Transcript Evolution: Descent with Modifications

Evolution: Descent with Modifications
Evolution is a process….
that has transformed life on Earth from its
earliest forms to the diversity seen today
Historical context:
• Classic Greek philosophers
• Biblical ideas
• Linnaeus develops taxonomy to organize life, gives
us the system of binomial nomenclature.
• Cuvier studies fossils and advocates catastrophism.
• Hutton saw gradualism as cause for Earth’s changes
• Lyell described uniformitarianism stating geological
processes are the same today as in the past.
A Role For Fossils
• Lamarck, a French biologist at a Natural History
Museum, compared fossils to living species.
• He developed two concepts:
• Use/ disuse theory….Body parts used extensively
become larger and stronger; those parts not used
decrease is size.
• Organisms could pass acquired physical changes
onto their offspring.
• Lamarck is remembered for his explanation of
the giraffe
***BEWARE OF USING GIRAFFE EXAMPLES IN
ESSAYS on evolution!
• Although Lamarck was wrong he did attempt
to use the fossil record to explain Earth’s
diversity of life. Lamarck also recognized this
required gradual, evolutionary change over
very long periods of time.
Charles Darwin (1809-1882)
• Interested in nature from an
early age.
• Graduated from Christ College
at Cambridge in 1831.
• Recommended by his professor
to serve as naturalist for HMS
Beagle.
• The Beagle was to sail around
the world over the next 5 yrs.
Development of Darwin’s theories:
• As Naturalist, Darwin was given the freedom
to explore exotic and diverse species of plants
and animals on South American coastlines.
• Darwin noted species were vastly different in
South America than in Europe, even thought
the habitats were similar.
• Even the fossil record indicated species
diversity.
• While in Chili Darwin experienced an earthquake that
significantly elevated the coastline. Darwin saw a
mechanism to explain the presence of ocean fossils
high in the Andes mountains.
The volcanic Galapagos Islands 900 km off the
coast of South America led Darwin to
hypothesize the original island inhabitants came
from the mainland.
Darwin began to understand that a relationship
existed between the origin of new species and
the adaptations of species to their environments
on different islands.
Darwin’s
Finches…..
• Darwin noted there
were differences in 13
varieties of finches in
the Galapagos. The
finches had
developed special
adaptations for eating
varieties of foods on
their home island.
Alfred Wallace, naturalist from East Indies, was developing
ideas about natural selection and sent his manuscript to
Darwin in 1858.
Darwin rushed to complete and published his book ,
The Origin of Species ,in which came out in 1859.
Darwin is credited with
the theory of evolution by
natural selection. He
accumulated great support
for his ideas and presented
strong logical arguments
for his conclusions. His 15
yr old notebooks prove
Darwin had the idea first.
DARWIN’S MAIN IDEAS
1) Descent with modification….
Organisms share a common ancestry
in their remote past.
2) Descendents of the common ancestor have
accumulated diverse adaptations to allow
them to survive and reproduce in their
various habitats.
3) Natural selection is the mechanism of
adaptive evolution.
Natural Selection :
The Basic Observations
1)
2)
3)
4)
Species have the potential to produce large
numbers of offspring.
Environmental resources are limited.
These conditions lead to a struggle for
existence among individuals within a
population.
Individuals within a population exhibit genetic
differences . Those whose traits are best suited
for their environment are likely to leave more
offspring.
Sources of Genetic Differences?
Mutations-change in the DNA that can alter the
gene and the individual’s phenotype
Sexual Reproduction- crossing over, independent
assortment and gamete selection.
Polymorphisms – 2 or more phenotypes exist for a
given trait
IMPORTANT FACTS :
• Evolution acts on populations NOT on individuals.
• Natural Selection can only works on traits that can
be passed from generation to generation.
• Natural selection IS A PROCESS used to bring about
evolution.
• Adaptations are a result of natural selection and
include physical traits, behaviors, lifespan, etc.
What evidence supports evolution?
• Homologous Structures
• Fossil Record
• Vestigial Structures
• Molecular Evidence
Population Genetics
• Evolutionary
concepts were
better accepted
once scientists
understood the
importance of
genetic
differences within
populations.
So what else contributes to evolution?
• Mutations- DNA changes alter allele frequency
• Gene flow- Change in frequency of alleles in a
population as genes move between populations.
• Nonrandom mating – Selective breeding
• Genetic drift- Changes in allele frequencies
because of a random, chance event in a small
population.
• Selection –Organisms have genetic traits in
greater proportions in a population than others
Mutations:
• Mutations rates are rare
for a given gene.
• The cumulative effect of
ALL mutations in the
genome of an individual
can be significant .
• Mutations serve as the
source of genetic
variation , thus the raw
material for natural
selection in populations.
Gene Flow
• Populations gain or lose
genes with the movement
of individuals within a
population.
• Gene flow tends to
REDUCE the differences
between populations.
