Download Evolution--Darwin 2016_Mitchell

Evolution
• Theory- a well-supported testable explanation of
phenomena that have occurred in the natural world.
• Evolution- Change over time; modern organisms
have descended with modification from ancient
organisms.
 Because it is supported by so many lines of
evidence, evolution is no longer considered a
hypothesis. Evolution is one of the great unifying
theories of biology
What was Charles Darwin’s
contribution to science?
• At 22, sailed on the
“HMS Beagle” to the
Galapagos Islands.
• Was going to school to
be a minister-believed
God created each
species to match its
habitat and they never
changed.
• Thought Earth was about
6,000 years old and
didn’t change.
• During journey, he
made observations
and recorded them in
a journal.
• Darwin began to
doubt that species
remained “constant.”
Darwin’s Background Voyage
• Darwin's many observations led him to the idea that species
slowly change over time
• Darwin's comparison of the animals of South America and
the Galapagos Islands caused him to conclude that
adaptation to the environment can cause diversification,
including origin of new species
• Examples: Patagonian hares replaced rabbits in the South
American grasslands
The Galapagos Islands
Island species varied from the mainland species, and
from island-to-island
Each island had either long or short necked tortoises
depending on the island's vegetation
Darwin’s Observations Contd.
Finches found only on the Galapagos Islandsresembled a mainland finch, but there were more
types
Beak shapes are adaptations to different means of
gathering food (what the finches eat)
Galapagos finch species varied by:
nesting site
beak size
eating habits
The Galapagos Islands
The diagram below presents 10 species of finches on the
Galapagos Islands, each filling a different niche on various
islands.
All of them evolved from one ancestral species
Each species evolved from the same ancestor through
process of geographic isolation
• In 1859, Darwin published
“The Origin of Species.”
• His book stirred up
controversy.
• Proposed **EVOLUTION
OCCURRED BY NATURAL
SELECTION
• Organisms have more offspring than can
survive.
• Certain individuals are more likely to survive
than others (survival of the fittest.)
• Species DO change over time.
• Gradual changes may cause members of one
species to eventually evolve into new species.
• African apes are close genetic relatives of
modern humans.
Darwin’s Insights
Members of each species vary from one another
 Artificial selection- selection by humans for
breeding of useful traits from the natural
variation among different organisms
 Artificial selection is used to breed animals
with the trait of interest
In artificial selection, nature provided the
variation, and humans selected those
variations that they found useful
Lots of change can be achieved in a relatively
short time
Artificial Selection
What ideas shaped Darwin’s
thinking?
Hutton and Lyell helped scientists
recognize that Earth is many millions of
years old, and the processes that
changed Earth in the past are the same
processes that operate in the present
Hutton and Lyell proposed that
geological processes have shaped
the Earth, ex. Rain
LaMarck’s Theor
• Jean Baptiste LaMarck: 1800’s
– Believed:
• Change Occurs Over Time
• Inheritance of acquired
characteristics
– acquired changes were
passed to offspring
• Law of Use and Disuse
– If a body part were used, it
got stronger
– If body part NOT used, it
deteriorated
• Examples: Body builders or
pierced ears
Thomas Malthus
• 19th century English economist
Malthus reasoned that if the
human population continued to
grow unchecked, sooner or later
there would be insufficient living
space and food for everyone
Darwin’s Principles of Natural Selection
Natural selection is the mechanism by which evolution occurs
1. Variations exist between individuals in a species.
2. Variations are inherited from parents.
3. Populations produce more offspring than can
survive on the available resources.
4. Variations that increase reproductive success will
be more common in the next generation.
Given enough time, natural selection could modify a
population enough to produce a new species.
Darwin’s Evidence for Evolution
1. Fossil record
-fossils are remains or imprints of living things
-different layers of rock were formed at
different times in Earth’s history
-comparing fossils from older layers to fossils
from younger layers shows that organisms
change over time
Darwin’s Evidence, continued
2. Geographic Distribution
of Living Species
- geographically separate,
similar species (like
finches) descended with
modifications (changes)
from a common ancestor
-geographically separate,
similar environments
gave rise to different
species that had similar
anatomy and behavior
3. Comparative Anatomy
Homologous body structures:
-structures that have different mature forms but
develop from the same embryonic tissues
-have strong structural similarities between
different species
-adapted in different ways to help survive in
different environments
-provide strong evidence that there is descent
from common ancestors
-vestigial structure is a trace of homologous
structures that have little or no function
Anatomical Evidence cont.
