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Evolution and Natural Selection Notes Packet
History of Life on Earth
Age of Earth is about 4.6 billion years old
Geological time periods are defined by changes in species through time and different species are found during
different time periods
How do we know the age of the Earth and fossils?
Geologists Hutton and Lyell argued that the earth is many millions of years old because
layers of rock take time to form and processes such as volcanoes and earthquakes shaped the earth and still
occur today.
Relative dating can determine a fossil’s relative age. Performed by estimating fossil age compared
with that of other fossils. Drawbacks – provides no info about age in years.
Absolute dating can determine the absolute age in numbers. Is performed by radioactive dating –
based on the amount of remaining radioactive isotopes remain, measured by the half-life. Drawbacks — part
of the fossil is destroyed during the test.
✴Evolution
“Nothing in biology makes sense except in the light of evolution.” ~Theodosius
Dobzhansky
Evolution is the single foundational theme of all of biology. It explains both the diversity AND unity of all life
on Earth…past, present, and future!
What is evolution?
Change over time. Change in heritable traits within a population through generations. Change in
allele frequency of a population through generations.
Evolution is just a theory…kind of like gravity!
Evolution is a scientific theory. A Scientific Theory is a very well supported explanation of a natural
phenomenon.
Charles Darwin (1809-1882) sailed around the world 1831-1836.
Darwin collected the preserved remains of ancient organisms - Fossils. Some of these fossils
resembled organisms that were still alive. Others looked unlike any creature ever seen
The Galapagos Islands: Each island had its own type of tortoises and birds that were clearly
different from other islands.
Why are they so different?
1. Large Ground Finch- Massive thick bill to crush large tough seeds
2. Medium Cactus/Ground Finch-bill used to cut into cactus for fruits, seeds, and insects. (also used
cactus spines as a tool)
3. Tree Finch- bills suited for buds, seeds and insects
4. Warbler finch- also live in trees but eat insects only.
5. Domed-shaped shell allows them to eat from plants located near the ground.
6. Intermediate shell allows them to eat both closer to the ground as well as higher up.
7. Sadle-backed shell allows them to eat higher up in a bush.
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What did Darwin’s travels reveal?
The diversity of living species was far greater than anyone had previously known! These observations
led him to develop the theory of evolution!!
How does evolution occur?
Mechanism of evolution: random changes and natural selection.
He stated that evolution has been taking place for millions of years, & continues in all living things
Darwin’s Theory
The theory of natural selection is composed of four principles or ideas/observations.
1. Variation exists among individuals within species.
2. Organisms produce more offspring than environment can support.
3. Competition exists among individuals.
4. Organisms with variations best fit to the environment are most likely to survive, reproduce, and pass
desirable variations to next generation. Produces change in heritable traits within a population across
generations.
✴Natural Selection
Process by which random changes are selected for by nature in a consistent, orderly, and non-random way.
The traits that help an organism survive in a particular environment are “selected” in natural selection.
Survival of the fittest. “Fittest” organisms survive to adulthood and reproduce. Requires variations of
inherited traits. Some more advantageous for survival & reproduction
Summary of Darwin’s theory:
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass those advantages to their children
5. Species alive today are descended with modifications from common ancestors
Why are variations important to understanding change in a population over time?
Because, variation is an inherited trait that makes an individual different from other members of its
species. These changes help them survive and are passed on to the next generation. Greater genetic
variability provides Greater adaptive potential.
✴Speciation
The evolutionary formation of new biological species, usually by the division of a single species into two or
more genetically distinct ones. In order for speciation to occur, FIRST the species needs to have inherited traits
or inherited differences.
Members of two populations become different and cannot interbreed to produce fertile offspring
✴Speed of Evolution
Gradualism
New species evolve from existing species through gradual, often imperceptible changes rather than through
abrupt, major changes. Small variations that fit an organism slightly better to its environment are selected for:
a few more individuals with more of the helpful trait survive, and a few more with less of the helpful trait die.
Gradually, leads to long time population changes.
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Punctuated Equilibrium
new species evolve suddenly over relatively short periods of time (a few hundred to a thousand years),
followed by longer periods in which little genetic change occurs. Change comes in spurts. Can be the result of
other causes, such as huge and sudden changes in the environment, like natural large scale disasters, that
result in more rapid changes in the organisms through harsher selection.
✴Evidence of Evolution
Fossil Record: provides evidence that living things have evolved. Fossils show the history of life on earth and
how different groups of organisms have changed over time.
Structural Similarities
Cells: basic unit of all life
Common cell structures: membrane with proteins; ribosomes
Homologous structures: Means the same type of structure. Showing a degree of similarity (e.g. in position,
structure, function or characteristics) that may indicate a common origin.
Vestigial structures: A structure in an organism that has lost all or most of its original function in the course of
evolution, such as human appendixes. Vestigial structures provide a clue to the evolutionary history of a
species because they are remnants of structures found in the ancestral species.
Developmental Similarities: Different species have similar embryonic stages which are features of
common ancestry.
Biochemical Similarities: all organisms share the Genetic code (DNA), Specific molecules (ATP,
Nucleotides, Amino acids), Cellular activities (Cellular respiration, Protein synthesis, DNA replication).
Comparison of DNA sequences, amino acid sequences/proteins, allows organisms to be grouped. This can tell
us which organisms are related.
✴Descent with Modification
Each living species has descended with changes from other species over time.
Branching Tree: a diagram that shows how scientists think different groups of organisms are related.
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