Genetic Drift
A change in the
gene pool of small
populations due to
chance. Several
mechanisms can
cause this :
1) Bottleneck
Effect
2) Founders Effect
The Bottleneck Effect
• Even without movement, populations can be
drastically reduced in size
• Flooding, drought, epidemic disease, other
natural forces or progressive changes in the
environment are all causes
• the few survivors represent a random genetic
sample of the original population
• the resultant loss of genetic variability has
been termed the bottleneck effect
The Bottleneck Effect
Founder Effects
• Sometimes one or a few individuals disperse
and become the founders of a new, isolated
population at some distance from their place
of origin
• Since these individuals may not represent all
of the alleles present in the original
population, alleles are lost and frequencies of
alleles changed. Examples include:
• Darwin’s finches
• the blue people of Kentucky
Selection
Adaptations
involving genetic
changes that
result in an
increased
opportunity for
some organisms
to leave behind
more progeny
than other
organisms.
Types of Selection
• Natural selection— nature decides! The
environmental conditions determine which
individuals in a population produce the most
offspring
• Artificial selection— a breeder decides! The
breeder makes purposeful crosses between
animals or plants to produce a set of desired
characteristics
Nonrandom Mating
& Artificial selection!
Breeding with
individuals
selected for
specific
characteristics or
close proximity
alters the
frequencies of the
various genotypes
and increases the
chances for
homozygous
individuals.
Selection to Avoid Predators
• Camouflage—green caterpillars blend into the leaves
upon which they feed making it more difficult for
birds to see them.
• The peppered moth vs. the environment:
The trees in England are covered in light bark and
lichens. During the industrial revolution, soot
covered the trees making them dark. There was a
complete swap between the frequencies of light,
peppered moths and their dark, near black, cousins.
Birds are quite adept at picking out individuals that
are not adapted to their backgrounds.
The Peppered Moth
• Before 1850 the trees were
light and although black
coloration is dominant, it
was rare
• After the industrial
revolution that situation
reversed
• Disruptive Selection—intermediate types are
eliminated
• African fire-bellied seedcracker finch
– Populations of these birds contain
individuals with large and small beaks while
very few individuals have intermediatesized beaks.
– Why? The seeds they feed upon come in
two sizes, small and large
– Intermediate beaks are clumsy with small
seeds and not strong enough to crack large
seeds.
• Directional
selection—acts to
eliminate one
extreme from an
array of phenotypes
• Selection has
changed the
population in the
direction of lower
light attraction
toward light.
• Stabilizing
selection—selection
acts to eliminate
both extremes; it
favors an optimum
condition and
increases the
frequency of the
already common
intermediate type,
making it even more
common by
eliminating the
extremes.
Comparing Graphs Of Selection Types:
Evolution can lead to speciation
• Three processes can lead to the creation of
new species:
• Sympatric –Breeding is prevented even
though there is no physical barrier.
• Allopatric – Breeding is prevented due to a
physical barrier.
• Selective breeding – nonrandom breeding to
select for or against certain traits.
Reproductive Barriers
• Prezygotic Barriers are
mechanisms that
prevent the formation
of zygotes.
– Geographic Isolation
– Ecological Isolation
– Behavioral Isolation
– Temporal Isolation
– Mechanical Isolation
– No gamete fusion
• Postzygotic Isolation
– Hybrid embryos
do not correctly
develop
– Hybrid adults do
not survive
– Hybrid adults are
sterile or have
reduced fertility
Divergent Evolution
As species change over time the genetic
differences between them grows larger.
The longer their genetic lines have been
separate the more differences are visible
in their DNA and proteins.
Convergent
Evolution
The independent
development of
similar
structures in
organisms that
are not directly
related. This
often occurs in
organisms living
in similar
environments.
• The end result of all these mechanisms of
change is that populations will gradually move
toward having more individuals with
advantageous characteristics. This should
strengthen the population.
• As a population evolves it becomes better
adapted to its local environment.
Evolution Sample AP Test
questions
1. The different species of finches on the
Galapagos Islands are believed to have arisen
as a result of the natural selection acting on
populations that experienced
1.
2.
3.
4.
5.
Convergent evolution
Gene flow
Geographic isolation
Behavioral isolation
Hardy Weinberg Principles
2. The wing of a bat, the flipper of a whale and the
forelimb of a horse appear very different, yet
detailed studies reveal the presence of the same
basic bone pattern. These structures are examples
of
a)
b)
c)
d)
e)
Analogous structures
Homologous structures
Vestigial structures
Balanced polymorphism
Convergent evolution
HOMEWORK – A SHORT ESSAY:
Provide an example from molecular
evidence ( DNA sequencing), the fossil
record, homologous structures and
embryology to support the Modern
Theory of Evolution.
You have 5 and 7 minutes to write on
this question.
1992 Essay Question :
4. Evolution is one of the major unifying concepts
of modern biology.
a. Explain the mechanisms that lead to
evolutionary change.
b. Describe how scientists use each of the
following as evidence for evolution.
(1)
(2)
(3)
Bacterial resistance to antibiotics
Comparative biochemistry
The fossil record