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Chapter 15: The Origin of Life
Abiogenesis: spontaneous generation; was generally believed as
the way that new life formed...
...when actually BIOGENESIS was proven using the scientific method
by (among others)
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Francesco REDI- (17th century) "Does life really arise from
rotting meat?"
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Louis PASTEUR- (19th century) "Does life arise from materials
in the air?"
Biogenesis shows that life comes from pre-existing life, but does NOT
explain where the first life came from. What is the Origin of Life on
Earth???
There are Many Theories...
Some of the thoughts:

Special Creation ("God")

Extraterrestrial Origins, or "Panspermia" (life came from
OUTER SPACE). Evidence of organic compounds HAS been
found in recovered meteorites.
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Chemosynthesis (chemical reactions occurred here on the
young earth that resulted in organic compounds forming and
then cells from these). This is by far the most popular scientific
theory and probably the best-supported.
One of the strongest hypotheses is "Chemosynthesis", or chemical
evolution of the first cells on the planet earth, put forth by Alexander
Oparin (early 1900's)
Young earth --->
(1) volatile atmospheric gases (H2, H2O, CH4, NH3...) (NO O2),
(2) warm seas,
(3) energy from volcanoes, lightening, UV
1+2+3= MAYBE the first organic compounds formed as a result of this
chemical reaction, much like in a test tube! When the seas washed
onto shore and the puddles evaporated, the organic molecules were
condensed into "packets" which were able to sustain themselves;
"cells"
This idea was NOT popular in the scientific community; it sounds an
awful lot like spontaneous generation! Until...
...the experiment was tried out in a lab by Stanley Miller and Harold
Urey (1953) who were NOT able to make cells, but did manage to
cook up some organic molecules necessary for cells (amino acids,
nucleotides, ATP)
(Since then, modification of this experiment have been explored and
some labs (See Sydney Fox) have been able to come up with some
self-sustaining cell-like things (protocells, coacervates,
microspheres)...who knows? If given a billion years or so...???)
Formation of Earth:
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*
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Solar system estimated to be approximately 5 byo
-This swirling mass of gas/dust collapsed inward (=sun)
-Planets formed from violent collisions of space debris
Estimated Age of earth about 4.6+ byo
1st life forms found to be ~3.5+ byo, primitive prokaryotic cells
Scientific Evidence (Dating Methods):
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The lineage of organisms (fossils) can be traced down through
layers of rock of different ages (Lowest = Oldest).
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Radiometric analysis: ages can be determined using elements
in the rock- radioactive isotopes like 14C, 40K, 238U.
-Radioactive isotopes have unstable nuclei that break
down, give off radiation, and form new elements
-Ex:
C  12C (1/2 life is 5730 years)
40
K  40Ar (1/2 life is 1.3 billion years)
14
Living organism: Mollusk is absorbing 12C and 14C
from the environment. The Ratio of 14C and 12C is the
same.
Dead organism: Once the mollusk dies, it no longer
absorbs carbon. The radioactive 14C begins to decay
and the amount of 14C in the mollusk shell decreases,
while the amount of 12C remains the same.
History: Because half of the 14C decays every 5730
years, the mollusk fossil's age can be determined by
finding the ratio of 14C to 12C in the fossil and
comparing it with the ratio in living organisms.
-Ex: It is determined that a fossil contains of 98 grams of
12
C. The amount of 14C is determined to be 6.125 grams.
How old is the sample?
First, determine how many times the sample was
reduced by 1/2:
98/2 = 49
49/2 = 24.5
24.5/2 = 12.25
12.25/2 = 6.125
= 4 half lives
Second, look up the half-life of 14C (5730).
Third, multiply the half-life by the number of half-lives
that you calculated to have occurred.
5730 x 4 = 22,920
From Molecules to Cell-like structures:
Sydney Fox – studies formation of 1st cells

Microspheres: spherical & composed of protein molecules

Coacervated: collection of droplets that are composed of
molecules of nucleic acids and sugars
-These can spontaneously form under certain conditions
-Indicated that important aspects of cellular life can arise w/out
direction from genes (ex. RNA can act as an enzyme)
1st life form -> prokaryotes: unicellular, simple, anaerobic, heterotrophic
competition ensued...
---> chemotrophic autotrophs, unicellular, simple, anaerobic
(Archaebacteria)
---> photosynthetic autotrophs, unicellular, simple, anaerobic
brought about changes on earth...helped to add oxygen to the air...
...atmosphere forming, cloud cover, ozone (protection)
---> first eukaryotes...unicellular, about 1.5 bya; membrane-bound
nucleus and organelles..."endosymbiont hypothesis"
-->first multicellular organisms about 750 million yrs ago (fossils) fairly "recent"!
Chapter 16: Evolution
Early Evolutionary Theory
Evolution (the theory that living things have changed over the earth’s
history) is NOT a new idea.
