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History of Life (Ch. 25: History of Life on Earth (Fossil Record (types of…
History of Life
Ch. 25: History of Life on Earth
Conditions on Early Earth
macroevolution: broad pattern of evolution above species level
theory for how the first living cells appeared
1) small organic molecules made through abiotic (nonliving) synthesis
(1920's) A. I. Oparin and J. B. S. Haldane theorized that early oceans were full of simple molecs. that formed organic molecs. with the help of lightning or UV radiation
(1950's) Stanley Miller and Harold Urey testes Oparin-Haldane hypothesis and produced amino acids found in today's orgs.
small organic molecs. could have also formed from volcanic eruptions
they could have also formed in hydrothermal vents (areas on seafloor where hot water and minerals gush into ocean)
alkaline vents release warm water with a high pH, suitable environment for formation of organic molecs.
organic molecs. may have also formed from meteorites bc they could contain amino acids (that are rarely found on Earth), lipids, simple sugars, and nitrogenous bases
2) small organic molecs. formed macromolecs. like protein and nucleic acids
2009 study found that abiotic synthesis of RNA monomers could occur spontaneously from simple precursor
polymers of proteins and RNA can be produced if solutions of amino acids or RNA nucleotides are dripped onto hot sand, clay, or rock
3) protocells
protocells were vesicles filled with fluid and enclosed with membrane
could reproduce and metabolize simply
maintained internal chemical environment different from their surroundings
vesicles can form spontaneously when lipids are added to water; lipid bilayer similar to plasma membrane
protocells might have formed from lava bubbles on volcanic edges
4) self-replicating molecules
1st genetic material was RNA
ribozymes are RNA acting as enzymes to produce more RNA pieces
2013 Jack Szostak built a vesicle in which copying a template strand of RNA could occur
protocells with simple RNA would carry little genetic material which could be passed on by natural selection
Fossil Record
documents the history of life
types of fossils
fossils are found in sedimentary rocks bc of the layers of rock (strata) that settle on top of each other
the further down they are, the older they are
insects preserved in amber (fossilized tree sap)
mammals frozen in ice
why it is incomplete
many orgs. didn't die in the right place and time to be fossilized
many fossils haven't been discovered yet or have been destroyed by geologic processes
what orgs. were fossilized
species that existed for long time
abundant species
orgs. with hard hard shells, skeletons
how rocks and fossils are dated
radiometric dating: uses radioactive isotopes
as parent isotope decays into daughter isotope, rate of decay is specific for every isotope
half-lives: time required for 50% of parent isotope to decay
used to measure decay of radioactive isotopes
each radioactive isotope has a specific half-life
ex. Carbon-14 has quick half-life of 5,730 years
fossils contain isotopes that accumulated in orgs. while they were alive
carbon dating compares how much C-14 to C-12 (normal) in an org.
c-14 decays into nitrogen-14 starting at time of death
only works for fossils up to 75,000 years old bc fossils older than that have too little C-14
Key Events in Life's History
geologic record: standard time scale that divides Earth's history into 4 eons and further subdivisions
5 important eras
1) Archaean: 4,000-2,500 million years ago
oldest rocks on Earth's surface
oldest fossils of cells (prokaryotes in stromatolites)
atmospheric oxygen increases and most prokaryotes die
2) Proterozoic: 2,500-541 million years ago
oldest fossils of eukaryotic cells appear
diverse algae and soft-bodied invertebrate animals appear
3) Paleozoic: 541-252 million years ago
Cambrian explosion
marine algae; colonization of land by fungi, plants, and animals
bony fish; first tetrapods and insects appear
seed plants appear; origin of reptiles; amphibians dominant
4) Mesozoic: 252-66 million years ago
cone-bearing plants; dinosaurs evolve
flowering plants appear; most dinosaurs extinct and furry animals survive
5) Cenozoic: 66 million years ago-now
mammals, birds, pollinating insects
origins of primates
earliest human bidepal ancestors
origin of genus Homo
key events
First Single-Celled Orgs.
