Transcript Chapter 2 the Development of Evolutionary Theory

CHAPTER 2
The Development of Evolutionary Theory
Chapter Outline
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Brief History of Evolutionary Thought
Natural Selection
Natural Selection in Action
Constraints on Nineteenth-Century Evolutionary
Theory
Opposition to Evolution
Why It Matters
Focus Questions
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What are the basic premises of natural selection?
What were the technological and philosophical
changes that led people to accept notions of
evolutionary change?
Introduction to the Subject of Evolution
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Evolution is the most fundamental of all biological
processes, but one of the most misunderstood.
Humans evolved from a species that lived some 68 million years ago (mya), not monkeys or
chimpanzees.
Humans do share a recent common ancestor with
other primates
Evolution takes time; hence, the
appearance of a new species is rarely
witnessed (microevolutionary changes
occur, however: see Chapt. 1)
 The subject of evolution is controversial,
especially in the U.S. because of
conflicting spiritual teachings
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Evolution Is a Theory
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The theory has been tested and subjected to
verification through accumulated evidence (and has
not been disproved)
The theory of evolution has been supported by a
mounting body of genetic evidence.
The theory has stood the test of time.
The theory continues to grow.
A Brief History of Evolutionary Thought
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Evolutionary principles were developed in western
Europe, made possible by scientific thinking dating to
the 16th century.
Western science, however, borrowed ideas from Arab,
Indian, and Chinese cultures where notions of
biological evolution had already developed.
By the 19th century, evolution wasn’t a new concept,
but Natural Selection was a new theory
Natural Selection
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The most critical mechanism of evolutionary change,
first explained by Charles Darwin
Same conclusions were independently reached by
Alfred Russel Wallace.
Barrier to Evolutionary Thought: Fixity
of Species
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The notion that species,
once created, can never
change
an idea diametrically
opposed to theories of
biological evolution.
To challenge the idea was
to challenge the Argument
from Design (life
engineered by a
purposeful God).
The Scientific Revolution
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Came with the discovery of the New World,
introducing new ideas and challenging fundamental
views about the planet.
Exposure to new plants and animals increased
awareness of biological diversity.
Challenges to traditional beliefs
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Aristotle taught that the sun and planets existed in
a series of concentric spheres that revolved around
the sun.
Copernicus challenged the idea that the earth was
the center of the universe.
Galileo’s work supported the idea that the universe
was a place of motion.
Aristotle’s View
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This seventeenth-century
map shows the earth at the
center of the solar system.
Ideas generated out of the
Scientific Revolution
Challenges such longstanding beliefs
Precursors to the Theory of Evolution
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John Ray, a minister educated at Cambridge
University, developed the concept of species.
He recognized that groups of plants and animals
could be differentiated from other groups by their
ability to mate with one another and produce
offspring.
He placed such groups of reproductively isolated
organisms into a single category, which he called the
species.
Precursors to the Theory of Evolution
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Carolus Linnaeus, a Swedish naturalist who
developed a method of classifying plants and
animals.
In Systema Naturae, first published in 1735, he
standardized Ray’s use of genus and species
terminology and established the system of binomial
nomenclature.
He added two more categories: class and order.
Linnaeus’ four-level system became the basis for
taxonomy.
Precursors to the Theory of Evolution
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Erasmus Darwin, Charles Darwin’s grandfather
Physician, poet, and leading member of an
intellectual community in England
In a poem, expressed the view that life had
originated in the seas and all species descended from
a common ancestor.
Charles read his grandfather’s writings, but how much
he was influenced by them is unknown.
Precursors to the Theory of Evolution
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Jean-Baptiste Lamarck developed a theory to
explain the evolutionary process, known as the
inheritance of acquired characteristics.
An example is the giraffe: having stripped the
leaves from the lower branches of a tree, the
animal tries to reach leaves on upper branches.
The neck becomes slightly longer.
The longer neck is passed on to offspring.
Lamarck’s View of Evolution
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Individual changes, transmits that change to
offspring
Darwin-Wallace View of Evolution
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Environment favors individuals with long necks
Those individuals more likely than others to have
offspring
Georges Cuvier and Catastrophism
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An opponent to Lamarck,
Cuvier explained the fossil
record as the result of a
succession of catastrophes
followed by new creation
events.
