Biology Chapter 10 Notes: The Origin and
Diversification Of Life on Earth
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how did life on earth begin? Life is defined by the ability to replicate and by the presence of
some sort of metabolic activity
Earth formed about 4.5 billion years ago from clouds of dust and gases left over after the
formation of the sun; initially super-hot and gradually cooled; first life on earth tolerated an
atmosphere without oxygen; atmosphere originally had a large amount of carbon dioxide,
nitrogen, methane, ammonia, hydrogen and hydrogen sulfide "Darwin's warm little pond"
Biodiversity: variety and variability among all genes, species and ecosystems on the planet
Multiple suggestions on the start of the first organisms; classified by several distinct phases
instead
Phase 1: formation of small molecules containing carbon and hydrogen; no oxygen was original present
in old rocks; because of the chemical structures, the molecules bond very easily and in many ways;
caused them to have huge variety of forms and functions
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Stanley Miller and Harold Urey created an environment for the "warm little pond"
A flask of water with H2, CH4 (methane) and NH3 (ammonia); they subjected their mini-world to
sparks, to simulate lightning; they cooled the atmosphere so that any compounds formed in it
would rain back down into the water; they waited and examined the contents of the water and
to see what happened; discovered many organic molecules including 20 different amino acids;
promising steps but the ozone in the atmosphere would not have had protection against UV
rays that broke down methane and ammonia
Phase 2: the formation of self-replicating, information containing molecules; researchers have
discovered a molecule that could function as an enzyme that links together nucleic acids (nucleic acid
RNA); notable because it means that the single relatively simple molecule could have been selfreplicating; supports RNA world hypothesis which proposes that the world may have been filled with
RNA-based life before it had DNA-based life; 3.4 billion year old cells have been found in rocks from
South Africa; life is typically determined by two characteristics; the ability to replicate and the ability to
carry out some sort of metabolism; RNA molecules satisfied the replication but not the metabolism
Phase 3: the development of a membrane, enabling metabolism and creating the first cells; membranes
make numerous aspects of metabolism possible; they make it possible for chemicals inside the cell to be
at higher concentrations than if they were outside the cell which are essential to most life-supporting
reactions; suggestions that the first cells may have come together spontaneously; mixtures of
phospholipids placed in water/salt solutions tend to spontaneously form small spherical units that
resemble living cells; these spontaneous membranes might have formed around a self-replicating
molecule creating these microspheres
Species & Biodiversity
Biological Species: populations of organisms that interbreed or could possibly interbreed with each
other under natural conditions and cannot interbreed with organisms outside their own group; instead
of physical features, the emphasis goes towards reproductive isolation; just because the individuals are
physically separated, they aren't necessarily in different species (could possibly interbreed); conditions
are not considered natural when under captivity
Prezygotic Barriers: makes it impossible for individuals to mate with each other or for the male's
reproductive cell to fertilize the female's reproductive cell; includes situations in which the members of
the two species have different courtship rituals or physical differences or biochemical factors
Postzygotic Barriers: occurs after fertilization and generally prevent the production of fertile offspring
from individuals of the two species; such offspring are called hybrids; either do not survive long or
survive and are infertile or have reduced fertility; mules are a hybrid of horses and donkeys and cannot
breed with each other or produce offspring
Naming Species
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important for biologists to order and classify life; uses the system developed by Swedish
biologist Carolus Linnaeus in the mid 1700s "Systema Naturae" or "System of Nature"
every species is given a scientific name that consists of two parts; a genus and a specific epithet;
Homo-sapiens are humans; the "species" is the narrowest classification for an organism
Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species
plants and animals are referred to by common names but also have their official names in the
Linnaen system
Not Always Easily Defined
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can be biased towards the classifications and decisions
Difficulties classifying asexual species; asexual reproduction does not involve interpreeding, the
concept of reproductive isolation is no longer meaningful; might seem that every individual
should be considered a separate species
Difficulties classifying fossil species; differences in size and shape of fossil bones cannot reveal
whether there was reproductive isolation between the individuals from whom the bones came
Difficulties in determining when one species has changed into another; unsure about what exact
point did the certain species turn into another
Difficulties in classifying ring species: two non-interbreeding populations may be connected to
each other by gene flow so there is no exact point where one species stops and the other
begins; gradual changes in reproductive isolation accumulate so when the populations meet up
again, there are sufficient differences physically and behaviourally; green warblers are one of
the 20 examples of ring species
Difficulties in classifying hybridizing species: the interbreeding of closely related species;
sometimes occurs and produces fertile offspring suggesting that the borders between the
species are not clear cut; morphological species concept characterizes species based on physical
features such as body size and shape (subjective but can be effectively used to classify some
asexual species); does not require the knowledge of whether individuals can actually interbreed
How Do New Species Arise?