3.5 billion years ago, fossilized stromatolites (layered rocks formed when prokaryotes bound thin films of sediment together)
Photosynthesis and O2 Revolution
photosynthetic prokaryotes produced O2 (origins of cyanobacteria)
O2 revolution killed many prokaryotes while some anaerobic archaea survived in extreme environments
cellular respiration became an adaptation
1st Eukaryotes
1.8 billion years old, more complex than prokaryotes
endosymbiosis: prokaryotic cell engulfed aerobic cell that became a mitochondrion
mitochondrion developed before chloroplast (originated as a prokaryote that engulfed a photosynthetic cell)
Multicellularity
ex. orchestra can play variety of music while soloist can't
eukaryotic cells evolved into multicell. and having differentiation
small red algae 1.2 billion years ago
600 million years ago there were soft-bodied larger orgs.
Cambrian Explosion
535-525 million years ago many present-day phyla appear suddenly in fossils
sponges, cnidarians, molluscs
larger animals with predatory/defensive features
Colonization of Land
500 million years ago fungi, plants, animals began to colonize land
arthropods, tetrapods
human species originated 195,000 years ago
plants developed vascular system to absorb water through their roots and stay hydrated on land
Rise and Fall of Organisms
plate tectonics
spercontinents
i billion, 600 million, 250 million (Pangaea) years ago
continents are part of plates of Earth's crust that float on hot mantle (lava)
continental drift: movements in mantle cause plates to move over time
5 mass extinctions
in each, 50% or more marine species went extinct
happened bc of meteorites or volcanic eruptions that drastically changed climates
Permian Extinction
252 million years ago
killed 96% of marine species
lasted a few thousand years
volcanic eruptions in Siberia led to higher temps. and CO2 production which caused ocean acidification
Cretaceous Extinction
66 million years ago; killed all dinos
asteroid or comet collided with Earth and released debris that blocked sun for months, which decreased temp.
furry animals survived lower temps.
6th mass extinction
species are declining at an alarming rate
climate change is hastening decline of some species
human-caused extinction will happen in the next few centuries or millennia
consequences of mass extinctions
gets rid of many species and changes ecosystems
takes 5-10 million years for life to recover after an extinction
adaptive radiations
periods of evolutionary change in which groups of orgs. form new species with adaptations to allow them to live in new ecosystem after mass extinction
ex. furry animals survived the Cretaceous Mass Extinction
Changes in Body Form
effects of developmental genes
changes in rate and timing
heterochrony: evolutionary change in the rate or timing of developmental events
if puberty happens late, you might not grow to full genetic length
changes to these rates can alter adult form
paedomorphosis: reproductive organs mature faster than other body parts
ex. axolotls have juvenile bodies while their reproductive organs mature
these changes stay in genes as individs. reproduce and pass on traits to offspring
changes in spatial pattern
homeotic genes: master regulatory genes that determine basic features like where a pair of wings and legs will develop on a bird
a change to the loci of homeotic genes can cause body parts to grow in weird places
evolution in development
new genes are created by gene duplication events
new morphological forms can arise from changes in nucleotide sequences or regulation of developmental (new) genes
changes in gene sequence
new developmental genes (arising after gene duplication events)led to the origin of new body forms
changes in gene regulation
less harmful than changes in a gene's nucleotide sequence
Evolution isn't Goal Oriented
evolutionary novelties
as new species form, new and complex structures arise gradually
ex. eyes evolved in gradual increments
light sensitive photo-receptive cells
eyes evolved through series of steps that benefited the eyes' owners at every stage
evolution leads to
orgs. being better suited for their environments
shared characteristics of life
rich diversity of life
evolutionary trends
macroevolution produces patterns
as seen on a cladogram, all species develop new traits as time progresses
every step of cladogram includes a new trait
sometimes, species develop a trait that others do not, which creates branching in a cladogram
evolution is the result of interactions between orgs. and their current environments
this is why evolution doesn't have a particular goal
nor will it produce the "perfect" organism
as long as environment changes, new adaptations will appear bc natural selection tends to allow orgs. to be better adapted to their surroundings
Ch. 26: Phylogeny & Tree of Life
Phylogenies Show Evolutionary Relationships
evolutionary history of a species or group of species
ex. phylogeny of lizards and snakes indicates that glass lizard (legless) and snakes evolved from a distant common ancestor
analogous (convergent evolution) glass lizards and snakes evolved bc of similar environments, not from a recent common ancestor
systematics: constructs phylogenies by classifying orgs. and finding their evolutionary relationships
taxonomy: how orgs. are named and classified
hierarchy: DKPCOFGS
binomial nomenclature: scientific name given to orgs.
