Download Chapter 7: Evolution

Chapter 6: Change Over Time
Charles Darwin – The Origin of Species
Darwin’s Theory
Key Vocabulary & Concepts
A trait is a characteristic that an organism passes
to offspring through its genes.
Sexual reproduction results in offspring that are
genetically different from each parent.
DNA is genetic material that carries information
about an organism and is passed from parent to
offspring.
A (scientific)theory is a well-tested concept that
explains a wide range of observations.
An adaptation is a trait that helps an individual
survive and reproduce.
A species is a group of similar organisms that can
mate with each other and produce fertile offspring.
A fossil is the preserved remains (solidified/imprints) or
traces of an organism that lived in the past.
The process of change over time is called evolution.
In artificial selection, only the organisms with a desired
characteristic, such as color, are bred. (Human controlled)
What was Darwin’s hypothesis?
**Natural selection is the process by which individuals that
are better adapted to their environment are more likely to
survive and reproduce more than other members of the
same species.
Factors that affect the process of natural selection:
overproduction, variation, & competition
Any difference between individuals of the same species is
called a variation.
What is natural selection?
**Darwin proposed that over a long time, natural selection
can lead to change. Helpful variations may accumulate in a
species, while unfavorable ones may disappear.
Evidence of Evolution
What evidence supports evolution?
**Fossils, patterns of early development, similar body
structures, and similarities in DNA and protein
structures all provide evidence that organisms have
changed over time.
FOSSILS
The Earth’s crust is arranged in layers of different
types of rock. Older layers are deposited before
newer layers and are therefore deeper in the crust.
Fossils are found in the rock layers. They provide a
historical sequence of life called the fossil
record(ex. Fossils found in the upper layers tend to
resemble present day organisms, deeper layer fossils
tend to look quite different)
Gaps remain in the fossil record because:
•fossils only form under certain conditions (must be
free of oxygen)
•not all organisms form fossils
•scientist haven’t excavated all the rock on Earth
PATTERNS OF EARLY DEVELOPMENT
Embryonic Structure: early embryos are
nearly indistinguishable among major
groups such as vertebrates
SIMILAR BODY STRUCTURES
Homologous Structures : bones in differing
species are often found in the same amount and
position. These bones have been modified over
time for different purposes.
Organisms that have similar body structures
share a common ancestor.
Vestigial Structures: Remnants of once useful
structures that no longer have a purpose (ex.
Whales have hind-limb bones in their bodies)
SIMILARITIES IN DNA & PROTEIN
STRUCTURES
Genes are segments of DNA. New genetic
studies allow for DNA comparison. The
more similar the DNA sequences, the more
closely related the species are. If
organisms have evolved from a common
ancestor, they must share much of their
genetic information which has shown to be
the case.
Section of Cytochrome c Protein in
Animals
The table shows the sequence of amino acids in one
region of a protein, cytochrome c, for five different
animals. Each letter corresponds to a different amino
acid in the protein.
In most cases, evidence from DNA and
protein structure has confirmed conclusions
based on fossils, embryos, and body
structure.
Rate of Change
How do new species form?
Natural selection explains how variations can lead to changes in a
species, but how could an entirely new species form?
A new species can form when a group of
individuals remains isolated from the rest of its
species long enough to evolve different traits
that prevent reproduction.
What patterns describe the rate of evolution?
Scientists have developed two patterns to describe
the pace of evolution.
Gradualism: small changes that add up to major changes
over a long period of time (slowly and steadily)
Punctuated Equilibrium: species evolve during
short periods of rapid change (quickly over short periods of
time)