Download Chapter 13 - Biloxi Public Schools

Chapter 13
The Theory of Evolution
Section 13.1
THE THEORY OF EVOLUTION BY
NATURAL SELECTION
• The idea that life evolves was first
proposed by a Roman named
Lucretius who lived about 1,900
years before the modern theory of
evolution.
• The theory of evolution has
developed through decades of
scientific observation and
experimentation. The modern
theory began to take shape as a
result of the work of Charles Darwin.
• In 1831, Darwin was asked to voyage
on the HMS Beagle as an unofficial
naturalist. What he found would
challenge the traditional belief that
species are unchanging.
What Darwin Saw During His Voyage
• Galapagos Islands – Darwin
found signs that species
evolve. He was struck by the
fact that the flora(plants) and
fauna(animals) of the islands
and those of the nearby coast
of South America resembled
each other.
• Darwin proposed that the
ancestors of Galapagos
species must have migrated to
the islands from South
America long ago and
changed after they arrived.
Darwin Sought a Reasonable Explanation for
Evolution
• The key that unlocked Darwin’s
thinking was an essay written in 1798
by Thomas Malthus.
• Malthus pointed out that the human
population grew faster than food
supply (human pop. grew
exponentially while food increased
arithmetically) . If human
reproduction was left unchecked,
people would cover the world.
• We don’t because of things like
disease, war, and famine that will slow
population growth.
• Population – all the individuals of a
species that live together in one place
at one time. Ex. The population of
deer in Vancleave, MS.
Natural Selection
• Darwin realized Malthus’s ideas apply to all species. Every
organism has the potential to produce many offspring
during its lifetime. In most cases, only a limited number of
those offspring survive to reproduce.
• Individuals that have physical or behavioral traits that
better suit their environment are more likely to survive and
reproduce than those that do not have such traits.
–Charles Darwin
• Natural selection – process by which populations change
in response to their environment.
• Darwin suggested that organisms differ from place to
place because their habitats present different challenges
to, and opportunities for survival and reproduction.
• Adaptation – the changing of a species that results in its
being better suited to its environment
Darwin’s Ideas Have Been Updated
• Best suited to survive and do
well in their environment =
most offspring with the traits
of the better suited parents.
Certain forms of a trait become
more common in a pop.
because more individuals in
the population carry the alleles
for those forms. Natural
selection causes the frequency
of certain alleles to increase or
decrease over time.
• Environments differ from place
to place, so populations of the
same species living in different
places ten to evolve in different
directions.
Isolation–
condition in which
two populations of
the same species
cannot breed with
one another due to
changing.
Extinction Leads to Species
Replacement
Over time, events such as climate
changes and natural disasters result in
some species becoming extinct, which
means that they disappear
permanently. Species that are better
suited for the new conditions will
replace the others.
Section 13.2
EVIDENCE OF EVOLUTION
FOSSILS PROVIDE AN OBJECTIVE
RECORD OF EVOLUTION
Darwin’s theory is almost universally
accepted. Based on a large body of
supporting evidence, most scientists agree
on the following major points:
1.Earth is about 4.5 billion years old.
2.Organisms have inhabited Earth for most
of its history.
3.All organisms living today evolved from
earlier, simpler life-forms.
• However, the fossil record (and so the record of
evolution) is not complete. Many species have lived
in environments where fossils do not form. Even if
an organism does live in good fossil-making
environments, the chances are slim that its dead
body will be buried in sediments before it decays.
• Although the fossil record will never be complete, it
presents strong evidence that evolution has taken
place. Paleontologists, scientists who study fossils,
can determine a fossil’s age fairly accurately using
radiometric dating.
• Radiometric dating enables paleontologists to
arrange fossils in sequence from oldest to youngest.
When this is done, orderly patterns of evolution can
be seen.
Biological Molecules Contain a Record of
Evolution
• If species change over time, then the genes that determine their
characteristics should have also changed (new taller giraffes, no
stretched necks).
• Common Ancestor – species from which two or more species have
diverged.
• Concerning Proteins: Species that share a recent common
ancestor (ex. Humans and gorillas) have few amino acid sequences
(order of amino acids to make proteins) where species that share a
common ancestor more distantly (ex. Humans and frogs) have
many amino acid sequence differences.
• Concerning Nucleic Acids: Scientists can directly estimate the # of
nucleotide changes that have happened since two species
diverged from a c. ancestor by comparing the exact nucleotide
sequence of genes. Using this, they can make a phylogenetic tree
to show how organisms are related through evolution (very strong
evidence)
Anatomy and Development Suggest
Common Ancestry
• Comparisons of the anatomy (structures) of different types of
organisms often reveal basic similarities in body structures, even
though their functions may be very different.
• Vestigial structures – some structures (like bones) are present in
an organism, but reduced in size and either have no use or have a
less important function (ex. Flightless wings on a cormorant or
the appendix on humans)
• As different vertebrates evolved,
particular sets of bones evolved
differently, but similar bone structure
can be seen. Homologous structures
are structures that share a common
ancestry – a similar structure in two
organisms can be found in their common
ancestor.
Does Evolution Occur in Spurts?
• The model of evolution in
which gradual change over a
long period of time leads to
species formation is called
gradualism.
• But Gould and Eldredge from
America hypothesize that
evolution occurs in spurts.
This model of evolution, in
which periods of rapid
change in species are
separated by periods of little
or no change, is called
punctuated equilibrium.
Section 13.3
EXAMPLES OF EVOLUTION
Industrial Melanism
• A well studied ex. Of natural selection in action is
industrial melanism, the darkening of populations of
organisms over time in response to industrial pollution.
• The best-known case involves the European peppered
moth, Biston betularia. Among the members of this
species, there are two color variations. Light and dark.
The dark was very rare until about the 1850s when
industrialization was occurring in major cities. 100
years later, almost all of the peppered moths near
industrial centers were dark.
How? Think…
Industry = factories
Factories = pollution or darkish grime
Grime covers tree trunks, so white moths get eaten and
dark moths survive. Survival of the fittest.
The Formation of New Species Begins with
Small Changes
• Species formation occurs in a series of stages.
Evolution continuously molds and shapes a
species to improve its “fit” to its environment.
• The accumulation of differences between
groups is called divergence.
• Within populations, divergence leads to the
formation of new species. Biologists call the
process by which new species form
speciation.
Forming Ecological Races
A species often lives in several
different kinds of environments.
If their environment is different
enough, local pops can become
very different.
Over time, populations of the
same species that differ
genetically because of
adaptations to different living
conditions become what
biologists call ecological races.
They are not different enough to
be different species, but they
may not be able to interbreed
successfully.
Maintaining a New Species
• Reproductive Isolation – inability of formerly
interbreeding groups to mate or produce fertile
offspring. Could be geographically isolated or may
reproduce at different times.