Genus species
if can't be italicized, then underlined
Carolus Linnaeus in 18th century
ex.
Homo sapiens
taxon: named taxonomic unit at any level like genus level
classification and phylogeny
phylogenetic tree: branching diagram that shows evolutionary history of group of orgs.
each branch point represents a common ancestor
sister taxa: groups of orgs. that share an immediate common ancestor that isn't shared by any other group (like chimps and humans)
all are rooted, which means that it includes the most recent common ancestor of all orgs. in the tree
basal taxon: lineage that diverges from all other members of its group early in history of that group
what trees don't show
show patterns of descent, not phenotypic similarity
don't show how old orgs. are or when they evolved
we shouldn't assume that a taxon evolved from a taxon next to it
lineage leading to humans and to chimpanzees both evolved from a recent common ancestor
just bc humans and chimps are together on a tree, it doesn't mean that they evolved from each other
this recent common ancestor isn't a chimp or a human, and now is extinct
Inferred Phylogenies
morphological and molecular homologies
homologies: phenotypic and genetic similarities due to shared ancestry
ex. similarity in number and arrangement of bones in forelimbs of mammals is bc they had a common ancestor with same bone structure
morphological homology
sorting homology from analogy
analogy: similarity between orgs. due to convergent evolution
occurs when similar environmental pressures and natural selection produce analogous adaptations in orgs. from diff. evolutionary lineages
analogous characteristics evolve independently
ex. African golden mole and Australian mole look alike but they differ in internal anatomy and reproductive systems
the more structures are similar in diff. orgs. the more likely it is that they evolved from same ancestor
ex. adult humans and chimps have skulls with bones fused together (structure is too similar to be a coincidence=they have a common ancestor)
orgs. with genes with many similar nucleotide portions=homology
evaluating molecular homologies
if 2 or more species are closely related, nucleotide sequences differ at only one or few sites
silversword plants share high similarity in their gene sequences even though they have many morphological diffs.
in distantly related species, nucleotide sequences have diff. bases or lengths bc insertions and deletions accumulate over long periods of time
Australian mole and African golden mole have very diff. DNA sequences, which means that their lineages have diverged substantially since their common ancestor
molecular homoplasy: coincidental matches in nucleotide sequences between distantly related orgs.
diff from homologous sequences, which resemble each other closely
ex. if 23% of nitrogenous bases are shared between distantly-related orgs.
matches in DNA doesn't necessarily mean that there's a relation between these orgs.
