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chapter 25 macroevolutionary history of life on earth (key events in…
chapter 25
macroevolutionary history of life on earth
key events in "life's history"
early multicellular eukaryotes
1.2 billion years ago -oldest fossils of multicellular organisms -small red algae
.6 billion years ago -more diversity, ediacaran biota
eukaryotes
1.8 billion years ago -oldest fossils of eukaryotic cells
supposed to have evolved by infolding of the plasma membrane for ER and other organelles
and endosymbiosis for mitochondria and plastids
evidence for endosymbiont theory
they replicate like bacteria
they are able to make DNA into proteins
mitochondria and plastids have membrane proteins similar to bacteria
their ribosomes are similar to bacteria's ribosomes
cambrian explosion
535-525 million years ago -a sudden diversity of life during the cambrian period
the arms race between predator and prey getting tougher
the oxygen revolution
2.7 billion years ago, photosynthetic bacteria started to fill the world with oxygen
when is finally filled the atmosphere, original prokaryotes were destroyed
colonization of land
first plants and fungi
then arthropods 450 million years ago
then tetrapods 365 million years ago from lobe finned fishes
the first single celled organisms
1.5 billion years ago, fossilized stromalites
evolution is not goal oriented
evolutionary novelties
complex structures arise from gradual modifications of ancestral structures
such as the eye, starting with simple photoreceptor cells
they can retain their original purpose, like the eye, or be used for a different purpose, like the jaw bones being used for ear bones
evolutionary trends
species selection -like natural selection but on a species scale
the rise and fall of different groups of organisms according to different speciation and extinction rates
adaptive radiations -evolutionary change where many new species are formed to fill ecological niches
worldwide
mammals after the extinction of dinosaurs
groups of organisms that play new roles in their communities
such as plants that colonized land
regional
when organisms are in a new distant location where there is relatively little isolation
such as the silversword alliance in the hawain archipelago
mass extinctions
most species that have lived are extinct
mass extinctions are best documented for organisms that leave clear fossils
the big five (form the borders of eras)
444 million years ago
359 million years ago
66 million years ago, cretaceous extinction, killed half of marine life and many terrestrial including dinosaurs
generally thought to be caused by an asteroid
201 million years ago
252 million years ago, Permian extinction, between Paleozoic and Mesozoic eras, killed 96% of marine species
caused by volcanic eruptions
the sixth
the book says a sixth, human caused, mass extinction is likely (they also believe in global warming so I doubt them on this)
consequences
it takes 5-10 million years for the diversity of life to recover from a mass extinction
it can drasitcally change the types of organisms
for example a group of shell-drilling gastropods were wiped out during the mass extinction at the end of the triassic period
plate tectonics
earth's crust is plates that float on the mantle
they move at about a centimeter per year
or move toward each other, forming mountains
such as the indian plate crashing into the eurasian plate and forming the himilayas
or slide past each other, causing earthquakes
such as by the san andreas fault
they can move away from each other
such as the north american and eurasian plate
consequences of continental drift
it alters the habitat where organisms live
for example, the formation of pangea caused there to be less shallow oceans and a cold and dry interior
and the tip of southern Canada used to be in the tropics
it can also cause allopatric speciation when continents break apart
explains distribution of organisms
or marsupials being found only in australia
such as fossils of a certain reptile being found both in Brazil and West Africa
early earth and beginning of life
macromolecules
by dripping amino acids onto hot rock, researchers produces amino acid polymers, a complex mix of linked and cross linked amino acids
protocells
inside vesicles can be different than the environment inside
spontaneous bubbles of oil can have a semipermeable bilayer
small organic molecules
according to evolutionists, earth formed 4.6 billion years ago
it was bombarded by rock and ice until 4 billion years ago
the atmosphere had little oxygen, lots of water vapor and compounds released by volcanos
1920's Oparin and Haldane hypothesized that earth's early atmosphere was electron adding and that early oceans were full of organic molecules
1953 Miller and Urey created lab conditions thought to have existed on early earth
they found amino acids
some suggest that the early atmosphere was neutral
another hypothesis is that organic compounds were produced near alkaline hydrothermal vents
another hypothesis is that they came from meteorites
four hypothetical main stages are needed for cells to evolve
the joining of these into macromoleculs such as proteins and nucleic acids
the packaging of these molecules into protocells, bubbles of membrane
the abiotic synthesis of small organic molecules such as nitrogen bases amino acids
the origin of self replicating molecules
self replicating RNA
RNA can become a variety of shapes depending on its nucleotide sequences
2013 Szostak built a vesicle where RNA could be copied
if protocells with self copying RNA in it existed they would experience natural selection
the fossil record
how fossils are dated
radiometric dating -based on the decay of radioactive isotopes
carbon dating -based on a dead organisms ratio of carbon-14 to nitrogen-14 is considered accurate for fossils up to 75000 years old
for older organisms, they estimate the age of nearby volcanic rock
new groups of organisms
