Transcript Evolution: A history and a process

Evolution: A history and a
process
Charles Darwin=
Father of the Theory of Evolution
• Evolution= all of the changes that have
transformed life over an immense time
• Two ideas persisted before Darwin
– Species are fixed
– Earth was less than 10,000 years old and
also unchanging
Before Darwin…
• 1800s Jean Baptiste Lamarck
– Proposed that life evolves and that
species are not permanent
– Process of adaptation
Other scientists
• Charles Lyell- geologist
– Proposed the gradual and observable
geologic processes
• Erosion, formation of mountains
– Darwin confirmed this when he witnessed
an earthquake in Chile that moved a
portion of land above sea level
• Thomas Malthus
– Proposed that a population’s growth is
influenced by resources
• Darwin left England as a young graduate
• He returned as a famous naturalist
• 1844 Darwin wrote a 200 paper essay that
described his idea…but was not published
• 1858 Alfred Wallace came to the same
conclusions as Darwin
• Within a month, some of Wallace’s, as well
as Darwin’s ideas, were presented to the
public jointly
• One year later, Darwin published his book
The Origin of Species
•
Darwin made two points in his book:
1. Species on Earth today descended from
ancestral species
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These descendants spread into different
habitats around the world and acquired
adaptations for a diversity of life
“Descent with modification”
Ex: jackrabbit and showshoe hare
2. Natural selection is the mechanism for
evolution
•
Natural selection is the process by which
individuals with inherited characteristics that
are ideal to the environment leave more
offspring on average than do other
individuals
Evolution leaves signs
• Evolution leaves evidence in
– The fossil record
– The diverse assortment of modern species
• Fossil record
– Fossils= preserved remains or markings left by
organisms that lived in the past
• Found mostly in sedimentary rocks
• Sedimentation causes rock formation as particles
accumulate in layers; any given stratum (layer) is older
than the one above it, and younger than those below
• Paleontologist= scientist who studies
fossils
• Oldest fossil evidence of life consists
of chemical traces in rocks that are 3.8
billion years old
– Found in Greenland
• Prokaryote fossils have been found and
dated as 3.5 billion years old
• Fossil example:
– Basilosaurus= an early whale found to
have remnants of hind leg bones
• Geographic Distribution
• Darwin observed the similarities and
differences of organisms from different parts
of the world
– Darwin proposed that organisms present today
evolved from ancestral forms
• Geographic distribution can be used as a
clue for the evolution of species
• Biogeography is the study of the distribution
of plants and animals throughout the world
• The world’s six biogeographical regions
have their own distinct mix of living things
• Continental drift refers to the changing
positions of the continents over time
• Two hundred twenty-five million years ago,
all the present land masses belonged to one
continent (Pangaea)
• The distribution of plants and animals is
consistent with continental drift
• Organisms, such as certain seed plant
groups or reptiles, are widely distributed
throughout the world
• Other groups, such as mammals that arose
after the continents broke up, have great
differences in species on different continents
• Clues to evolutionary history
– Similarities in Structure
– Example: mammal forelimb
– Homologous structures= similar
structures in species haring a common
ancestor
• “Descent with modification”
• Proposed by Darwin
• Modification of structures to take on
new functions
• Vestigial structures= remnants of
structures that may have served an
important function in an ancestral
species, but have no clear function in
some of the modern descendents
– Often smaller in size
• Ballene whale
• Developmental similarities
• Embryos of closely related species have similar
stages of development
• Bones of the skeleton form in a common pattern
• The process of comparing how certain structures
develop in different organisms is comparative
embryology.
• Molecular biology
– Comparison of DNA sequences
between species
– If the two species’ sequences match
closely then it is thought that the two
species are related to a common
ancestor
– If the two species’ sequences have
many differences they probably do not
share common ancestry
Comparison of Hemoglobin
• Artificial selection= selective breeding of
domesticated plants and animals to produce
offspring with genetic traits that humans
value
• Munchkin cats
Artificial Selection
Collie
Sheltie
• In contrast, natural selection favors
traits that are beneficial to the
organisms in their environment
• The environment does the “selective
breeding”
• Resulting in evolutionary adaptation
Natural Selection of Flies
• Darwin could not explain how variations
passed from one individual to the next
• Gregor Mendel to the rescue!!
– Microevolution…a change in a population’s gene
pool
– Gene pool= consists of all the alleles in all the
individuals that make up a population
• Where genetic variation is stored
• Example: Wild mustangs
– What leads to genetic variation?
• Mutations
• Sexual recombination
• Natural selection is not random
• Why?
– The environment favors combinations of genes
that contribute to survival and reproductive
success
– Some alleles may become more common in a
gene pool than others
• Frequency of alleles= how often certain alleles occur in
the gene pool
– Usually expressed as a percentage
• Microevolution
– Blending of Mendel’s and Darwin’s theories to
look at evolution based on genetics
– Generation to generation changes (smallest scale)
Microevolution
•
What causes gene pools to change
(besides natural selection)?