Speciation: the process in which one species splits into two distinct species; occurs in two phases and
requires more than just evolutionary change in a population
1. Reproductive isolation: through which two populations come to have independent evolutionary
fates
2. Genetic divergence: two populations evolving as separate entities accumulate physical and
behavioural differences over time as they become adapted different to features of their
separate environments including different predators, types and abundances of food available
 Allopatric speciation: Speciation with geographic isolation; over time, the two split populations
have different evolutionary paths as they adapt to particular features of their habitats; two
populations eventually may genetically diverge enough that if the two species interact again,
they might not be able to interbreed; Galapagos Island finches; might be separated through
rivers, glaciers or landforms resulting into different environments
 Sympatric speciation: speciation without geographic isolation; can also occur among populations
that overlap geographically; rare in animal populations but is common among plants; during
plant cell division, an error sometimes occurs in which the chromosomes are duplicated but the
cell does not divide; doubling of number of sets of chromosomes is called polyploidy; these
plants can no longer interbreed with each other but can propagate through self-fertilizations or
by mating with other individuals that have the same sets of chromosomes; more common
method occurs when plants from different but closely related species interbreed forming
hybrids; propagates itself asexually; can ultimately produce fertile individuals ; process of
speciation called allopolyploidy
 when reproductive separation occurs, new populations are isolated from each other but could
potentially still interbreed; speciation is not complete until sufficient differences have evolved in
the two populations and they can no longer interbreed even if they do come in contact;
speciation can be difficult to observe and study because of the time it sometimes might take
Conceptual Evolutionary Trees
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Phylogeny: evolutionary history of organisms; all species are named and arranged in a manner
that indicates the common ancestors they share and the points at which they diverged from
each other; the divergence points are called nodes
A Phylogenetic tree not only shows the relationships among organisms but also presents a
hypothesis about the evolutionary history of species; unfolding story; speciation events are
included; are hypotheses and subject to revision; uses data from DNA sequences and molecular
evidences instead of physical features previously used
Bacteria > Archaea > Eukarya---> Prosists > Plants > Fungi > Animals
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monophyletic: describes a group in which all of the individuals are more closely related to each
other than to any individuals outside that group; animals would be closer to fungi in comparison
to plants
DNA-Based Evolutionary Trees: compares similar DNA sequences that are between two groups;
possible to estimate how long it has been since two species shared a common ancestor
Before DNA-Base evolutionary trees, physical features were used; similar structures aren't
always what they seem and can be deceiving; Bats did not inherit wings from insects, instead,
wings are an adaptation that arose separately on more than one occasion
Convergent evolution: occurs when populations of organisms live in similar environments and so
experience similar selective forces possible explanation as to why some organisms look the
same
Analogous traits: characteristics that are the same because they were produced by convergent
evolution and not because they descended from a common structure in a shared ancestor
(wings)
Homologous features: features that are inherited from a common ancestor; reptiles and mouths
DNA analysis helps determine whether the trait is homologous or analogous; molecular
phylogenies cannot be fooled under this method
Macroevolution
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Macroevolution: large-scale examples; products of evolutionary change involving the origins of
entirely new groups of organisms; above the evolution of species level
microevolution is the phenomena involving changes in allele frequencies in a population
similar processes; evolution is a change in allele frequencies over time; accumulated effects of
this process over a long period of time can lead to the dramatic phenomena of macroevolution
pace of evolution is not constant; evolution by creeps represent populations changed slowly but
surely, gradually accumulating sufficient genetic differences for speciation; evolution by jerks
represent populations that undergo brief periods of rapid evolutionary change immediately
after speciation followed by long periods with relatively little change
Punctuated equilibrium: rapid periods of evolutionary change are punctuated by longer periods
with little change; opposes a problem for evolutionary biology; it is mistakenly believed that the
