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Evolution
Science Before Darwin
• Before Darwin, most people believed that
species existed exactly as they were
created by a divine creation.
• Scientists began to seek explanations for
the origins of fossils.
• This began the idea that living things
changed over time.
Jean Baptiste Lamarch
• Proposed hypothesis for how organisms
changed over generations.
• He believed: over the lifetime of an
individual, physical features increase or
decrease in size because of its use or
disuse. These features were then passed
on to offspring.
• What he did get right: environmental
conditions affect species.
Lamarck’s Theory
Charles Darwin
• Naturalist
– Sailed around the world on the HMS Beagle
• Found evidence that species evolve, or
changed over time, and that was the basis
for life’s diversity.
• Conducted his study of plants and animals
on the Galapagos Islands off of South
America.
Darwin
• Developed the most accepted theory of
evolution.
– Father of Evolution
• He explained the process of evolution
through natural selection.
Evolution by Natural Selection
• Most organisms can produce more
offspring than can survive.
• Organisms differ from place to place
because of their habitats.
• Individuals that have physical or
behavioral traits that better suit their
environment are more likely to survive and
will reproduce more successfully than
those that do not have such traits.
Evolution by Natural Selection
• This “survival of the fittest” is the driving
force behind the change in a species.
– Natural Selection
• In time, the number of individuals with
favorable characteristics will increase in a
population.
• Therefore, the nature of the population
changes-evolution.
Evolution by Natural Selection
• Each species that has evolved has
accumulated adaptations in response to
their environment.
– Adaptations are some feature that has a
selective advantage
Plant Adaptations
• Desert plants have modified structures to
allow them to survive better in their hot,
dry climate
• Examples:
– Stomata (pores) that only open at night when
it is cooler
– Thorns for protection
– Waxy covering to reduce water loss
– Fine, hair like fuzz to protect against wind and
sun
– Small leaves they drop in severe drought
Mimicry vs. Camouflage
• Mimicry
– The resemblance of one organism to another
or to an object in its surroundings for
concealment and protection from predators
• Camouflage
– Concealment by disguise or protective
coloring so as to make the wearer
indistinguishable from the surrounding
environment
Monarch Butterfly
Viceroy Butterfly
Coral Snake
Colubrid Snake
Species Formation
• Environments differ from place to place
– Temperature, food available, amount of space
• Populations of the same species living in
different locations tend to evolve in
different directions.
• As two isolated populations of the same
species become more different over time,
they may eventually become unable to
breed with one another.
– Reproductive Isolation
– The two populations then become 2 separate
species
Species Formation
The ecological niches exert the selection pressures that push the
populations in various directions.
Species Formation
• Sometimes unrelated species become more
similar as they adapt to the same kind of
environment
– convergent evolution
• They've evolved similar adaptations because they
occupy similar niches -- dining on ants, hunting in
the high grass, or swimming in the dark
• Ex: the different sorts of anteaters, found in
Australia, Africa, and America. Though not closely
related, they all evolved the "tools" necessary to
subsist on an ant diet: a long, sticky tongue, few
teeth, a rugged stomach, and large salivary glands
Darwin’s Theory
• Variations exists within the genes of every
population or species.
– Ex: eye color, fur color, size, beak shape
Darwin’s Theory
• In a particular environment, some
individuals of a population or species are
better suited to survive (result of variation)
and have more offspring (natural
selection)
Darwin’s Theory
• Over time, the traits that make certain
individuals of a population able to survive
and reproduce tend to spread in that
population.
Darwin’s Theory
• There is overwhelming evidence from
fossils and many other sources that living
species evolved from organisms that are
extinct.
Tempo of Evolution
• Gradual changes over LONG periods of
time
– Gradualism
– Most accepted
• The thought that successful species may
stay unchanged for long periods of time
then evolution occurs in spurts because of
major environmental changes in the past
– Punctuated Equilibrium
Evidence of Evolution
• Homologous Structures
– Similar physical structures that share common
ancestry
Homologous Structures
Homologous Structures
Evidence of Evolution
• Analogous Structures
– Structures that are similar but evolved
SEPERATELY, NOT from a common
ancestor
– Occur because of convergent evolution
Vestigial Structures
• Vestigial Structure
– A structure in an organism that is reduced in
size and function that may have complete and
functional in an ancestor
Vestigial Structures
Evidence of Evolution
• Fossil Records!
Archaeopteryx (left) and a pigeon (right).
Evidence of Evolution
• Biological Molecules
– Proteins
• Amino acids linked together make proteins
• Species that have fewer differences in between the
sequence of amino acids share a common
ancestor
– Nucleic Acids
• Nucleic acids linked together form DNA
• Species that have fewer differences in the
sequence of nucleic acids share a common
ancestor
Evidence of Evolution
• Embryonic Development
Example of Evolution
• Antibiotic Resistant Bacteria
– Mutations (changes) in the nucleotide
sequence (DNA) of the bacteria change the
way the bacteria grows, eats, and behaves
allowing it to grow in the presence of
antibiotics
MRSA (Methicillin-Resistant Staphylococcus Aureus)
Development of a New Species
• Over time, variations that arise within a
population as a result of natural selection
can have 2 major outcomes:
– Speciation
• The accumulation of differences between groups
(divergence) forms a new species
– Extinction
• A species that could no longer survive in their
current environmental conditions and dies out
completely
Populations can Evolve through:
• Genetic Drift
– Random change in allele frequency in a
population due to a chance event
– Ex: a fire or landslide could reduce the
population to only a few individuals; if just one
of the individuals is lost it can have major
effects in the frequency of an allele
– Cheetahs have been seriously affected by this
due to their drastic population decline and
most cheetahs alive today are direct
descendants of only a few individuals
Populations can Evolve through:
• Nonrandom Mating
– Individuals prefer to mate with others that live
nearby or are of their own phenotype
– Inbreeding (mating with relatives) is an
example that causes a lower frequency of
heterozygotes but increases frequency of
homozygotes
• Self-fertilizing plants fall in this category
– Also occurs when organisms choose their
mate based on certain traits (size, color,
ability to gather food, etc)
Populations can Evolve through:
• Gene Flow
– Movement of genes into or out of a population
due to interbreeding
– Individuals will move into or out of a
population (migration) and will add alleles to
the population or remove them
– Ex: when wind carries seeds far beyond the
bounds of the parent plant population the
genes are removed from the original
population and then added to the new
population
Populations can Evolve through:
• Genetic Mutation
– Any change in the sequence of a DNA strand
due to chance or environmental causes
• Natural Selection
– Organisms better adapted to their
environment and have favorable variations
will be more likely to survive, reproduce, and
pass on those traits thus increasing the
frequency of those traits in a population