Download Natural Selection

EVOLUTION
Lamarck
French scientist
 Late 1700’s- early 1800’s

 “acquired
traits” theory:
traits are not determined by genes but
by “need”
 EX: giraffe necks grow longer because
they stretch to reach the leaves higher up.
Lamarck’s Concept
Charles Darwin
 1809-1882
 born
to a wealthy
English family
 went to medical
school, but
earned a degree
in theology
 took
a job as a naturalist on the
ship, H.M.S. Beagle
 one
of the places he visited
were the Galapagos Islands
 he observed tortoises that were
so different, he could identify
which island they lived on

 he
saw two distinct different
types of iguanas that have
evolved so differently that they
no longer belonged to the same
species
 he
saw birds
that were all
finches, but
whose beaks
were adapted
to eat
different food
 knowing
the Galapagos Islands
were volcanic and recently formed,
the life there must have come from
the mainland
 But why were the animals on the
Galapagos so different????
 "At last gleams of light have come,
and I am almost convinced (quite
to the contrary to the opinion I
started with) that species are not
immutable."
 after
consulting with other
scientists and researching,
Darwin believed species
evolved to fit into their habitats
and called it natural selection
 he wrote The Origin of Species
explaining his hypothesis of
natural selection
Darwin’s Natural Selection
4 Main Principles
 (1)In
every population, variation
exists within the inherited traits
of the individuals
 (2)
More offspring are produced
than can survive
 (3)
Individuals with beneficial traits
(have adaptations) have a higher
survival rate than those less
adapted
 (4) Each species will have
descended, with adaptations or
modifications, from previous
generations
(descent with modification)
In 1973, Theodosius Dobzhansky wrote
an essay “Nothing in Biology Makes
Sense Except in the Light of
Evolution.”
 Evolution of biology’s unifying theme
that connects together genetics,
ecology, taxonomy, etc.

Organisms must have a way of
passing information to offspring
Sexual reproduction – production of
gametes through meiosis; fertilization
results in an embryo with genes from
each parent (results in variation)
 Asexual reproduction – one parent
produces an offspring (offspring are
genetically identical)


If the genetic change increases fitness, it
will eventually be found in many
individuals in the population.
Diversity is important for survival
of a population
A species is a group of organisms that
share similar characteristics and can
interbreed with one another to produce
fertile offspring
 Because of a shared gene pool, a
genetic change that occurs in one
individual can spread through the
population

FACTORS THAT INFLUENCE
GENETIC VARIABILITY





Genetic drift – random change in a
population’s gene pool due to chance
Gene flow – movement of genes into or out
of a population (such as migration)
Non-random mating
Mutations
Natural selection – allows for the most
favorable genotype to survive
HARDY-WEINBERG PRINCIPLE

When there is no change in gene
frequency, the population is in genetic
equilibrium
5 conditions are required to
maintain genetic equilibrium
Large population size (no genetic drift)
 No immigration or emigration
 Random mating
 No mutations
 No natural selection (all genotypes
have equal chance to survive)

Microevolution
 small
changes in a population
that take place quickly and can
be documented; for example,
antibiotic resistance in bacteria
or change in peppered moths
Macroevolution
 large-scale
evolutionary
changes that take place over
long time periods
 fossils are evidence of
macroevolution since there
is no human documentation
Horse Fossil From 55 Million
Years Ago
Horse Fossil From 52-45 Million
Years Ago
Horse Fossil from 32-25 Million
Years Ago
Horse Fossil From 17-11 Million
Years Ago
Horse Fossil From 5 Million
Years Ago
Evidence for Evolution
 Paleontology
- fossil record (fossils
are any evidence of life, such as bones,
amber, imprints, etc.)
The fossil record provides evidence
of life forms along a timeline and
supports evolutionary relationships
by showing similarities between
current and ancient species.
Paleontology Continued

The fossil record is not complete,
because most organisms do not form
fossils.

Transitional fossils show links in traits
between groups of organisms used to
document intermediate stages in the
evolution of a species
Evidence for Evolution

Biochemistry - analysis of DNA base
sequences and amino acid sequences
in proteins
 Remember
there are only 4 different
nitrogen bases in DNA
 Used to compare humans to other
organisms

Embryology – comparing embryos of
different organisms
DO YOU KNOW WHAT
ANIMAL THIS IS?
Evidence for Evolution
 Analogous
serve
structures
the same function in
different species but they
evolved independently
rather than from the same
structures in a common
ancestor.
Example of ANALOGOUS
STRUCTURES
Evidence for Evolution
 Homologous
structures
characteristics
shared by
related species because
they have been inherited in
some way from a common
ancestor.

For example, the bones on the front fins of a
whale are homologous to the bones in a
human arm and both are homologous to the
bones in a chimpanzee arm.
Evidence for Evolution
 Vestigial
have
structures
no apparent function, but
resemble structures their
presumed ancestors had. For
example, the human appendix or
the pelvic bones of a whale.
SPECIATION – FORMING A NEW
SPECIES
 New
species form when organisms
are isolated or separated
 Once isolation occurs, genetic
variation and natural selection
increase the differences between
the populations
TYPES OF ISOLATION
Temporal – members of different
populations don’t mate (closely related
species of plants produce pollen during
different times of the year)
 Behavioral – differences in courtship or
mating behaviors
 Geographic – physical barriers divide a
population

PATTERNS OF EVOLUTION
– changes that take
place over long periods of time
(take place gradually)
 Punctuated equilibrium – periods
of abrupt changes after long
periods of little change
 Gradualism
PATTERNS OF EVOLUTION
 Adaptive
radiation (divergent
evolution) – species diverge (split
off) from a common ancestor
 Convergent evolution – organisms
living in similar habitats have
similar appearances and/or
behaviors
PATTERNS OF EVOLUTION
Coevolution – two species change in
response to each other
 Extinction – elimination of a species
Gradual extinction – occurs at a
slow rate
Mass extinction – very sudden
extinction from a catastrophic event

PHYLOGENETIC TREES
Diagram that represent the phylogeny
(evolutionary history) of a species
 It classifies organisms into major taxa
(groups) based on evolutionary
relationships
 Species are classified according to the
order in which they descended from a
common ancestor.

Some trees show the order of
divergence and don’t show relative
time frames
Some indicate an estimated time of
divergence
Tree drawn by Charles Darwin
Taxonomy

The classifying of organisms
 Constantly

changing
The current system includes:
3
domains (Bacteria, Eubacteria, and
Eukarya)
 6 kingdoms (Eubacteria, Archaebacteria,
Protista, Fungi, Plantae, and Animalia)