The view that the earth’s
geological landscape is the
result of violent cataclysmic
events.
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Thomas Malthus, author of an essay that inspired
both Charles Darwin and Alfred Wallace in their
separate discoveries of natural selection.
Was arguing for limits of human population
growth, not concerned with how species change.
The limits for populations to increase is controlled
by availability of resources.
The latter was extended to all organisms by
Darwin and Wallace.
Charlies Lyell
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A lawyer, geologist, and, for Charles Darwin’s
friend and mentor.
Before meeting Darwin in 1836, Lyell had
earned acceptance in Europe’s most prestigious
scientific circles, thanks to his praised Principles
of Geology, published during the years 1830–
1833.
Uniformitarianism
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The theory that the earth’s features are the result of
long-term natural processes (i.e. wind, water erosion,
local flooding, frost, decomposition, volcanoes,
earthquakes, and glacial movements) that continue to
operate in the present as they did in the past.
Proposed by James Hutton, elaborated on by Lyell,
this theory opposed catastrophism and contributed
strongly to the concept of immense geological time.
These limestone cliffs in southern France were formed
around 300 million years ago from shells and the
skeletal remains of countless sea creatures.
Mary Anning
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When her father died, Anning began collecting
and selling marine fossils to support her family.
She discovered the first fossilized Pleiosaurus
(ocean-dwelling reptile) and became known as
one of the world’s leading “fossilists.”
Charles Darwin (1809-1882)
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Ideas were formed while
serving as a naturalist on
the 5-year voyage of the
HMS Beagle.
Darwin saw the importance
of biological variation within
a species.
Recognized that sexual
reproduction increased
variation, but did not yet
know why.
The Route of the HMS Beagle
The Struggle for Existence
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The idea that in each generation more offspring
are born than survive to adulthood, coupled with
the notions of competition for resources and
biological diversity led to the theory of evolution.
He wrote,“ It at once struck me that under these
circumstances favourable variations would tend to be
preserved, and unfavourable ones to be destroyed.”
Beak Variation in Darwin’s
Galápagos Finches
Ground finch
 Main food: seeds
 Beak: heavy
Beak Variation in Darwin’s
Galápagos Finches
Tree finch
 Main food: leaves, buds,
blossoms, fruits
 Beak: thick, short
Beak Variation in Darwin’s
Galápagos Finches
Tree finch (called
woodpecker finch)
 Main food: insects
 Beak: stout, straight
Beak Variation in Darwin’s
Galápagos Finches
Ground finch (known as
warbler finch)
 Main food: insects
 Beak: slender
Domestic Dogs
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All domestic dogs share a common ancestor, the wolf.
The extreme variation exhibited by dog breeds
today has been achieved in a relatively short time
through artificial selection.
Alfred Russell Wallace
(1823-1913)
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Suggested species descended from other
species and new species were influenced by
environmental factors.
Presented joint paper, coauthored with
Darwin, on evolution and natural selection to
the Linnean Society of London
Processes of Natural Selection, are “the
key” to understanding evolution
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Once Darwin understood how selection occurs in
nature, he outlined the processes.
Natural Selection, the basic
processes
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All species are capable of producing offspring at a
faster rate than food supplies increase.
There is biological variation within all species.
Since in each generation, more individuals are
produced than can survive, and because of limited
resources, there is competition (not necessarily the
same thing as fighting, however) among individuals.
Processes of Natural Selection
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Individuals possessing favorable variations or
traits (i.e. speed, resistance to disease, protective
coloration) have an advantage over those who do
not. In other words, have greater fitness because
favorable traits increase the likelihood of survival
and reproduction.
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The environmental context determines whether or
not a trait is beneficial. Hence, favorable traits
become most advantageous are the results of a
natural process.
Traits are inherited and passed on to the next
generation. Individuals who produce more
offspring are said to have a greater reproductive
success, or fitness.
Processes of Natural Selection
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Variations accumulate over long periods of time,
so later generations may be distinct from
ancestral ones.
As populations respond to pressures over time,
they may become distinct species, descended from
a common ancestor.
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Over long periods of geological time, successful
variations accumulate in a population
Later generations may be distinct from ancestral
ones, or a new species can appear.
