Evolution
Evolution: the process of change by which new species come about from preexisting species
 the theory of evolution states that organisms alive today are related to extinct organisms that lived in
the past
 population: members of a species that live in a certain region
 the main idea of the theory of evolution is that populations undergo biological changes
over the generations
Fossils are remains or traces of organisms that once lived
 fossils are found in rocks, ice, tar or hardened tree sap called amber
 provide evidence of past animals that have lived on earth
 can be imprints or actual parts of animals
 found in sedimentary rock: rock that forms from buildup of sediments. Layers of sediment dry
harden and form layers of rock called strata. The oldest rock layers are at the bottom , the
youngest are near the surface
 age of the fossil is the same as the age of the rock layer it is found in
 age of a fossil can be determined by finding the age of the rocks they are in or by
dating the fossil itself. Both ways use radioactive dating
 radioactive elements break down into stable non-radioactive elements at a
constant rate. This rate is called the half-life of the element. This is the time
needed for half of a radioactive sample to break down into a non-radioactive
substance.
 ex. Carbon-14 has a half life of 5,710 years. If you begin with 10g of C-14,
after 5,710 years, 5g will be left. After another 5,710 years (11, 420 total),
half of the 5g, or 2.5g will be left.
 Uranium-238 has a half-life of 4.5 billion years.
 Potassium-40 has a half-life of 1.3 billion years.
 C-14 is used to date the fossil itself, but if the fossil is more than 100,
000 years old, the rocks it was found in must be dated because there
will not be enough C-14 left to measure
 Oldest rock strata contain the oldest fossils. The oldest fossils are of simple organisms. Newer
fossils near the surface are more similar to existing species
 Transitional form: an organism that has characteristics in between two other types of
organisms. Transitional forms usually show a link between extinct species and a current one.
 ex. Eohippus is a transitional form of the horse
 Archaeopteryx is thought to be a transitional form between dinosaurs and birds
Comparative Anatomy
Most scientists believe that structural similarities indicate that organisms are descended from a common
ancestor.
 Homologous structures: parts of different organisms that have a similar structure but different
functions. They suggest descent from a common ancestor.
 Ex. The forelimbs of all mammals have the same structure: one bone in the upper part,
two in the lower part, a joint then at least two appendages (fingers)
 this bone structure is also seen in birds and some reptiles and amphibians
 Vestigial structures: organs or body parts that serve little or no function.
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thought to be remnants of organs that were once functional
 ex. Leg bones and pelvic girdle in adult python skeleton
 ex. Tailbone in humans
Analogous structures: have similar functions but different structures
 do not suggest a common ancestor. Instead, they suggest that these organism live in
similar environments and had to respond to the same pressures
 ex. Wings of a butterfly and the wings of a bird, bat ,or flying squirrel
Comparative Embryology
Certain organisms show similarities in the development of their embryos (earliest stages of development)
 at the beginning of development, all vertebrate (animals with backbones) embryos are virtually
identical
 evidence of common ancestry
Comparative Biochemistry
All organisms are made of cells and all cells have the same basic processes:
 energy is stored as ATP
 the DNA of all organisms is made of the same four nucleotides
 all organisms make their proteins from the same 20 amino acids
Some organisms can assemble their amino acids into similar proteins. The more similar the proteins, the
more closely related the organisms are
 the proteins made by gorillas are 99.8% identical to the proteins made by humans
Comparative biochemistry provides evidence of common ancestry
Theories of Evolution
Lamarck’s Theory
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Organs that are used more often would develop more than those that are not used. Called the Theory
of Use and Disuse
 Used theory to explain how giraffes got long necks
 Giraffes all began with short necks. As food got scarce the giraffes stretched their necks
to reach food higher in the trees. They then passed the long necks on to their offspring:
Theory of Acquired Characteristics.
 Not true because a physical change does not affect the genetic code. There would be no way to
pass the longer necks to the offspring. It has to be adaptation to it’s environment.
Darwin’s Theory
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Published a book called On the Origin of Species and in the book Darwin proposed the Theory of
Natural Selection: organisms that are better adapted to their environment will survive longer and
produce more offspring than organisms less suited to their environment
These organisms are genetically better adapted to their environment.
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Darwin did his research on the Galapagos Islands where he observed many different types of birds
called finches. Each island had a different environment and the finches on each island had a beak
adapted to the type of food that grew on the island
 seed eating finches: broad strong beaks
 insect eating finches: longer thinner beaks
Darwin believed the finches originally came from South America and adapted to the dominant type of
food on their island
 all the Galapagos finches resemble each other and resemble the South American finches but they
are all uniquely adapted to their environments
Darwin explained Lamarck’s giraffes by saying that giraffes originally had both long and short necks.
Since the long necked ones were better suited, they survived and reproduced, passing the long neck
trait on to their offspring.
