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Evolution Lecture
Chapter 25
I.
Darwin 1831-1859
A. Voyage of the Beagle
B. Natural selection
C. Origin of Species
D. Gift to Biology
II.
Evolution of Populations - Microevolution
A. Background
B. Concept of Fitness
C. Mechanisms: Natural Selection and Genetic Variability
III.
Evolution of Species – Macroevolution
A. Concept of Species in Biology
B. Mechanisms of Evolution
IV.
Evolution in Action (see text)
A. Antibiotic Resistance
B. Genetically Modified Organisms (GMO’s)
C. Melanism in the Pepper moth (UK)
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I.
Darwin: 1831-1859
A.
“Voyage of the Beagle”
Darwin was 22 when he set off on the HMS Beagle as the
naturalist
Purpose of the Beagle’s voyage was to map the uncharted regions
of South America and Darwin was suppose to catalogue the
flora and fauna
Convention of the time relative to the natural sciences – static view
of all aspects of nature as if pre-ordained
Power of observation: highlight the significance of what Darwin
did: he observed and recorded information and
subsequently offered a mechanistic explanation for the
data…analogy to the lab exercises in course
B.
Notable observations by Darwin (remember Darwin’s frame of
reference…diversity of landscape in UK comparable to blandness of food
in UK)
South America
Diversity of landscapes
Brazilian rainforests
Grasslands/savannas of Argentina
Dry desserts of Tierra del Fuego (tip)
Towering landscapes of the Andes
Flora and fauna distinct from Europe and UK
Array of structures on flora and fauna that appeared to be
of value in the unique array of habitats –
adaptations
Seeding of idea: living systems are not static as
conventional wisdom but vary substantially as a
function of the environment
Galapagos (key event to the formulation of “Origin of
Species”)
Volcanic island off the coast of Ecuador and Peru…800
KM…recent origin…in eastern Pacific
Fauna on the island was not observed anywhere
else…unique
Most of fauna had distinct lineage to species on the S.
American mainland
e.g., 13 species of finches (bill structure)
Seeding of idea: fauna arrived on Galapagos from S.
American mainland and then diversified
C.
Natural Selection - Return to England
Two seminal ideas in 1836 leading to concept of the origin of
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species
1. Population growth far exceeds available resources or more
offspring are produced than can survive…common trait of
all organisms (Malthus)
2. Competition for resources (food, water, light, mates etc.)
limits number of offspring that can survive (e.g., maples
trees produce thousands of seed of which only a handful
ever germinate and grow into seedlings)
Environment could drive the origin of species via the gradual
accumulation of traits that steadily improve survivability over
time
D.
Natural Selection…1840
Developed concept that organisms differ in their success in
Reproduction and, by so doing, contribute differently to
future generations
Developed parallel concept that the driving force for this
differential success was natural selection that acts on the
variability among individuals
Product of this process is the developed of adaptations to enhance
success (relate back to observation in S. America while on
Beagle…the multitude of structures on the flora and fauna in each
type of habitat that appeared to be of value in surviving)
D. Origin of Species published in 1859
Two key tenets
1. Species arose/evolve gradually from ancestral species
2. Mechanisms is natural selection
E. Gift to Biology – theory of evolution
Diversity and similarity of all living organisms both result from the same
process
1. Evolution tends to preserve traits that confer an advantage
2. Evolution also adopts new traits that enhance survival and
reproductive success
Mechanism is natural selection
Origin of species is through the gradual accumulation of traits
More individuals are produced than can possibly survive, leading to a
fierce competition for resources
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Discuss what a theory is…an attempt to mechanistically explain a major
overarching pattern in sciences…one that is comprehensive
Newton and gravity
Bohr and the atom
Key is that theories are major unifying concepts in the sciences
II.
Evolution of Populations – Microevolution
A. Background
Misconception that individual evolves…individuals develop (explain
gene expression in develop)…populations evolve
Hierarchy of units in living systems
Ecosystems
Communities
Species
Populations
Individuals
Etc.
Just as ecosystems are key to understanding ecology and cells are
instrumental to organisms, populations are the fundamental unit
for understanding the process of evolution
Evolution at the level of populations is called microevolution and the
process involves a change in the genetic makeup of populations over
time
This concept is not embodied in Darwin’s Origin of Species because
Mendel’s work on inheritance in peas was not published until 1865 so
Darwin did not know how traits were inherited
B. Concept of Fitness
Fitness is the relative contribution of an individual to the gene pool of the
next generation
Contrast with:
“survival of the fittest”
“struggle for survival”
Key is the contribution to the next generation
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Example of sexual dimorphism in animal
males are commonly “ornate” with plumage and structure to attract
mates (e.g., birds)
same features are also attractive to predators so that individuals
with bright plumage probably do not live very long in
nature
however, these organisms are the most fit because they are the
ones who mate the most with female counterparts and
therefore contribute the most to the gene pool of future
generations
Mechanism: Natural Selection and Genetic Variability
The new synthesis essentially placed the two foundations of evolution at
parity;
 natural selection as presented by Darwin
 concept that individuals differ genetically in their fitness
The result being that the gene pool of the next generation will reflect the
action of natural selection on the inherited variation at the population level
III.
Evolution of Species – Macroevolution
Concept of species in Biology
Species is defined as the unit in the hierarchy that is reproductively
isolated from other units
Examples:
Maple species (10+) all exhibiting common characteristics of
maples but each species being incapable of breeding with
members of the other species
Humans and the evolution of the species
Mechanisms of Evolution at the species level
The mechanism is the same as presented by Darwin in that gradual
changes in the gene pool accumulate over time (generations), resulting in
lineages being isolated genetically and incapable of interbreeding
IV.
Evolution in Action – Some Case Studies (see text)
A. Antibiotic Resistance
100+ antibiotics used since 1940’s
Microbes and their generation times (hours) relative to humans (20 years)
Intense selection pressure (natural selection) for resistance to antibiotics has
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resulted in a variety of strains that evolved resistance and therefore
make the antibiotic less effective…
B.
Genetically Modified Organisms (GMO’s)
This is a special case of and one that is just emerging in national and
international prominence…it involves genetic alterations of the gene
pool (intentional to improve the utility of certain crops and
organisms) and as such the study of GMO’s is the domain of the
discipline of evolution. The key is trying to understand the
consequences of alterations in the gene pool.
C.
Melanism in Moths (see text for discussion)