One of the earliest systematic theories was that of Jean Baptiste de
Lamarck. He proposed that organisms developed or lost features
due to "use or disuse". This was called the Inheritance of Acquired
Characteristics (1809). For example: if a giraffe stretches its neck
to reach higher branches in trees, will its offspring have longer necks
as a result?
Charles Darwin
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as a young man, Englishman Charles Darwin served as a
naturalist on the British naval vessel the HMS Beagle
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he observed and collected specimens and fossils through parts
on S. America and the S. Pacific (1831-36)
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he read books on 1: geologic time (Sir Charles Lyell) and was
aware that landforms and habitats change over time and that the
earth was very old 2: populations (Thomas Malthus) which proposed
that populations do not grow unchecked. There is limited space, food,
& resources so there is a struggle for existence.
The Galapagos Islands- off the coast of Ecuador; relatively "young"
islands, formed largely from volcanic activity. They became inhabited
with organisms from the mainland, but Darwin observed that each
organism had evolved different features to adapt to the different island
habitats until they had become separate, yet similar species.
examples: 13 different species of finches, 14 different species of
tortoises, etc.
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Darwin returned to England to think about it for a while.
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Many years later, he published his theory of evolution in a book
called "...On the Origin of Species" (1859)
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It should be noted that others, like Alfred Russel Wallace, had
come up with this idea as well, but were as reluctant as Darwin to
publish due to the political and religious themes of the day.
Darwin realized that the earth is VERY old and has a long history of
changes. This allows for:
1. VARIATION: Variation is the raw material for natural selection.
Genetic (allele) variation is good! An inherited variation that increases
an organism's chance of survival in a particular environment = an
"adaptation". Adaptations that suit an organism in one environment
may not be advantageous in another; and environment and habitats
change, so must the organisms- - -> this may lead to new species
over time.
2. COMPETITION: Living things face a constant struggle for
existence. Predators, food, water are all limited. More organisms are
born than can survive = competition; this sets up the so-called
"survival of the fittest".
3. SELECTION: Organisms with that survive (and have favorable
variations) will reproduce at a higher rate = "natural selection". This
carries over their genes to another generation. Over successive
generations, this tends to make a population better suited to its
environment.
Those are the three main points in his book.
Patterns of Evolution
1. Divergent evolution: when isolated populations of a species
evolve independently (ex: red fox/kit fox or even dogs)
-usually occurs when geographic barriers separate
members of a population
-also occurs when a small group leaves an original
population to colonize a new area
-Adaptive Radiation: the evolution of many diversely
adapted species from one common ancestor
-Example: Darwin’s Finches  Each species
evolved from the original ancestor but as they traveled
to different islands they had to adapt to the
surroundings.
2. Convergent Evolution: unrelated species become more and
more similar in features due to adaptation to similar environments (ex:
cacti/euphorbs)
3. Coevolution: the joint change in two or more species in close
interactions. As one changes, it forces the other to adapt to it. ex:
flowers/ pollinators
Evidence for Evolution
There is quite a bit of scientific evidence that things began as simple
cells and later changed into a variety of complex organisms which,
have themselves changed over time. Some new species develop
while others become extinct, but all can be traced back to a common
ancestor.
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Evolution is the theory that new species form when populations
break off and develop traits that are different (new species). We can
be traced back to a common ancestor.
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Species change largely due to random changes (mutations) in
their genes that occurs over a period of time.
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In general, genetic changes that translate into some type of
physical trait which give an organism an advantage are passed on to
future generations, while those genes that put an organism at a
disadvantage will probably not survive.
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Which traits are favored, of course, depends upon the
environment in which a species lives.
Evidence from Fossils:
The lineage of organisms can be traced down through layers of rock
of different ages. Organisms leave behind FOSSILS or molds, casts
or imprints in various strata of the earth.
Ages can be determined using elements in the rock- radioactive
isotopes like 14C, 40K, 238U
Evidence from Living Organisms:
1. Similar Physical features = Common Ancestry: It LOOKS like
several "new" species may evolve from one original species, mainly
because of geographic separation (called allopatric speciation).
example: Hawaiian Honeycreepers- birds that are different enough to
have become separate species but have marked physiological
similarities to one another. This would suggest they all started out as
the same species, but diverged over time as they adapted to different
islands.
2. Homologous Structures: Why do a bird wing, a human arm, a
dog foreleg and even a whale's flipper all have the same bones in
them? They all have different uses, but the same underlying
physiology (radius, ulna, humerus, phalanges, etc.). This could mean
that they evolved from the same common ancestor. Refer to Fig. 15-7
on pg. 289 of the text.
3. Vestigial Organs: Why do we have structures that we seem to
have no use for? Like a tail bone (coccyx)? Our appendix? Ear
muscles? Even whales have finger bones in their flippers. Some
snakes have pelvic bones, but no legs attached? What's behind
these??? MAYBE these "left-overs" point to our relationship to
organisms that actually use these structures.
4. Embryological Development: Related organisms tend to have
embryos that resemble one another and develop similarly. Refer to
Fig. 15-9 on pg. 291 of the text.
