Transcript Chapter 16 The Theory of Evolution

Chapter 16 The Theory of Evolution
What You’ll Learn
What did Charles
Darwin Contribute
to Science?
What are the Patterns
of biodiversity
Darwin noted?
Evolution: process of change through
time
The change in characteristics of
populations through generations. Thus,
existing life forms have evolved from
earlier life forms
 A unifying principle for biology.
 Provides an explanation for the
difference in structure, function, and
behavior among organisms

Fossils shape ideas about evolution
Fossils: direct or indirect remains of organisms
preserved in media such as sedimentary rock, amber,
ice, or tar
Ammonite casts
–Fossilized organic
matter in a leaf
Ice Man”
Fossils shape ideas about evolution

When geologists provided evidence
indicating that Earth was much older than
many people had originally thought,
biologists began to suspect that species
change over time, or evolve
A sea voyage helped Darwin frame his theory
of evolution
 The voyage of the Beagle 1831, ship’s
naturalist


Charles Darwin observed
 Species vary globally
○ Different, yet ecologically similar, animal species inhabited separated, but
ecologically similar habitats.
 Species vary Locally
○ Different, yet related, animal species often occupied different habitats
within a local area.
 Species vary over time
○ Some fossils of extinct animals were similar to living species
Ideas Influencing Darwin
Hutton and Lyell concluded that Earth is
extremely old and the processes that
changed Earth in the past are the same
processes of the present –
Uniformitarianism
 Lamarck suggested that organisms
could change by selectively using or not
using traits and passing those acquired
traits to their offspring. This caused
them to change over time.

Malthus
Reasoned that if the human population
grew unchecked, there wouldn’t be
enough living space and food for
everyone.
 Darwin applied this idea to other
organisms.

Artificial Selection
Darwin studied changes produced by
plant and animal breeders.
 Some of these variations can be passed
from parents to offspring to improve
crops and livestock.
 Humans select the useful traits.

Evolutionary theory

Darwin became convinced that the Earth
was old and continually changing
 He concluded that living things also change,
or evolve over generations
 He also stated that living species descended
from earlier life-forms: descent with
modification
Darwin’s Ideas
The Struggle for existence
1.

If more individuals are produced than can
survive, a population must compete for food,
living space, and other resources.
Variation and Adaptation
2.

Some traits enable a species to survive better
than others. Those species survive and pass
those desirable traits to their offspring.
Survival of the Fittest
3.

The more fit and organism is for the
environment it lives in, the better it’s fitness or
survival
DARWIN’S THEORY AND THE MODERN
SYNTHESIS

Darwin also saw that humans choose
organisms with specific characteristics
Breeding organisms with specific traits
in order to produce offspring with
identical traits is called artificial
selection.

Darwin hypothesized that there was a force
in nature that worked like artificial
selection.
Natural selection - the mechanism of
evolution


Darwin hypothesized that there was a force in nature
that worked like artificial selection.
Darwin concluded that individuals best suited for a
particular environment are more likely to survive and
reproduce than those less well adapted
 As a result, the proportion of individuals with favorable
characteristics increases
 Populations gradually change in response to the environment

Organisms without these variations are less likely to
survive and reproduce.
Darwin explains natural selection

In nature,
organisms
produce more
offspring than can
survive.

In any population,
individuals have
variations. Fishes,
for example, may
differ in color, size,
and speed.

Individuals with
certain useful
variations, such as
speed, survive in
their environment,
passing those
variations to the
next generation.

Over time, offspring
with certain variations
make up most of the
population and may
look entirely different
from their ancestors.
Structural adaptations arise over time

The ancestors of today’s common mole-rats
probably resembled African rock rats.
Structural adaptations arise over time

Some ancestral rats may have avoided predators
better than others because of variations such as the
size of teeth and claws.
Structural adaptations arise over time

Ancestral rats that
survived passed their
variations to offspring.

After many
generations, most of
the population’s
individuals would have
these adaptations.
Structural adaptations arise over time

Over time, natural
selection produced
modern mole-rats.

Their blindness may
have evolved because
vision had no survival
advantage for them.
Structural adaptations arise over time

Mimicry is a structural adaptation that enables one
species to resemble another species.

Predators may learn quickly to avoid any organism
with their general appearance
Structural adaptations arise over time

camouflage, an
adaptation that enables
species to blend with
their surroundings.

