I.
Biology and Society: The Sixth Mass Extinction
1. Over the past 540 million years, the fossil record reveals five periods of extinction
when 50–90% of living species suddenly died out.
2. Our current rate of extinction, over the past 400 years, indicates that we may be
living in, and contributing to, the sixth mass extinction period.
3. Mass extinctions pave the way for the evolution of new and diverse forms, but it
takes millions of years for Earth to recover.
II. The Origin of Species
1. When Darwin visited the Galápagos Islands, he realized that he was visiting a place
of origins.
a. Although the volcanic islands were geologically young, they were home to many
plants and animals known nowhere else in the world.
b. Darwin thought it unlikely that all of these species could have been among the
original colonists of the islands.
2. In the 150 years since the publication of Darwin’s book On the Origin of Species by
Means of Natural Selection, new discoveries and technological advances have given
scientists a wealth of new information about the evolution of life.
3. The diversity of life evolved through speciation, the process in which one species
splits into two or more species.
A. What Is a Species?
1. Species is a Latin word meaning
a. “kind” or
b. “appearance.”
2. The biological species concept defines a species as “A group of populations
whose members have the potential to interbreed with one another in nature to
produce fertile offspring.”
3. The biological species concept cannot be applied in all situations, including
a. fossils and
b. asexual organisms.
4. Some other definitions of species are based on
a. measurable physical traits,
b. the use of ecological resources, or
c. unique adaptations to particular roles in a biological community.
B. Reproductive Barriers between Species
1. Prezygotic barriers prevent mating or fertilization between species.
2. Prezygotic barriers include
a. temporal isolation,
b. habitat isolation,
c. behavioral isolation,
d. mechanical isolation, and
e. gametic isolation.
3. Postzygotic barriers operate if
a. interspecies mating occurs and
b. hybrid zygotes form.
4. Postzygotic barriers include
a. reduced hybrid viability,
b. reduced hybrid fertility, and
c. hybrid breakdown.
C. Mechanisms of Speciation
1. A key event in the potential origin of a species occurs when a population is somehow
cut off from other populations of the parent species.
2. Species can form by
a. allopatric speciation, due to geographic isolation, or
b. sympatric speciation, without geographic isolation.
3. Allopatric Speciation
4. Geologic processes can
a. fragment a population into two or more isolated populations and
b. contribute to allopatric speciation.
5. Speciation occurs with the evolution of reproductive barriers between
a. the isolated population and
b. its parent population.
6. Even if the two populations should come back into contact at some later time, the
reproductive barriers will keep them as separate species.
7. Sympatric Speciation.
8. Sympatric speciation occurs in populations that live in the same geographic area.
9. An accident during cell division that results in an extra set of chromosomes is a
common route to sympatric speciation in plants.
10. any polyploid species arise from the hybridization of two parent species.
11. any domesticated plants are the result of sympatric speciation, including
a. oats,
b. potatoes,
c. bananas,
d. peanuts,
e. apples,
f. coffee, and
g. wheat.
D. What Is the Tempo of Speciation?
1. There are two contrasting patterns for the pace of evolution:
a. the gradual pattern, in which big changes (speciations) occur by the steady
accumulation of many small changes and
b. the punctuated equilibria pattern, in which there are
i.
long periods of little apparent change, (equilibria) interrupted (punctuated) by
ii. relatively brief periods of rapid change.
III. The Evolution of Biological Novelty
1. What accounts for the dramatic differences between dissimilar groups?
A. Adaptation of Old Structures for New Functions
1. Birds
a. are derived from a lineage of earthbound reptiles and
b. evolved flight from flightless ancestors.
2. An exaptation is
a. a structure that evolves in one context but becomes adapted for another function
and
b. a type of evolutionary remodeling.
3. Exaptations can account for the evolution of novel structures.
4. Bird wings are modified forelimbs that were previously adapted for non-flight
functions, such as
a. thermal regulation,
b. courtship displays, and/or
c. camouflage.