The theory of natural selection can be summarized as follows:
 overproduction: favorable conditions allow a population to increase in size. Eventually, the
environment will limit the size of the population (carrying capacity)
 variation: no two organisms in a population are exactly alike. They differ in size behavior and
other features
 competition: environmental pressures force organisms in a population to compete for food and
mates in order to survive
 survival of the fittest: the best adapted individuals get the most food and the best mates. They
are most likely to survive and pass their variations on to the next generation
 reproduction: individuals that survive and reproduce pass their traits on
 speciation: over time, the population changes because some traits are passed on and some die
out. When the difference from the original population becomes great, a new species forms.
 species: a group of organisms that can interbreed and produce fertile offspring.
 mutations can enter more different traits into the population
Types of Adaptations
Adaptation: an inherited trait that makes an organism better able to survive in an environment
 There are three types of adaptations
 1. morphological: structural traits that make an organism more suited to an environment
 many are related to food getting
 tentacles on jellyfish
 sticky tongue on an anteater
 hollow bones in birds
 colored petals on flowers
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2. physiological: adaptations in the metabolic processes in an organism
 Immunity to drugs or pesticides
 digestive enzymes
 formation of hemoglobin to carry oxygen in the blood
3. behavioral: behaviors that help an organism to survive
 courtship “dances” in insects, birds and fish that allow males and females to recognize
members of their own species
 males fighting over females
Evolutionary theories involving genetics are based on Gradualism & Speciation
Rate of Evolution
Some scientists believe that evolution is a slow, continuous process. This theory is called gradualism.
Some scientists believe that evolution occurs in short burst of rapid change. This theory is called
punctuated equilibrium
 came about to explain apparent gaps in the fossil record
 suggested that the gaps are real because no change was happening. Transitional forms
developed at the end of these dormant periods, and then evolution occurred again
 evolutionary change could occur as quickly as a few thousand years
 the result of a period of punctuated equilibrium would be a new species
 since the new species is theoretically better suited to survive, the older species will
not be able to compete. Eventually it will die out and become extinct.
Speciation
Speciation is the process where new species evolve from ancestral species
 in order for a new species to form, members of a population must in some way become separated from
other members of the population
 geographic isolation: happens when a physical barrier (mountains, seas, etc.) stops members of
two populations of the same species from interbreeding
 different environmental pressures may exist as a result of the barrier
 ex. Desert on the leeward side of a mountain
 over time the populations become different and can no longer interbreed and produce
fertile offspring
 even if the barrier is now removed, the two populations will not interbreed
because of differing breeding seasons, courtship rituals or even genes. If this
occurs, reproductive isolation has occurred.
 could explain the finches on the Galapagos Islands. The islands are far removed
from the coast of Ecuador and from each other
Population Changes
Population genetics applies the genetic principles of individuals to groups of individuals
 in modern times, the term evolution does not apply to a change in an individual, but to a change to all
members of a population.
 gene pool: the whole genetic makeup of a population. The gene pool includes all the genes of all
the members of a population
 gene frequency: the number of times an allele for a particular trait appears in the gene pool
 genetic equilibrium: occurs when the gene frequencies remain the same from one generation to
the next.
 no evolution is taking place
 changes in gene frequency will only occur if the gene frequency is disrupted, so anything
that causes a change in gene frequency will cause evolution
Hardy-Weinberg Law
States that the gene pool of a sexually reproducing population will remain stable (no evolution will occur) if
all the following conditions are met: (Average Individuals are favored)
 large population. This insures that chance mutations alone will not change the gene frequency
 there is no movement of organisms into or out of the population
 there are no mutations
 reproduction is totally random. Natural selection does not favor one allele for a trait over
another
Since these circumstances cannot all take place at once the conditions for evolution are always present
 any change in the gene pool caused by chance (ex. accidental death) is called genetic drift
 Gene flow is the movement of alleles into or out of a population
 gene flow can cause a change in gene frequency and can cause evolution
Patterns of Evolution
There are two patterns of evolution
 Divergence: as time passes, the descendants of a common ancestor become less and less alike
showing variations over time. Variety = Diversity
 adaptive radiation: the rapid evolution of many new species, usually within the time span
of a few million years (this is fast) is a type of divergent evolution
 the new species radiate or branch outward from a small number of species
 adaptive radiation usually follows mass extinctions: the sudden disappearance of
many species at the same time
 usually is a result of responding to different environmental pressures and geographic
isolation
 may still be alike in many ways, their differences are significant
 ex. Variety in color and beak shape of some birds
 ex. horses, donkeys and zebras all descend from the same ancestor
 ex. brown bear, grizzly bear and polar bear
 Convergence: an increased similarity over time among unrelated species derived from different
ancestors because they all show similar adaptations to similar environments.
Similarity = Conformity
 ex. fish and dolphins
 ex. Marsupials & Placental mammals