Because wellcamouflaged
organisms are not
easily found by
predators, they survive
to reproduce.
Rapid Adaptations



In general, most structural adaptations develop over millions of years.
However, there are some adaptations that evolve much more rapidly.
The evolution of insecticide resistance is an example of natural selection in
action
Evidence for Evolution

Physiological resistance in species of
bacteria, insects, and plants is direct
evidence of evolution.

Biogeography
 Closely related but different
 Distantly related but similar (wolves and dogs)
Evidence for Evolution
Fossils

provide a record of early
life and evolutionary
history.

Although the fossil record
provides evidence that
evolution occurred, the
record is incomplete

As the fossil record
becomes more complete,
the sequences of
evolution become clearer
Comparative anatomy
Homologous
structures:
 Structural features with a
common evolutionary
origin
 Can be similar in
arrangement, in function, or
in both
Comparative anatomy
Analogous Structures:



The body parts of organisms that
do not have a common
evolutionary origin but are similar
in function
Although analogous structures
don’t shed light on evolutionary
relationships, they do provide
evidence of evolution
For example, insect and bird
wings probably evolved separately
when their different ancestors
adapted independently to similar
ways of life.
Comparative Anatomy
Vestigial Structure
a body structure in a
present-day organism that
no longer serves its
original purpose, but was
probably useful to an
ancestor.
 Vestigial structures, such
as pelvic bones in the
baleen whale, are
evidence of evolution
because they show
structural change over
time.

Comparative Embryology


developmental patterns are similar in organisms
with similar evolutionary relationships
The embryos of a fish, a reptile, a bird, and a
mammal have a tail and pharyngeal pouches.
Comparative Biochemistry



Nearly all organisms share
DNA, ATP, and many
enzymes among their
biochemical molecules.
biologists use RNA and
DNA nucleotide sequences
to construct evolutionary
diagrams.
Organisms that are
biochemically similar have
fewer differences in their
amino acid sequences.
Chapter 17 Evolution of
Populations
Populations, not individuals, evolve
• If an organism has a feature—called a
phenotype in genetic terms—that is poorly
adapted to its environment, the organism
may be unable to survive and reproduce.
Populations, not individuals, evolve
• Natural selection acts on the range of phenotypes in a
population.
• Picture all of the alleles of the population’s genes as being
together in a large pool called a gene pool.
• The percentage of any specific allele in the gene pool is called
the allelic frequency.
• Any factor that affects the genes in the gene pool can change
allelic frequencies, which results in the process of evolution.
Mechanisms for genetic change

1. Mutation
 occasionally, a mutation results in a useful
variation, and the new gene becomes part of the
population’s gene pool by the process of natural
selection.

2. genetic drift
 the alteration of allelic frequencies by chance
events.
Natural selection acts on variations
• There are three different types of natural selection that
act on variation: stabilizing, directional, and
disruptive.
Stabilizing Selection
• a natural selection that favors average individuals
in a population.
Selection for
average size
spiders
Normal
variation
Directional Selection
• occurs when natural selection favors one of the
extreme variations of a trait.
Normal
variation
Disruptive Selection
• individuals with either extreme of a trait’s
variation are selected for.
Selection for
light limpets
Normal variation
Selection for
dark limpets
Genetic Drift
In small populations, individuals that
carry a particular allele may leave more
descendants than other individuals
leave, just by chance.
 Over time, a series of chance
occurrences can cause an allele to
become more or less common in a
population
 This is called GENETIC DRIFT

Genetic Bottlenecks
A change in allele frequency following a
dramatic reduction of the population
size.
 Can greatly reduce a population’s
genetic diversity.

The Founder Effect

Allele Frequencies change as a result of
the migration of a small subgroup of a
population.
Genetic Equilibrium

population is not evolving, the allele
frequencies in the gene pool do not
change.
Hardy-Weinberg Principle

Predicts 5 conditions that disrupt genetic
equilibrium and cause evolution to
occur.
1. Nonrandom Mating
2. Small Population Size
3. Immigration or Emigration (introducing new
genes to the gene pool or removing them)
4. Mutations
5. Natural Selections
The Evolution of Species
• Significant changes in the gene pool could
lead to the evolution of a new species over
time.
• The evolution of new species, a process
called speciation occurs when members of
similar populations no longer interbreed to
produce fertile offspring within their natural
environment.
Isolating Mechanisms
 Geographic isolation
○ A new species can evolve when a population has been
geographically isolated.
 Behavioral Isolation
○ Two populations that are capable of interbreeding develop
differences in courtship rituals and other behaviors.
 Reproductive Isolation
○ Populations become reproductively isolated when they
evolve into two separate species
 Temporal Isolation
○ When two or more species reproduce at different times