rapid evolutionary changes of punctuated equilibrium are the result of some new mechanism of
evolution but in actually, per-generation rates of change necessary to produce it are relatively
slow and not at all beyond the rates of change that have been measured in evolving
populations; existence of "gaps" in fossil record seems to imply that the transitional species did
not exist but the population experiences the most extreme selective pressures and the organism
becoming a fossil has a very low chance of existing
evolution consists of different rates across all species
Adaptive Radiation
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in a brief period of time in which a small number of species diversified into a much larger
number of species; able to live in a wide diversity of habitats; such a large and rapid
diversification has occurred many times throughout history
1. Mass extinction events: large-scale extinctions
2. Colonization events: one or a few birds or small insects will fly off from a mainland and end up
on a distant island group (Hawaii, Galapagos); tend to find a large number of opportunities for
adaptation and diversification
3. Evolutionary Innovations: "killer app" that immediately leads to a huge success; rigid outer
skeletons, flowering plants
Extinctions
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Extinction: complete loss of all individuals in a species population
Background extinction: describes the extinction that occur at lower rates during periods other
than periods of mass extinction; occur mostly as a result of natural selection; species might be
too slow to adapt to gradually changing environmental conditions
Mass extinctions: periods during which a large number of species on earth become extinct over
a relatively short period of time; at least 5 mass extinctions that resulted into the extinction of
50% or more of animal species living at the time
An Overview of Diversity
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all organisms are classified into one of three groups; originally it was plants, animals and mineral
kingdoms; with the technology of discovering microscopic organisms, there are now new
Domains; Bacteria, Archaea & Eukarya
Carl Woese began to examine organisms and classfying them according to nucleotide
sequences; discovered a perfect candidate for the role (RNA)
horizontal gene transfer: rather than passing genes simply from parent to offspring, they transfer
genetic material directly into another species; problematic in bacteria
Viruses: might be a fourth group; not classified as living because they take hostage upon other host
organisms
1. Bacteria arose from the first self-replicating metabolizing cells
2. There was a split between the bacteria and a line that gave rise to the archaea and eukarya
3. The fusion of bacterium and an archaean gave rise to the eukarya, which then split from the
archaea line
Bacteria
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has tremendous biological diversity; single-celled organisms with no nucleus or organelles; one
or more circular molecules of DNA
thrives on your tongue and in your mouth; hundreds of species in a teaspoon of soil; asexual and
reproduces by fission; some are good bacteria while some are bad
Archaea
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thrives in the most inhospitable seeming places; began diverging about 3 billion years ago;
eukarya split off from the archaea about 2.5 billion years ago; single celled prokaryotes
have cell membranes, ribosomes and some enzymes similar to those found in the eukarya
Five Main Groups:
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2.
3.
4.
Thermophiles (heat lovers): live in very hot places
Halophiles (salt lovers): live in very salty places
High and Low pH tolerant archaea
High pressure tolerant archaea: found as deep as 4,000 meters below the ocean surface where
the pressure is almost 6,000 pounds per square inch
5. Methanogens: anaerobic, methane-producing archaea
Eukarya
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consists of four kingdoms: plants, animals, fungi, and prosists
all made up from eukaryotic cells; membrane-enclosed nucleus; each kingdom is almost entirely
multicellular
Prosista: often invisible to naked eye; sort of grab bag that includes a wide range of mostly
single-celled eukaryotic organisms; amoebas, paramecia, algae; discovery of prosists continues
at a very high rate; likely to be most diverse kingdom within eukarya
eukarya split from archaea about 2.5 billion years ago; at that time eukarya probably resembled
modern prosists that more than any other modern eukarya
the split may have occurred when symbiotic bacteria became incorporated within an ancestor of
the eukaryotes resulting in what would become mitochondria
1.5 billion years ago, a second important symbiosis between bacteria and eukarya resulted in
chloroplasts
much easier to see than bacteria and archaea, there is a disproportionate number of named
species on earth compared within the domains
majority of the 1.5 million named species are eukarya with about half being insects; result of the
interests and biases of biologists than a reflection of the relative numbers