Transcript Mass extinction

Evolution and Biodiversity
G. Tyler Miller’s
Living in the Environment
14th Edition
Chapter 5
Chapter 5: Essential Questions / Objectives
Briefly describe the evolution of life from chemical evolution to
the development of eukaryotic cells.
Briefly describe the theory of evolution, being sure to include
the roles played by variation within the gene pool and natural
selection, extinction, speciation, and adaptive radiation.
Describe the tools available to researchers for learning the
evolutionary history of life. (evidence for evolution)
Define natural selection and the three conditions that are
necessary for evolution of a population by natural selection.
Summarize and address two common misconceptions
about evolution.
Define coevolution.
Distinguish between a specialist and a generalist. Evaluate
the conditions that favor these two approaches.
Define ecological niche. Distinguish between condition and
resource; fundamental niche and realized niche. List the
factors that determine the realized niche.
Define speciation and compare allopatric speciation with
sympatric speciation. Indicate which of these mechanisms
is more common.
Define extinction and distinguish between background
extinction and mass extinction. Discuss the role of humans
on the rate of extinction at present.
Discuss the pros and cons of artificial selection and genetic
engineering. Consider the possible environmental impacts
on resource use, pollution, and environmental degradation.
Indicate what it is that has allowed humans to have such a
profound influence
Origins and Early Evolution of Life
Chemical evolution of organic molecules, biopolymers, and systems of
chemical reactions were needed to form the first cell. It took about 1
billion years.
Biological evolution followed, from single-celled prokaryotic bacteria to
single-celled eukaryotic organisms to multicellular organisms. Is has
been continuing for 3.7 billion years.
Knowledge of past life comes from fossils, ice-core drilling, chemical
analysis, and DNA analysis. These records are incomplete
The Theory of Evolution - Widely accepted scientific idea that
all life forms developed from earlier life forms. Although this
theory conflicts with the creation stories of many religions, it is
the way biologists explain how life has changed over the past
3.6 - 3.8 billion years and why it is so diverse today.
The Five Parts of Darwin’s Theory of Evolution
Perpetual Change
Common Descent
Multiplication of Species
Gradualism
Natural Selection
Galapagos Islands satellite view.
Darwin’s Observations and Inferences:
Observation 1 – Organism have great potential fertility
Observation 2 – Natural populations normally remain
constant in size except for minor fluctuations
Observation 3 – Natural resources are limited
Inference 1 – There exists a continuing struggle for
existence among members of a population
Observation 4 – All organisms show variation
Observation 5 – Some variation is heritable
Inference 2 – There is differential survival and
reproduction among varying organisms in a
population
What Drives Evolution ?
Variation
Meiotic mix
Population Dynamics
Mutations
Struggle for Existence
Competition
Predation
Selective advantage
Natural Selection
Process by which a particular beneficial gene (or set of genes) is
reproduced in succeeding generations more than other genes. The
result of natural selection is a population that contains a greater
proportion of organisms better adapted to certain environmental
conditions. Conditions for Natural Selection Included:
1. There is genetic variation within the population
2. Traits must heritable – past from one generation to the next
3. The adaptation allows the organism to better survive under prevailing
environmental conditions.
Differential reproduction - Phenomenon in which individuals with adaptive
genetic traits produce more living offspring than do individuals without
such traits.
Differential Reproduction
Misconceptions about Evolution
Evolution is the change in a population's genetic makeup over time.
Therefore, population evolve not individuals
Evolution is concerned with leaving the most descendants, NOT the
strongest ones.
There is no master plan to achieve genetic perfection.
Evolution and Adaptation
Macroevolution: long term , large scale evolutionary changes through
which new species form from ancestral species and other species
are lost through extinction. “speciation”
Microevolution: small genetic changes that occur in a population.