1. Genetic drift= a change in the gene pool
of a population due to chance
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All populations are subject to genetic drift
Bottleneck effect…a drastic reduction in the
size of a population
– Usually by natural disaster…and only a few
remaining individuals are left to start a new
population
• Ex: cheetah population in Africa
•
Founder effect…genetic drift in a new colony
– When a few individuals leave the original
population and start a new population
Genetic Drift
• 2. Gene flow= movement of alleles
between populations
– Occurs when fertile individuals mate with
individuals from other populations
– Ex: a wind storm might blow pollen from a
population of only red flowers to a
population consisting of only white
flowers
– Reduces the genetic differences between
populations
– Can eventually mix the two populations
So how did humans evolve?
• A very lengthy process in
which people originated
from apelike ancestors.
• The evolution of humans
has occurred over the last
6 million years.
• Bipedalism – walking on
2 legs – 4 million years
ago
• Most advanced traits
have occurred over the
last 100 million years.
• Apes have a very
large, very strong
lower jaw to support
their carnivorous
eating.
• As the shape of the
human skull evolved
to have a smaller
lower jaw, this allowed
for a larger brain to
develop.
• With a larger brain,
the capacity for
language and the
manufacture of tools
were able to be
developed.
• Fitness = the contribution that an
individual makes to the gene pool of
the next generation compared to the
contributions of other individuals
So what does “survival of the fittest” mean?
How does 1 species become
2 species?
Species = a population or group of populations whose
members can interbreed and produce fertile
offspring
– Speciation = the formation of a new species
Reproductive isolation = when populations become
reproductively isolated, they can evolve into two
separate species
• Interbreeding links members of a species
genetically
• If the members stop interbreeding, then the
gene pool can split
3 ways Reproductive Isolation
can develop
1. Behavioral isolation = when two
populations develop differences in
courtship rituals or other behaviors
that prevent them from interbreeding
•
Eastern and Western Meadowlarks don’t respond to
eachothers songs
3 ways the reproductive isolation
can develop
2. Geographic isolation = when two
populations are separated by
geographical barriers (rivers,
mountains, bodies of water)
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Grand Canyon isolated a small population of Albert’s
squirrel on the northern rim
Separate gene pools formed, natural selection and
genetic drift worked separately on each group which
led to the formation of a distinct subspecies called the
Kaibab Squirrel
3 ways the reproductive isolation
can develop
3. Temporal isolation = when two or
more species reproduce at different
times of the day, season, or year
Species of Organisms
• There are 13 billion known
species of organisms
• This is only 5% of all organisms
that ever lived!!!!!
• New organisms are still being
found and identified
What is Classification?
• Classification = is the arrangement
of organisms into orderly groups
based on their similarities
• Classification is also known as
taxonomy
– Benefits:
• Accurately and uniformly names organisms
• Prevents misnomers
– Ex: jellyfish, seahorse
Confusion in Using Different
Languages for Names
Latin Names are Understood
by all Taxonomists
Carolus Linnaeus
1707 – 1778
• 18th century
taxonomist –
“Father of
Taxonomy”
• Classified
organisms by
their structure
• Developed
naming system
still used today
Standardized Naming
• Two-word name
(Genus & species) =
Binomial
Nomenclature
• Latin or Greek
• Genus is
capitalized, species
is not
• Italicized in print
• Underlined if
handwritten
American Robin
Turdus migratorius
Binomial Nomenclature
Which TWO are more closely related?
Rules for Naming Organisms
• The International Code for
Binomial Nomenclature contains
the rules for naming organisms
• All names must be approved by
International Naming Congresses
(International Zoological
Congress)
• This prevents duplicated names
Classification Groups
• Taxon ( taxa-plural) is a category
into which related organisms are
placed
• There is a hierarchy of groups
(taxa) from broadest to most
specific
• Domain, Kingdom, Phylum,
Class, Order, Family, Genus,
species
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Hierarchy – Taxonomic
Groups
BROADEST TAXON
• Domain
• Kingdom
•
Phylum
•
Class
•
Order
•
Family
•
Genus
MOST
•
Species
SPECIFIC
• Dumb
• King
• Phillip
• Came
• Over
• For
• Gooseberry
• Soup!
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Domains
• Broadest, most inclusive taxon
• Three domains
• Archaea and Eubacteria are
unicellular prokaryotes (no
nucleus or membrane-bound
organelles)
• Eukarya are more complex and
have a nucleus and membranebound organelles
Cladogram
• Diagram showing how organisms are
related based on shared, derived
characteristics such as feathers, hair,
or scales
Primate
Cladogram
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Dichotomous Keying
• Used to identify organisms
• Characteristics given in pairs
• Read both characteristics
and either go to another set
of characteristics OR identify
the organism
Dichotomous Key
•1a Tentacles present – Go to 2
•1b Tentacles absent – Go to 3
•2a Eight Tentacles – Octopus
•2b More than 8 tentacles – 3
•3a Tentacles hang down – go to 4
•3b Tentacles upright–Sea Anemone
•4a Balloon-shaped body–Jellyfish
•4b Body NOT balloon-shaped - 5