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Geographical isolation (distance, natural barriers
such as oceans) contributes to the formation of new
species as individuals begin to adapt to different
environments.
Selective pressures (differential ecological
circumstances) cause distinct species to develop.
See, for example, the 13 species of Galápagos
finches presumably all descended from a common
South American ancestor.
Evolutionary Change
Through Natural Selection
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A trait must be inherited if natural selection is to act
on it.
Natural selection can’t occur without population
variation in inherited characteristics.
Fitness is a relative measure that changes as the
environment changes.
Natural selection can only act on traits that affect
reproduction.
Fitness
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Pertaining to natural selection, a measure of
relative reproductive success of individuals.
Fitness can be measured by an individual’s genetic
contribution to the next generation compared to
that of other individuals.
Fertility
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The ability to conceive and produce healthy
offspring.
An animal that gives birth to more young passes its
genes on a faster rate than one that bears few
offspring.
An important element, however, is also the number
of young raised successfully to the point where they
reproduce, or differential net reproductive success.
Genome
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With the discovery of the structure of DNA came
the understanding of the entire genetic makeup of
an individual or species.
Human and chimpanzee genomes were sequenced
in 2003 and 2005, respectively.
Biological Continuity
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Refers to a biological continuum.
When expressions of a phenomenon continuously
grade into one another so that there are no discrete
categories, they exist on a continuum.
Color is one such phenomenon, and life-forms are
another.
Most people hold to belief systems that do not
emphasize this or offer scientific explanations.
Religion and Science
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Religion and science concern different aspects of the
human experience, and they are not inherently
mutually exclusive categories.
Belief in God does not exclude the possibility of
biological evolution; acknowledgement of
evolutionary processes doesn’t preclude the existence
of God.
Evolutionary theories are not rejected by all religions
or by most forms of Christianity.
Scopes Monkey Trial
Clarence Darrow sitting on the edge of the table; John Scopes sitting
with arms folded behind Darrow
Christian Fundamentalists
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Conservative Christians (“Creationists”) seeking a
revival of “traditional values” and banning any theory
that does not support the biblical version of the
creation of humankind.
Adherents to a movement in American Protestantism
that began in the early twentieth century.
This group holds that the teachings of the Bible are
infallible and are to be taken literally.
Creation Science, Intelligent Design
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Argue that creation science and intelligent design (ID)
is as much a scientific endeavor as is evolution, and
suggest scientific evidence to support creationist views
ID is not science, however
Creationists argue their view is absolute and fallible,
which is counter to science which seeks testable
hypotheses
Why It Matters
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One of the greatest controversies regarding
education in the United States and other parts of
the world is the teaching of evolution.
Example: HINI Flu viruses are the result of viruses
“evolving” or changing in form.
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Medical researchers try to predict which of several
strains will pose the most serious threat and try to
develop a vaccine that targets that specific “evolving”
strain.
If future physicians and researchers don’t understand
evolution, there is little hope they can forestall
potential medical crises as the pace of change in
pathogens exceeds that of the antibiotics designed to
defeat them.
Contemporary Health Challenges
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The inevitable outcome of our more aggressive
methods to fight microbes (disease causing microorganisms such as bacteria and viruses) will lead to
modified micro-organisms that have evolved to resist
therapies such as antibiotics. More use of antibiotics
to treat bacterial infections weed out vulnerable
microbes, but leave less vulnerable to reproduce. Less
vulnerable cause more serious forms of disease than
the organisms that were eliminated.
QUICK QUIZ
1. To understand the complexities of evolution one
must be well versed in
a)
b)
c)
d)
mathematics and statistics.
botany and paleontology.
genetics and biology.
anatomy and physiology.
Answer: c
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To understand the complexities of evolution one
must be well versed in genetics and biology.
2. Genetic evidence supports evolution.
a)
b)
True
False
Answer: true
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Genetic evidence supports evolution
3. Darwin realized that variation among
_________________ was how selection occurred,
ultimately causing change in species.
Answer: individuals
• Darwin realized that variation among individuals
was how selection occurred, ultimately causing
change in species
5. Natural selection acts on existing
_________________ within a species.
Answer: variation
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Natural selection acts on existing variation within a
species.