“variation within a species”
Genes mutate
Individuals are selected
Populations evolve
Gene pool: a collection of genes potentially available to members’
offspring in the next generation “ genetic variability in a population”
Sexual reproduction leads to random recombination of alleles from
individual to individual.
Coevolution: Interacting species can engage in a back-and-forth genetic
contest in which each gains a temporary genetic advantage over the
other.
Evolutionary Arms Race
Mutation: random changes structure or number of DNA molecules in a
cell that can be inherited by offspring.
Mutations occur in two ways:
Gene DNA is exposed to external agents like X rays, chemicals
(mutagens), or radioactivity
Random mistakes that occur in coded genetic instructions
Only mutations in reproductive cells are passed to offspring.
Many mutations are neutral; some are deadly; and a few are
beneficial.
Fruit fly (Drosophila) adult, dorsal
view
Fruit fly (Drosophila melangoaster)
Vestigial Wing.
Types Selection
Stabilizing
Directional – demonstrated by the
peppered moths
Stabilizing – tends to favor the
average
Disruptive – may lead to speciation
Disruptive
What Limits Adaptation?
A population's gene pool and its rate of reproduction limit
the population's ability to adapt to new environmental
conditions.
The only genetic traits that can adapt are those already in
the gene pool.
A population's reproductive capacity limits those genes that
can adapt.
Genetically diverse species that reproduce quickly can often
adapt quickly.
Populations that reproduce slowly take a long time to adapt
through natural selection.
For a new favorable trait to predominate, most of an existing
population would have to die prematurely.
The Fossil Record as
Evidence for Evolution
Fossils Skeletons, bones, shells,
body parts, leaves, seeds, or
impressions of such items that
provide recognizable evidence of
organisms that lived long ago.
Fossil of algae, Gunflint chert, 2.1 billion years old.
Brightfield X400.
Burgess Shale arthropod fossils, 530 years old,
Middle Cambrian Period.
Trilobite fossil from the Silurian period 405mya.
Comparative anatomy
Darwin recognized the major source of
evidence for common descent was
found in the concept of homology.
Homology is the name given to
similarity of organs or structures due to
common embryonic or evolutionary
origin.
Forelimbs of five vertebrates show
skeletal homologies:
Yellow --- Humerus
Blue ---- radius and ulna
Pink ---- wrist
White ---- phalanges
Clear homologies of bones and
patterns of connection are evident
despite evolutionary modifications for
particular functions
Phylogenetic
Reconstruction
The phylogenetic pattern
specified by 15 homologous
structures in the skeletons
of ratite (flightless) birds.
The homologous features
are numbered 1-15 and are
marked both on the
branches of the tree on
which they arose and on
the birds that them
Simplified phylogenetic
reconstruction of
vertebrates
Transitional Species
Whale evolution - the
movement of the nostrils
from the front of the
skull to the top of the
skull
Why is having the
nostrils at the top of the
skull an advantage?
Environmental changes require
adaptations also. Organisms must be
able to adapt to the new conditions,
migrate to an area with a more
favorable environment, or become
extinct.
DNA Evidence for Evolution
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_04.html
Ice cores unlock climate
secrets
Gases and particles trapped in the layers
of an ice core provide information about
the Earth's climate and atmosphere.
Oxygen and hydrogen isotopes reveal the
temperature when the ice formed, for
example, while high carbon dioxide and
methane levels indicate periods of global
warming.
Geological Time and Major
Evolutionary Events
Age of
reptiles
Insects and
amphibians
invade the land
Age of
mammals
Photosynthesis
and Oxygen
Recorded human
history begins
1/4 second
before midnight
Origins of the
Eukaryotic Cells
midnight
Origin of life
(3.6–3.8 billion
years ago)
The Cambrian
Explosion
Movement on to
land
First fossil
record of
animals
Plants
begin
invading
land
Modern humans
(Homo sapiens)
appear about
2 seconds
before midnight
noon
Evolution and
expansion of life
Ecological Niches and Adaptation
An ecological niche is a species' way of life in an ecosystem, everything
that affects its survival and reproduction.
