Transcript Chapter 10: Principles of Evolution

CHAPTER 10:
PRINCIPLES
OF
EVOLUTION
10.1 Early Ideas About Evolution
KEY CONCEPT
There were theories of biological
and geologic change before
Darwin.
Early Scientists Proposed Ideas About
Evolution
• Evolution is the process of biological
change by which descendants come
to differ from their ancestors.
• Four scientists laid the groundwork
upon which Darwin would build his
ideas
• Carolus Linnaeus, Georges Louis
Leclerc de Buffon, Erasmus Darwin,
and Jean-Baptiste Lamarck
Carolus Linnaeus
• Developed a classification system in the
1700s
• Based on similarities
• Proposed some organisms might have arisen
through hybridization
• Able to observe through experiments with
varieties of plants
Georges Leclerc de Buffon
• 1700s
• Proposed that species shared ancestors
instead of arising separately
• Rejected the common idea that Earth was
only 6000 years old
Erasmus Darwin
• Charles Darwin’s grandfather
• English doctor and poet
• Proposed all living things were descended
from a common ancestor and that more
complex life forms arose from less complex
forms
Jean-Baptiste Lamarck
• 1809
• Proposed that all organisms evolved toward
perfection and complexity
• Did not think species became extinct,
reasoned that they must have evolved into
different forms
Lamarck’s Theory
• Changes in an environment caused an
organism’s behavior to change, leading to
greater use or disuse of a structure or organ
• The structure would become larger or smaller as
a result
• The organism would pass on these changes to
their offspring
• Did not propose how traits were passed on to
offspring
• Explanation of how organisms evolved was
flawed
Inheritance of
acquired
characteristics
Example: giraffes neck
Theories of Geologic Change Set the
Stage for Darwin’s Theory
• There were three theories of geologic change.
– catastrophism
Age of the Earth
• Key issue in the early debates over evolution
• Common view was Earth was created about
6000 years earlier, and since that time
neither Earth or the species inhabiting it had
changed
• French zoologist Georges Culvier did not
think species could change but they could
become extinct, based on fossil evidence
Catastrophism
• States that natural disasters such as floods
and volcanic eruptions have happened often
during Earth’s long history
• These events shaped landforms and caused
species to become extinct
• Culvier argued that the appearance of new
species in each rock layer resulted from other
species moving into the area from elsewhere
Gradualism
• James Hutton (1700s) proposed that the
changes he observed in landforms resulted
from slow changes over a long period of time
• Argued the laying down of soil and creation
of canyons by rivers were not the result of
large-scale events, but from slow processes
• Idea become important to evolution and the
term gradualism is used to mean the gradual
change of a species through evolution
Uniformitarianism
• Charles Lyell wrote Principles of Geology published
in the 1830s
• Expanded the theory of gradualism into the theory
of uniformitarianism
• States that the geologic processes that shape Earth
are uniform through time
• Combines Hutton’s idea of gradual change over
time with Lyell’s observations of that such changes
have occurred at a constant rate and are ongoing
10.2 Darwin’s Observations
KEY CONCEPT
Darwin’s voyage provided insight
on evolution.
Darwin Observed Differences Among
Island Species
• Variation is a difference in a physical trait.
– Galápagos tortoises that live in areas with tall
plants have long necks and legs.
– Galápagos finches that live in areas with hardshelled nuts have strong beaks.
Adaptations
• An adaptations is a feature that allow an
organism to better survive in its
environment.
–Species are able to adapt to their
environment.
–Adaptations can lead to genetic
change in a population.
Darwin Observed Fossil and Geologic
Evidence Supporting an Ancient Earth
• Darwin found fossil evidence of species
changing over time
• Argentina: fossils of Glyptodon, giant
armadillo; resembled living species
• Darwin found fossil
shells high up in the
Andes mountains
• He saw land move
from underwater to
above sea level due
to an earthquake.
• Darwin extended
his observations
to the evolution
of organisms.
10.3 Theory of Natural Selection
KEY CONCEPT
Darwin proposed natural selection
as a mechanism for evolution.
