transfer. If this module was not previously addressed, consider covering it in your final discussion of the early evolution of life.
3. For some students, the discussion of the ambiguous relationships of early life and the three domains can be unsettling. Students who expect clear answers and sharp definitions from science may be uncomfortable with such ambiguity.
© 2012 Pearson Education, Inc. 10

11. Table 16.7 Differences between the domains Bacteria, Archaea, and Eukarya11

12. Most recent common ancestor of all living things
Figure 15.19A 1
Most recent common ancestor of all living things 2
Gene transfer between mitochondrial ancestor
and ancestor of eukaryotes 3
Gene transfer between chloroplast ancestor
and ancestor of green plants
Bacteria 3 2 1
Eukarya
Figure 15.19A Two major episodes of horizontal gene transfer in the history of life (dates are uncertain)
Archaea 4 3 2 1
Billions of years ago 12

13. Figure 1.4 The Tree of Life

14. Implications of Updated Tree of Life
Bacteria and Archaea diverged very early in the evolutionary history of life
Archaea are more closely related to eukaryotes than to bacteria.
Eukarya diverged from line of Archaea
Several endosymbiotic events lead to evolution of eukaryotes
Mitochrondria acquired from aerobic bacteria
Chloroplast from photosynthetic bacteria
Mitochondria acquired first; 1st eukaryotes heterotrophic
Multicellularity in eukaryotes arose multiple times (convergent evolution)
Teaching Tips
1. The National Center for Science Education is an organization working to support the teaching of evolution and defend it against sectarian attack. Its website, contains a great deal of useful information.
2. The authors reference Modules and for information on horizontal gene transfer. If this module was not previously addressed, consider covering it in your final discussion of the early evolution of life.
3. For some students, the discussion of the ambiguous relationships of early life and the three domains can be unsettling. Students who expect clear answers and sharp definitions from science may be uncomfortable with such ambiguity.
© 2012 Pearson Education, Inc. 14

15. Endosymbiosis theory
Mitochondria & chloroplasts were once free living bacteria
engulfed by ancestral eukaryote
Endosymbiont
cell that lives within another cell (host)
as a partnership
evolutionary advantage for both
one supplies energy
the other supplies raw materials & protection
Lynn Margulis
From hypothesis to theory!
Paradigm shifting ideas in evolutionary biology.
Lynn Margulis
U of M, Amherst

16. Evolution of eukaryotes
Endosymbiosis theory
Evolution of eukaryotes