The niche includes the member's adaptations, its range of tolerance for
physical and chemical conditions, its interactions with other
components of the ecosystem, and its role in energy flow and matter
recycling.
This is NOT the same as the organism's habitat.
The habitat is the physical location where a species lives.
The fundamental niche is the full potential range of conditions and
resources a species could use.
Its realized niche is the part of the potential niche that allows a species to
survive and avoid competition with other species for the same
resources
Ecological Niches and Adaptation
Fig. 5-4 p. 91
Broad and Narrow Niches
Generalists
Specialists
Some species have broad
ecological roles and are termed
generalist species.
Some species have narrow
ecological roles and are termed
specialist species.
Their living range is broad and
includes many different places.
Specialist species can live only in
very specific environments.
They can eat a variety of foods and
tolerate a wide range of
environments.
This makes them more prone to
extinction when environmental
conditions change.
If the environment is changeable,
the generalist will survive better
than the specialist.
If the environment is constant,
specialists have fewer
competitors.
Intense competition may lead to
evolutionary divergence of a
single species into a variety of
similar species with specialized
niches.
Speciation: A new species arises when members of a
population are isolated from other members so long that
changes in their genetic makeup prevent them from producing
fertile offspring if they get together again.
Fig. 5-7 p. 94
Speciation
Natural selection can lead to development of an entirely new species.
In speciation, two species arise from one when some members of a
population cannot breed with other members to produce fertile
offspring.
Allopatric Speciation is the most common mechanism and occurs in two
phases:
Geographic isolation: physical separation for long time periods
Reproductive isolation: the gene pools are so changed that members
become so different in
genetic makeup that they cannot produce fertile offspring
Allopatric Speciation
Exactly how speciation occurs is not
well understood. Most biologists
believe in Allopatric (“other
place”) Speciation: A small
population becomes
geographically isolated in some
way.
Breeding only among
themselves, its members evolve
away from the ancestral
Humans and chimpanzees
diverged, it is believe, because
the ancestral species was
divided by Africa’s Great Rift
Valley
Sympatric Speciation
Sympatric Speciation is less
common. It occurs when
two species live close
together but can't
interbreed due to a
mutation or subtle changes
in behavior.
Northern Fence Lizard (Sceloporus undulatus
hyacinthinus) male and female, showing sexual
dimorphism.
Sympatric speciation can involve
seasonal or habitat isolationpotential mates aren’t in the same
place at the same time- or
behavioral isolation, for example
when a courtship ritual develops
that appeals to some but not all.
Extinction
When population members cannot adapt to changing environmental
conditions, the species becomes
extinct.
A species manages to survive one to ten million years before extinction
occurs.
Life has had to cope with many major natural disasters that may reduce or
eliminate species.
Introduction of new species into an area has also led to reduction in number
or elimination of species.
When local environmental conditions change, some species will disappear
at a low rate; this is called background extinction.
Mass extinction is a significant rise in extinction rates above the background
extinction level. Usually, from 25-70% of species are lost. Recent
evidence suggests that there have been two mass extinctions on
Earth. There appear to have been three mass depletions on Earth.
Mass depletions are periods of extinction are higher than normal , but not
high enough to classify as a mass extinction
Mass Extinction
Terrestrial
organisms
Cretaceous
400
Quaternary
Marine
organisms
Tertiary
Jurassic
Triassic
Permian
Devonian
Silurian
Carboniferous
800
Ordovician
1200
Cambrian
Number of families
1600
Pre-cambrain
Adaptive radiations are recovery
periods after mass extinction
when numerous new species
evolve to fill niches in changed
environments. It takes one to ten
million years to rebuild biological
diversity after a mass
extinction/depletion.