Several Key Insights Led to Darwin’s
Idea for Natural Selection
• After voyage Darwin spent more than 20
years conducting research while thinking
about the way evolution occurs
• Work was influenced by observing farmers
and breeders
Artificial Selection
• Darwin noticed variation in domesticated
plants and animals
• The process by which humans change a
species by breeding it for certain traits
• Makes use of genetic variation by acting as
the selective agent
Darwin’s Pigeons
• Bred pigeons for hobby
• In order for artificial – or natural – selection
to occur a trait must be heritable
• Heritability: the ability of a trait to be passed
down from one generation to the next
• Breeders can select for or against specific
traits
neck feathers
crop
tail feathers
Natural Selection
• In nature the environment creates the
selective pressure that determines if a trait is
passed on or not
• A mechanism by which individuals that have
inherited beneficial adaptations produce
more offspring on average than do other
individuals
Thomas Malthus
• English economist
• Proposed that resources were natural limits
to population growth
• Human population would growth
geometrically if resources were unlimited
• Disease and limited food supply kept
population smaller
Struggle for Survival
• Darwin reasoned a similar struggle took place
in nature
• If resources are limited and organisms have
more offspring than could survive, those
well-suited for the environment would
survive
• Darwin proposed the adaptations arise over
many generations and called the process
“descent with modification”
Natural Selection Explains How
Evolution can Occur
• Alfred Wallace independently developed a
theory similar to Darwin’s theory
• Both presented their ideas to scientists in
1858
• A year later Darwin published On the Origin
of Species by Means of Natural Selection
4 Main Principles of Natural Selection
• Variation: basis of natural selection, differences
result from differences in genetic material
whether inherited of result of mutation
• Overproduction: results in competition
• Adaptation: certain variation allows an individual
to survive better, live longer, reproduce
• Descent with modification: increase in frequency
of the trait as long as the environment favors that
trait
Jaguar Example
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•
•
•
•
11,000 years ago many species faced extinction
Climate change caused food shortage
Fewer mammals; jaguars had to eat reptiles
Variation in jaw and tooth size in population
Jaguars with larger jaws and teeth could prey
more easily on shelled reptiles
• Descendants showed these modifications over
time
• Higher fitness
VARIATION
Natural Selection Acts on Existing
Variation
• Acts on phenotypes rather than genetic
material
• New alleles are not made by natural
selection
• Acts on traits that already exist
Changing Environments
• Ecologists Peter and Rosemary Grant: finches on
the Galapagos
• Drought caused reduced amount of small, soft
seeds but there was still plenty of large, toughshelled seeds
• Large-beaked finches were able to crack the
shells so they did not starve
• The following year there was an increase of
large-beaked finches and most of the smallbeaked finches died
Adaptations as Compromises
• Some structures take on new functions
• Paw of the panda: six digits; five that
resemble fingers and a small thumblike
structure
• “thumb” is actually an enlarged wrist bone
• Not considered a thumb because it does not
have separate bones and joints
• Not a wrist bone because it is longer than
needed to function for the wrist
10.4 Evidence of Evolution
KEY CONCEPT
Evidence of common ancestry
among species comes from many
sources.
Evidence for Evolution in Darwin’s Time
• Found evidence from a wide range of
sources
• Most convincing:
– Fossils
– Geography
– Embryology
– Anatomy
Fossils
• Age, location, environment when organism was
alive
• Fossils found in bottom layers of rock are older
than fossils found in upper layers of rock
• Geologists interested in fossil sequence as a
record of natural events such as earthquakes,
not as proof of evolution
• However fossil record supported Darwin’s
concept of descent with modification
Geography
• Island species most closely resemble
nearest mainland species
• Populations can show variation from one
island to another
• Important principle of biogeography (study
of the distribution of organisms around the
world
Embryology
• Noticed larvae of crabs and barnacles were
similar, both swim and look alike, Adult forms
act differently
• Vertebrates: all embryos have six pharyngeal
arches; upper arches become structures of the
face, ears, and jaws
• In fish the two lower arches become gills, in
humans fifth arch disappears and the third,
fourth, and sixth arches develop into the nerves,
bones, and other structures of the throat
Larva
Adult crab
Adult barnacle
Anatomy
• Homologous structures are similar in
structure but different in function
• Homologous structures are evidence of a
common ancestor
• Analogous structures have a similar function
• Analogous structures are not evidence of a
common ancestor
Vestigial Structures
• Unused or underdeveloped features
• Remnants of organs or structures that had a
function in early ancestors
• Pelvic bone of snakes
• Wings of ostrich
• Appendix of human
10.5 Evolutionary Biology Today
KEY CONCEPT
New technology is furthering our
understanding of evolution.
Fossils Provide a Record of Evolution
• Paleontology: the study of fossils or extinct
organisms
• Provides new information and support for
evolution
• Fossil record is not complete
• “missing links” : transitional forms,
demonstrate traits within groups as well as
the common ancestors between groups
Basilosaurus isis, found in Egypt,
has characteristics of both land and
marine animals
Molecular and Genetic Evidence Support
Fossil and Anatomical Evidence
• Very different species have similar molecular
and genetic mechanisms
• All living things share the same genetic code
and make most of the same proteins from
the same 20 amino acids
• DNA or protein sequence can be used to
show probable evolutionary relationships
between species
DNA Sequence Analysis
• The more related two organisms are the more
similar their DNA will be
Pseudogenes
• Sequences of DNA nucleotides
• No longer function but are still carried along
with functional DNA
• Functioning genes may be similar in
organisms with similar lifestyles
• Similarities between pseudogenes must
reflect a common ancestor
Homeobox Genes
• Control the development of specific
structures
• Found in many organisms from fruit flies
to humans
• Indicate a very distant common
ancestor
Protein Comparisons
• Similarities among cell types across
organisms can be revealed by comparing
their proteins
• Molecular fingerprinting
• A unique set of proteins are found in specific
types of cells
• Cells from different species that have the
same proteins most likely come from a
common ancestor
Eyespots of marine worm have lightsensitive cells with a molecular fingerprint
similar to that of a vertebrate eye
Evolution Unites All Fields of Biology
• Scientists are still studying evolution through
natural selection
• Natural selection combined with genetics is called
the modern synthesis of evolutionary theory
• Scientist from many fields contribute to the
understanding of evolution.
• The basic principles of evolution are used in many
scientific fields (idea of common descent helps
biologists understand where new diseases come
from, as well as, how to manage endangered
species)