Analogous structures – different structures that
are inherited from different ancestors and have
come to resemble each other because they serve
a similar function
• Do not come from the same evolutionary
origin
• Ex: wings of birds vs. wings of insects
• Ex: fins of fish vs. flippers of whales
Different structure, same function!
4. Comparative Embryology:
-there are many similarities in embryos of many
vertebrate animals
-provides strong evidence of common ancestry
5. Comparative Biochemistry
-common ancestry can be seen in complex
metabolic molecules
-species that share a recent common ancestor
share some amino acid sequences
-the more closely related the species are, the more
sequences will be shared
-this has been found to be true with cytochrome c,
an enzyme essential for respiration in animals
-similar patterns have been found in other proteins
as well as in DNA and RNA
Adaptation
• The concept of adaptation underlies Darwin’s
theory of natural selection.
• An adaptation is a trait shaped by natural
selection that increases an organism’s survival
or reproductive success. (Fitness)
• Examples:
– Camouflage: blend with surroundings
– Mimicry: look like another species
– Antimicrobial resistance: in bacteria
Population Genetics
• Evolution occurs at the population level, not the
individual. Genes are the raw material for
evolution.
• Evolution won’t occur in a population unless the
frequencies of alleles are acted upon by forces
that cause change.
• (Constant allele frequencies = genetic equilibrium)
Disruptions to Genetic Equilibrium
(Mechanisms of Evolution)
• Genetic Drift: any change in the allele
frequencies that is due to chance. It has the
greatest effect in small populations due to
the small gene pool size.
– Founder Effect: extreme example of genetic
drift. Occurs when a small part of a population
becomes isolated from the rest of the
population. The random subset of alleles in the
small population may become more common,
and result in genetic variations in the separated
populations. Examples: Amish communities
with polydactyly and dwarfism.
– Bottleneck: extreme example of genetic drift.
Occurs when a population declines to a very
low number and then rebounds. Gene pool of
the rebound population is genetically similar
to the lowest level of population—it lacks
diversity.
• Gene flow: New genes entering the
population and other genes leaving the
population as individuals randomly
move (migrate) between populations.
• Nonrandom mating: Organisms usually
mate with individuals in close proximity.
This can lead to inbreeding and a change
in allele frequencies.
• Mutation: a random change in genetic
material. The cumulative effect of
mutations in a population might cause a
change in allele frequencies. Beneficial
mutations could be selected for, and
become more common in subsequent
generations.
• Natural selection: acts to select the
individuals best adapted for survival and
reproduction. It acts on an organism’s
phenotype, and changes allele
frequencies.
Speciation
Speciation is the formation of new species.
A species is a group of organisms that can
breed with one another and produce fertile
offspring.
This means that individuals of the same species
share a common gene pool, and a genetic
change that occurs in an individual can spread
throughout the population as that individual and
its offspring reproduce.
Speciation continued
For a species to evolve into two new species, the
gene pools of the two populations must become
separated. This means the populations must be
reproductively isolated: the members of the two
populations can’t interbreed and produce fertile
offspring.
There are several ways reproductive isolation can
occur.
Speciation, continued
1.
Behavioral Isolation:
-two populations are
capable of
interbreeding but have
different courtship
rituals or reproductive
strategies that involve
behavior
2. Geographic Isolation:
-two populations are
separated by geographic
barriers
-this can result in
separate gene pools
Speciation, continued
3. Temporal Isolation:
-two or more species reproduce at different
times
Once the populations are isolated, natural
selection works on each population differently,
eventually resulting in enough differences so
that successful interbreeding can’t occur. At this
point, the populations are separate species.
Patterns of evolution
• Adaptive radiation
– Also called divergent evolution
– Occurs in a relatively short time when one species
gives rise to many species in response to creation of
new habitat or other ecological change
– Example: rise of the mammals after the extinction of
dinosaurs
• Coevolution
– Species evolve in close relationship with other
species—evolution of one affects the other
– Examples: can be mutually beneficial, can be
parasitic
• Convergent evolution:
– Unrelated species evolve similar traits in different
parts of the world
– Occurs in ecologically similar environments that are
geographically separate
Rates of Speciation
• Gradualism: evolution
proceeds in small, gradual
steps
• Punctuated equilibrium:
long periods of no
changes are punctuated
by short, rapid periods of
genetic change