5. The first flights may have been only glides or extended hops as the animal pursued
prey or fled from a predator.
B. Evo-Devo: Development and Evolutionary Novelty
1. Evo-devo, evolutionary developmental biology, is the study of the evolution of
developmental processes in multicellular organisms.
2. Homeotic genes are master control genes that regulate
a. the rate,
b. timing, and
c. spatial pattern of changes in an organism’s form as it develops from a zygote into
an adult.
3. Mutations in homeotic genes can profoundly affect body form.
4. Paedomorphosis
a. is the retention into adulthood of features that were solely juvenile in ancestral
species and
b. has occurred in the evolution of
i.
axolotl salamanders and
ii. humans.
IV. Earth History and Macroevolution
1. Macroevolution is closely tied to the history of Earth.
A. Geologic Time and the Fossil Record
1. The fossil record is
a. the sequence in which fossils appear in rock strata and
b. an archive of macroevolution.
2. Geologists have established a geologic time scale that divides Earth’s history into a
consistent sequence of geologic periods.
3. Fossils are reliable chronological records only if we can determine their ages, using
a. the relative age of fossils, revealing the order in which groups of species evolved,
and/or
b. the absolute age of fossils, requiring other methods such as radiometric dating.
4. Radiometric dating
a. is the most common method for dating fossils,
b. is based on the decay of radioactive isotopes, and
c. helped establish the geologic time scale.
B. Plate Tectonics and Macroevolution
1. The continents are not locked in place.
a. Continents drift about Earth’s surface on plates of crust floating on a flexible layer
of hot, underlying material called the mantle.
2. Japan sits atop four different plates.
a. A tsunami, caused by an earthquake off the coast of Japan, resulted in the
disaster of March 2011.
b. Frequent earthquakes occur as the plates move and bump against each other.
3. About 250 million years ago,
a. plate movements formed the supercontinent Pangaea,
b. the total amount of shoreline was reduced,
c. ocean basins increased in depth,
d. sea levels dropped,
e. the dry continental interior increased in size, and
f. many extinctions occurred.
4. About 180 million years ago,
a. Pangaea began to break up,
b. large continents drifted increasingly apart,
c. climates changed, and
d. the organisms of the different biogeographic realms diverged.
5. Plate tectonics helps to explain
a. why Mesozoic reptiles in Ghana (West Africa) and Brazil look so similar and
b. how marsupials were free to evolve in isolation in Australia.
C. Mass Extinctions and Explosive Diversifications of Life
1. The fossil record reveals that five mass extinctions have occurred over the last
540 million years.
2. The Permian mass extinction
a. occurred at about the time the merging continents formed Pangaea (250 million
years ago) and
b. claimed about 96% of marine species.
3. The Cretaceous extinction
a. occurred at the end of the cretaceous period, about 65 million years ago,
b. included the extinction of all the dinosaurs except birds, and
c. permitted the rise of mammals.
D. The Process of Science: Did a Meteor Kill the Dinosaurs?
1. The fossil record reveals that five mass extinctions have occurred over the last
540 million years.
2. In each of these events, 50% or more of Earth’s species died out.
3. Of all the mass extinctions, those marking the ends of the Permian and Cretaceous
periods have been the most intensively studied.
4. Observation: About 65 million years ago, the fossil record shows that
a. the climate cooled,
b. seas were receding,
c. many plant species died out,
d. dinosaurs (except birds) became extinct, and
e. a thin layer of clay rich in iridium was deposited.
5. Question: Is the iridium layer the result of fallout from a huge cloud of dust that
billowed into the atmosphere when a large meteor or asteroid hit Earth?
6. Hypothesis: The mass extinction 65 million years ago was caused by the impact of
an extraterrestrial object.
7. Prediction: A huge impact crater of the right age should be found somewhere on
Earth’s surface.
8. Results: Near the Yucatán Peninsula, a huge impact crater was found that
a. dated from the predicted time,
b. was about the right size, and
c. was capable of creating a cloud that could have blocked enough sunlight to
change the Earth’s climate for months.
