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Eldra Solomon
Linda Berg
Diana W. Martin
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Chapter 18
(Sections 18.1-18.3)
Introduction to
Darwinian Evolution
Albia Dugger • Miami Dade College
Darwinian Evolution
• Charles Darwin (1809–1882) proposed that all species
currently living on our planet arose from earlier ones by a
process of gradual divergence or evolution
• Evidence supporting evolution: fossils, biogeography,
comparative anatomy, molecular biology, developmental
biology, and experimental studies of ongoing evolutionary
change
• Evolution is the cornerstone of biology because it links all life
sciences into a unified body of knowledge
Evolution
• Evolution is the accumulation of genetic changes within
populations over time
•
A population is a group of individuals of one species that live
in the same geographic area at the same time
• Eventually, two populations may diverge to such a degree
that they become different species (referred to as speciation)
• A species is a group of similar organisms that are capable of
interbreeding with one another
Two Perspectives on Evolution
• Microevolution
• The minor evolutionary changes of populations usually
viewed over a few generations
• Macroevolution
• The major evolutionary events usually viewed over a long
period, such as formation of different species from
common ancestors
Applications of Evolution
• Agriculture must deal with the evolution of pesticide
resistance in insects and other pests
• Medicine must respond to the rapid evolution of diseasecausing organisms such as bacteria and viruses
• Conservation management of rare and endangered species
uses evolutionary principles of population genetics
• Rapid evolution of microorganisms in polluted soils is used in
the field of bioremediation (clean up of hazardous-wastes)
18.2 PRE-DARWINIAN IDEAS
ABOUT EVOLUTION
LEARNING OBJECTIVE:
• Discuss the historical development of evolutionary
theory
Early History of
Evolutionary Theory
• Aristotle (384–322 bce)
• Visualized organisms as “moving toward a more perfect
state”
• Leonardo da Vinci (1452–1519)
• Correctly interpreted fossils as the remains of animals that
had existed in previous ages but had become extinct
• Jean Baptiste de Lamarck (1744–1829)
• Suggested that organisms pass traits they acquired during
their lifetimes to their offspring
KEY CONCEPTS 18.2
• Ideas about evolution originated long before Darwin’s time
18.3 DARWIN AND EVOLUTION
LEARNING OBJECTIVES:
• Explain the four premises of evolution by natural
selection as proposed by Charles Darwin
• Compare the modern synthesis with Darwin’s original
evolutionary theory
Voyage of HMS Beagle
• 1831: Darwin embarked on a 5-year exploratory cruise
around the world aboard the HMS Beagle
• He collected and cataloged thousands of plant and animal
specimens and kept notes of his observations
• He noticed similarities between animals and plants of the
Galápagos and those of South America, and saw differences
in reptiles and birds from one island to the next
Developing a Theory
• Upon returning home, Darwin attempted to develop a
explanation for the distribution of species among the islands
• He studied Charles Lyell’s Principles of Geology, which
described how Earth’s features developed slowly over long
periods by geologic processes (plate tectonics)
• He noted that many varieties of plants and animals could be
developed in just a few generations by artificial selection
Artificial Selection in Brassica oleracea
• Example: all members of
the same species, Brassica
oleracea
Figure 18.3: Artificial selection in
Brassica oleracea.
• An enlarged terminal bud (the “head”)
was selected in cabbage (lower left),
flower clusters in broccoli (upper left)
and cauliflower (middle right), axillary
buds in brussels sprouts (bottom
middle), leaves in collards (upper
right) and kale (lower right), and stems
in kohlrabi (middle).
Fig. 18-3, p. 394
Developing a Theory (cont.)
• Darwin studied an essay by Thomas Malthus (1766–1834)
which suggested that inherited variations favorable to survival
tend to be preserved, while unfavorable ones are eliminated
because of a struggle for resources.
• The result is adaptation, an evolutionary modification that
improves the chances of survival and reproductive success in
a given environment
• Eventually, the accumulation of modifications might result in a
new species
Darwin’s Theory of Natural Selection
• Darwin called his explanation for evolution natural selection,
in which better adapted organisms are more likely to survive
and become the parents of the next generation
• As a result of natural selection, the population changes over
successive generations; the frequency of favorable traits
increases, and less favorable traits become scarce
Darwin and Wallace
• Alfred Russel Wallace (1823–1913), a British naturalist who
studied plants and animals of the Malay Archipelago, arrived
at the same conclusion at the same time as Darwin
• Darwin’s book, On the Origin of Species by Natural Selection,
was published in 1859
• Wallace’s book, Contributions to the Theory of Natural
Selection, was published in 1870
Four Principles of Natural Selection
• Darwin’s mechanism of evolution by natural selection consists
of four observations on the natural world:
• Variation: Individuals in a population exhibit variation in
traits; some improve an individual’s chances of survival
and reproductive success – others do not
• Overproduction: In every generation each species has
the capacity to produce more offspring than can survive
• Limits on population growth: Organisms compete for
limited resources; not all survive to reproduce
• Differential reproductive success: Individuals with the
most favorable combination of characteristics are more
likely to survive and reproduce
Genetic variation in emerald tree boas
Island Populations
• Over time, enough changes may accumulate in
geographically separated populations (often with slightly
different environments) to produce new species
• Darwin noted that the 14 species of Galápagos finches may
have evolved in this way
• The different islands of the Galápagos kept the finches
isolated from one another, allowing them to diverge into
separate species in response to varying conditions
The Modern Synthesis
• Darwin was unable to explain how individuals transmit traits to
the next generation, or why individuals vary
• About the same time, Gregor Mendel was working on the
basic patterns of inheritance
• It was not until the 1930s and 1940s that biologists combined
the principles of Mendelian inheritance with Darwin’s theory of
natural selection to produce the modern synthesis
The Modern Synthesis (cont.)
• The modern synthesis explains Darwin’s observation of
variation among offspring in terms of mutation, or changes in
DNA, such as nucleotide substitutions
• The modern synthesis incorporates our expanding knowledge
in genetics, systematics, paleontology, developmental
biology, behavior, and ecology
The Effect of Chance on Evolution
• Natural selection appears to be a more important agent of
evolutionary change than chance
• Examples:
• Fruit fly evolution proceeded the same way on two
different continents (large and small wings)
Wing Size in Female Fruit Flies
• The evolutionary
pattern found in
Europe also
emerged in North
America after
accidental
introduction of D.
subobscura to the
Americas
Fig. 18-6, p. 397
KEY CONCEPTS 18.3
• Darwin’s scientific theory of evolution – natural selection –
explained how environmental forces could cause evolution
• Natural selection occurs because individuals with traits that
make them better adapted to local conditions are more likely
to survive and produce offspring than are individuals that are
not as well adapted
• Modern synthesis combines Darwin’s theory with genetics