0
3500 545
500
440 410
355
290
250
Millions of years ago
205
145
65
1.8 0
Continental drift plays a role in speciation and extinction by isolating
populations both geographically and reproductively
LAURASIA
120° 80°
40°
80°
120°
120° 80°
80°
120°
GONDWANALAND
135 million years ago
225 million years ago
EURASIA
AFRICA
120° 80°
120°
120°
0°
MADAGASCAR
65 million years ago
Present
40°
120°
Evolutionary tree models
Evolutionary tree diagrams interaction.
Click to view
animation.
Human Impact on Extinction
The Earth's biodiversity is decreasing because of human activities.
Biodiversity equals speciation minus extinction.
Humans are causing the premature extinction of species, estimated to
be 100 to 1,000 species per million species.
It has been predicted that by the end of the 21st century we may see
the extinction of half of the present species now on Earth.
Humans and their activities are also destroying/degrading ecosystems
that might be centers for future speciation.
Human Impacts on Evolution
 Artificial Selection
Genetic Engineering
Concerns about Genetic Engineering
What is the Future of Evolution?
Man has used artificial selection to change the
genetic characteristics of populations.
We use selective breeding to obtain specific
desired traits.
Traditional crossbreeding is a slow process; it
takes many generations of selection for the
desired trait.
Wild and cultivated roses illustrating artificial selection.
What is the Future of Evolution?
Genetic engineering/gene splicing are techniques that isolate, modify,
multiply, and recombine genes from different organisms. Genes from
different species that would never interbreed in nature are being
transferred to each other.
Genetically modified organisms (GMOs)/transgenic organisms are the
results of this gene splicing.
Gene splicing takes half as much time to develop a new crop/animal,
as does traditional crossbreeding.
Cloning produces a genetically identical version of an individual.
Biopharming is a new field where genetically engineered animals act
as biofactories to produce drugs, vaccines, antibodies, hormones,
etc.
Phase 2
Make Transgenic Cell
Phase 1
Make Modified Gene
cell
Identify and extract
gene with desired trait
Identify and remove
portion of DNA
with desired trait
Transfer plasmid
copies to a carrier
agrobacterium
gene
A. tumefaciens
(agrobacterium)
DNA
Agrobacterium
inserts foreign
DNA into plant
cell to yield
transgenic cell
plasmid
Remove plasmid
from DNA of E. coli
Genetically
modified
plasmid
plasmid
Host DNA
Foreign DNA
Transfer plasmid
to surface
microscopic metal
particle
Insert modified
plasmid into E. coli
Grow in tissue
culture to
make copies
Nucleus
E. coli
DNA
Insert extracted DNA
(step 2) into plasmid
(step3)
Plant cell
Use gene gun
to inject DNA
into plant cell
Phase 3
Grow Genetically Engineered Plant
Transgenic cell
from Phase 2
Cell division of
transgenic cells
Genetic engineering is an
unpredictable process and
raises privacy, ethical,
legal, and environmental
issues. It is a trial and error
process.
The average success rate of
genetic engineering
experiments is about 1%.
There are many questions
about gene therapy:
Culture cells
to form plantlets
Transfer to soil
Transgenic plants
with new traits
Who will be helped with genetic
knowledge — only those who
can pay for it?
If one has a defect, will he or she
be able to get health
insurance, or a job?
Should we clone spare parts for
people's bodies?
Genetic Engineering
A backlash developed in the 1990s against increased use of genetically modified
food plants and animals.
Proponents of more careful control of genetic engineering point out that most new
technologies have had unintended, harmful consequences, so caution
should be practiced regarding genetic
engineering.
What is the Future of Evolution?
Humans have become such a powerful species so quickly due to two
evolutionary adaptations: a complex brain and strong opposable
thumbs.
Humans have quickly developed powerful technologies to meet our needs
and wants.
Humans need to change our ways in order not to be called Homo
ignoramus instead of Homo sapiens sapiens, the doubly wise.
Resources:
http://www.pbs.org/wgbh/evolution/