V. Classifying the Diversity of Life
1. Systematics focuses on
a. classifying organisms and
b. determining their evolutionary relationships.
2. Taxonomy is the
a. identification,
b. naming, and
c. classification of species.
3. Systematics includes taxonomy.
A. Some Basics of Taxonomy
1. Scientific names ease communication by
a. unambiguously identifying organisms and
b. making it easier to recognize the discovery of a new species.
2. Carolus Linnaeus (1707–1778) proposed the current taxonomic system based upon
a
a. two-part name for each species and
b. hierarchical classification of species into broader groups of organisms.
3. Naming Species
4. Each species is assigned a two-part Latinized name or binomial, consisting of
a. the genus and
b. a name unique for each species.
5. The scientific name for humans is Homo sapiens,
a. a two part name, italicized,
b. given a Latin ending, and
c. with the first letter of the genus capitalized.
6. Hierarchical Classification.
7. Species that are closely related are placed into the same genus.
8. The taxonomic hierarchy extends to progressively broader categories of
classification, from genus to
a. family,
b. order,
c. class,
d. phylum,
e. kingdom, and
f. domain.
B. Classification and Phylogeny
1. The goal of systematics is to have classification reflect evolutionary relationships.
2. Biologists use phylogenetic trees to
a. depict hypotheses about the evolutionary history of species and
b. reflect the hierarchical classification of groups nested within more inclusive
groups.
3. Sorting Homology from Analogy
4. Homologous structures
a. reflect variations of a common ancestral plan and
b. are one of the best sources of information used to
i.
develop phylogenetic trees and
ii. classify organisms according to their evolutionary history.
5. Convergent evolution involves superficially similar structures from different
evolutionary branches that result from natural selection shaping analogous
adaptations.
6. Similarity due to convergence is called analogy, not homology.
7. To develop phylogenetic trees and classify organisms according to their evolutionary
history, we use only homologous similarities.
8. Molecular Biology as a Tool in Systematics.
9. Molecular systematics
a. compares nucleotide and amino acid sequences between organisms and
b. can reveal evolutionary relationships.
10. The more recently two species have branched from a common ancestor, the more
similar their nucleotide and amino acid sequences should be.
11. Some fossils are preserved in such a way that DNA fragments can be extracted for
comparison with living organisms.
C. The Cladistic Revolution
1. In cladistics, organisms are grouped by common ancestry.
2. A clade consists of an ancestral species and all its evolutionary descendants and
forms a distinct branch in the tree of life.
3. Cladistics is based on the Darwinian concept of “descent with modification from a
common ancestor.”
4. To identify clades, scientists compare an ingroup with an outgroup.
5. Cladistics has changed the traditional classification of some organisms, including the
relationships between
a. dinosaurs,
b. birds,
c. crocodiles,
d. lizards, and
e. snakes.
D. Classification: A Work in Progress
1. Phylogenetic trees are hypotheses about evolutionary history.
2. Linnaeus divided all known forms of life between the plant and animal kingdoms.
a. this two-kingdom system prevailed in biology for over 200 years.
3. In the mid-1900s, the two-kingdom system was replaced by a five-kingdom system
that
a. placed all prokaryotes in one kingdom and
b. divided the eukaryotes among four other kingdoms.
4. In the late 1900s, molecular studies and cladistics led to the development of a
three-domain system, recognizing
a. two domains of prokaryotes (Bacteria and Archaea) and
b. one domain of eukaryotes (Eukarya).
E. Evolution Connection: Rise of the Mammals
1. Mass extinctions
a. have repeatedly occurred throughout Earth’s history and
b. were followed by a period of evolutionary change.
2. Fossil evidence indicates that
a. mammals first appeared about 180 million years ago but
b. the number of mammalian species
i.
remained steady and low in number until about 65 million years ago and
ii. greatly increased after most of the dinosaurs became extinct.
3. Throughout the process of evolution by natural selection, this pattern of death and
renewal is repeated throughout the history of life on Earth.