5. Molecular Biochemistry: Analyses of the amino acid sequences
or DNA of some organisms reveals similarities or differences between
them. These can be utilized to determine relatedness.
Chapter 17: Evolution and Speciation
A "species" is a group of like organisms that are capable of
reproducing viable offspring in nature.
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Morphological species: based on similarities/differences in
structure; easy to observe
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Biological species: can interbreed
Variation of Traits in a Population
Population: all the members of the same species that live in a
particular location at the same time and have the potential to
interbreed.
Members of a population, even though of the same species, are
somewhat different genetically.
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*
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mutations in DNA
recombination of genes during meiosis
random fusion of gametes
A difference in genotype usually results in a difference in phenotype
Often, variation in traits are due also to environmental factors as well
Example: Why are some of the perch in a pond bigger/longer than
others?
Bell Curve:
Allele Frequencies and Genetic Equilibrium: Population Genetics
Variations in genotype arise through mutation, recombination and
crossing-over
Gene Pool: the collection of genes for all the traits in a population
(contains all the alleles for all the genes)
Allele Frequency: the percentage of a specific allele of a gene in the
gene pool
A population in which allele frequencies do not change from one
generation to the next is said to be in Genetic Equilibrium
To maintain genetic equilibrium, several conditions must be met:
-no mutations
-no migrations
-large populations
-random mating
-no selection of alleles (no natural selection)
DISRUPTION OF GENETIC EQUILIBRIUM
When gene frequencies change over time (Hardy-Weinberg does
NOT hold true) then EVOLUTION happens.
Factors that cause change in gene pools:
1. Mutation
2. Migration
3. Genetic Drift: allele frequencies in a population change as a result
of random events or chance
4. Natural Selection: some alleles are more favorable to have than
others
TYPES OF NATURAL SELECTION
Stabilizing Selection: selection that favors the most common variation
Directional Selection: a shift in the bell curve one way or the other
Disruptive Selection: selection that does not favor the most
common variation of the trait w/in the poplulation
Sexual Selection: mate preferences based on traits, usually some
physical feature
FORMATION OF SPECIES
Speciation: the evolution of one or more species from a single
ancestor species
-when a species has been geographically separated and
over time no longer can reproduce
Ch. 18: Classification of Living Organisms (Taxonomy)
Taxonomy: the science of classifying or grouping organisms; based
on their presumed natural relationship
An estimated 10 million organisms live on the planet (only a small
fraction of the number that have ever existed in the earth's history) but
only around 10% have been classified
Why classify?
1. organization for study purposes
2. common names may be misleading (ex: starfish, jellyfish,
goldfish)
3. scientists need a universal naming system (like metrics)
4. shows relationships between organisms (evolutionary path)
One of the earliest taxonomic systems was set up by Aristotle
around 2,000 yrs ago, based on his limited observations of
organisms. He divided creatures up into 2 groups (plants/animals).
Carolus Linnaeus- a Swedish naturalist who set up a system of
grouping organisms into hierarchal categories, outlined in his
Systema Natura; gave everything Latin names for:
NOTE: "Phylum" is often called "Division" in botany (plants)!
“Species” is called a “Strain” in monera (bacteria)!
WITHIN a species, there may also be BREEDS, RACES, or
VARIETIES that show distinctive phenotypes.
We still use this system today, based on objective observations of
structure, habitat, ancestry, etc.
These classification categories are still used, but modern taxonomists
have added to and amended it somewhat now that we have
technology that can show biochemical and genetic similarities =
more quantitative evidence as to degree of relatedness.
We can also divide Linnaeus’s categories even further, if needed:
subspecies, superclass, supphylum, etc.
Today, every living thing has a universal Latin name, known as
binomial nomenclature (2-part name) genus, species.
"Making Order out of Chaos"
Systematics: organizes the tremendous diversity of living things in
the context of evolution; kind of a "who's related to whom" system.
Phylogenetic tree: is a family tree showing the evolutionary
relationships thought to exist among groups of organisms (for
example, see pg. 343, Fig. 18-3).
Evidence used to classify organisms into such groupings:
1.
2.
3.
4.
fossil records
morphology (structure/forms in organisms)
embryological patterns of development
chromosomes and macromolecules
Cladistics: a relatively new system of phylogenetic classification,
using certain features of organisms called "shared derived
characteristics" to establish relatedness. Cladogram (for example, see
pg. 346, Fig. 18-6).
THE SIX KINGDOM SYSTEM
Kingdom
Archaebacteria
Eubacteria
Protista
Fungi
Plantae
Animalia
Cell type
prokaryotic
prokaryotic
eukaryotic
eukaryotic
eukaryotic
eukaryotic
Number of Cells
unicellular
unicellular
mostly unicellular
mostly multicellular
multicellular
multicellular
Nutrition
both (auto & heterotrophic)
both
both
heterotrophic
autotrophic
heterotrophic