Phylogenetic Trees
cladistics: classification of orgs. based on common ancestry
clades: general groups that include ancestral species and all of its descendants
similar to Linnaean system
a taxon is only equivalent to a clade if it is monophyletic (consists of ancestral species and all of its descendants (single tribe))
paraphyletic (beside the tribe): consists of ancestral species and some of its descendants
polyphyletic (many tribes): includes distantly related species but not their most recent common ancestor
shared ancestral characters: originated in an ancestor of that taxon
ex. all mammals have backbones as well as their ancestors (all are vertebrates, such as reptiles and birds)
shared derived character: evolutionary novelty unique to a clade
ex. hair is shared by all mammals but not in their ancestors like birds and reptiles
inferring phylogenies using inferred characters
outgroup: a species from an evolutionary lineage that's closely related to but not part of the group of species that we are studying (ingroup)
used a basis for comparison
usually has one trait that other species in the cladogram do
ex. a lancelet would be the outgroup of a group of vertebrates (bc doesn't have a backbone, but is in Chordata) such as bass, frog, turtle, and leopard
phylogenetic trees with proportional branch lengths
some trees include the number of years (on a graph) to show how long a species has existed
phylogenetic trees as hypotheses
all trees are hypotheses about how orgs. fit together; nothing is 100% certain
best hypothesis is the one that best fits the available data
max parsimony and max likelihood
max parsimony: "Occam's Razor" the simplest explanation is the best explanation
can be applied to cladograms (the most simple ones are the best ones)
cladograms are speculations, so there can be many combinations of where the species go
maximum likelihood: cladogram created based on how DNA changes over time (ex. how DNA sequences change in related species over time)
computer programs use these principles to develop phylogenetic trees
Organism's Evolutionary History=Genome
gene duplications and gene families
diff. genes can evolve at diff. rates, even in same evolutionary lineage
rRNA (ribosomal RNA) changes slowly, so it's used to compare relationships between diff. taxa
ex. fungi are most related to animals than to plants
mitochondrial DNA changes rapidly, so it's used to study recent evolutionary changes
ex. Pima of Arizona, Maya of Mexico, and Yanomami of Venezuela are closely related by their mtDNA
gene families: groups of related genes in an orgs. genome
homologous genes: related by common ancestry; there will be lots of similar gene groups
orthologous genes: ancestral gene is found in two diff. species bc of a speciation event that occured in their evolutionary history
ex. gene that codes for a specific protein is found in both humans and dogs
can only diverge (change/mutate) after speciation has happened
paralogous genes: (parallel) happen within a species; gene duplicates and changes a bit within the same species
olfactory receptor genes have gone through several duplications in vertebrates (humans have 380 functional copies)
genome evolution
lineages that diverged a long time ago often share many orthologous genes
ex. human and mouse lineages diverged 65 million years ago, and 99% of their genes are orthologous
diseases in humans can sometimes be observed in other orgs. related to humans
Molecular Clocks
measures the evolutionary change in genes over the course of time
documented on a graph showing amount of mutations and number of years
in orthologous genes, # of mutations is related to time that has elapsed since the genes branched from their common ancestor
in paralogous genes, # of mutations is related to the time since the ancestral gene was duplicated in that same species
gives you an average rate of evolution
problems
assumes that mutations happen at the same gradual rate, but some genes change faster or slower over the course of time
same groups of genes may change at diff. rates in diff. species
neutral mutations are difficult to document on molecular clocks bc they may be unnoticeable in phenotypes of orgs.
harmful mutations might be quickly removed by natural selection without ever being documented on a molecular clock
some researchers try to extend molecular clocks beyond time span documented in fossil record of a particular gene
HIV in humans came from viruses that infect chimps and other primates
comparison of gene sequences show that HIV first spread to humans in 1930 or 1910
Tree of Life
from 2 kingdoms to 3 domains
at first scientists classified orgs. into 2 kingdoms: plants and animals
5 kingdoms were thought of in 1960's: Monera (Protists), Protista, Plantae, Fungi, Animalia
Monera was split into two groups: Archaea and Bacteria (domains)
now there's 4 kingdoms in Eukarya (all have true nuclei and membrane-bound organelles)
Protista
only Eukaryotes that are unicellular and encompass broad types of orgs. that are most like the other kingdoms in Eukarya like mold, algae, and plankton
Fungi
Plantae
Animalia
2 cell types: Prokaryotes and Eukaryotes
3 domains: Archaea, Bacteria, and Eukarya
horizontal gene transfer
1st major split in history of life occurred when bacteria diverged from other orgs.
this is why archaea are closer to eukarya than to bacteria
h. gene transfer: genes pass from one genome to another through exchange of transposons and plasmids, viral infection, and endosymbiosisi
ex. 80% of genes had moved between 181 prokaryotes
there has been h. gene transfer between all 3 domains
in eukaryotes, can happen through viral infections such as HIV and herpes where the virus DNA changes human DNA to the point where it stays changed forever
in prokarotes, can happen through transformation or conjugation