mammals have distinct features that can be fossilized, such as a jaw made of one bone
the fossil record is thought to show a smooth transition of the formation of these features
the fossil record
the fossil record is thought to show changes in the types of organisms that were on earth at different points and document emergence of new groups
the fossil record is incomplete
many organisms die and are not preserved as fossils
and existing fossils can be destroyed
it favors species with skeletons or other hard parts, and species that were widespread and abundant
most fossils are found in layers of sedimentary rock,
but some can be found in amber and ice
changes in genes in relation to changes in body form
developmental genes -large morphological differences can result from genes that alter the rate, timing, and pattern of development
changes in rate and timing -heterochrony
changes like this can alter adult forms, such as humans compared to chimpanzees
paedomophosis -sexually mature species still have juvenile features
such as axolotl salamanders that are mature while still having gills
changes in spatial pattern
homeotic genes decide where spatial features like branches or limbs go
hox genes provide this information to an embryo
the change in the positions of ubx and scr can convert a swimming appendage to a feeding appendage
development
changes in gene sequence
researchers inserted genes into drosophila flies to find the exact sequence that causes them to have six legs as opposed to crustaceans
changes in gene regulation
changes in organisms can be caused by changes in gene regulation instead of changes in the genes themselves
this is thought to be the cause of threespine stickleback fish losing their spines in lakes with less predators
chapter 26
phylogeny and taxonomy, "the tree of life"
evolutionary "history" from genome
gene duplications and gene families
gene families -groups of related genes within a genome (result of gene duplication)
homologous genes
orthologous genes -result of speciation event
for example cytochrome c between humans an dogs
paralogous genes - result of gene duplication
genome evolution
entire genomes if species are compared
humans are 99% similar to mice and 50% similar to yeast
humans have only 4x as many genes as yeast, but those genes are more versatile
phylogenies based on shared characteristics
inferring phylogenies using derived characters
these shared and differing characters can be used to put organisms in a cladogram
outgroup -closely related but not part of the group being studied
for example in the group of vertebrates, lampreys are an outgroup because they lack hinged jaws
phylogenetic trees with proportional branch lengths
in most cladograms the branching pattern is relative (earlier vs later)
however in some branch length can represent time
shared ancestral and shared derived characteristics
organisms have characteristics that they share with their ancestors and characteristics that differ
maximum parsimony and maximum likelihood
(or Occam's razor) the simplest explanation is the most likely
there are computers that can build parsimonious trees
cladistics
cladistics -common ancestry is the primary criteria for classification
groups of species are called clades
clades must be monophyletic
kinds of groups
paraphyletic -ancestral species and some descendants
polyphyletic -related species but not their common ancestor
monophyletic -ancestral species and all descendants
phylogenetic trees are hypotheses
they are constantly being changed and edited
the predictions they make are tested
such as the dinosaur fossil found over eggs
molecular clocks
applying a molecular clock
used to date origin of HIV
molecular clocks -an approach for measuring the absolute time of evolutionary assuming genes evolve at a constant rate
graphing number of genetic differences against dates from the fossil record
problems
some genomes evolve in irregular bursts
the same gene may evolve at different rates in different groups
the rate of the clock may differ between genes
there are deviations from the average rate of change
differences in clock speed
differences in rate of change of genes is related to how important the gene is
ones essential to survival will change very slowly
potential problems with molecular clocks
when they are extrapolated beyond fossil record
phylogenies from morphological and molecular data
morphological and molecular homologies
organisms that share morphological features are more likely to be related
however they can look very different and still be genetically similar as with the silversword plants
evaluating molecular homologies
homoplasies -organisms that coincidentally have many matching genes
organisms whose genes match more than 25% are considered to be homologous
otherwise similar DNA with a frame shift can appear very different
sorting homology from analogy
organisms can look similar but be analogous, the more features in an organism that look similar the more likely they are to be homologous
the "tree of life" is continually being edited
from 2 kingdoms to 3 domains
differences between prokaryotes led scientists to create a higher level of classification than the kingdom -the domain
the important role of horizontal gene transfer
transfer of genes from one genome to another
cases of this amongst early single celled organisms may have caused the beginning of the tree of life to look more like a web than a tree
phylogenies -trees of evolutionary relationships
linking classification and phylogeny
phylogenetic tree -branching diagram to represent evolutionary heritage
people have proposed basing all classification on evolutionary relationships
phylogenic trees
a split in these trees represents a common ancestor and the species immediately following the split are called sister species (such as chimpanzees and humans)
basil taxon - a lineage the diverges from other members of its gruop
hierarchical classification
species are placed into categories that become more and more specific
Domain
Kingdom
Phylum
Class
Order
1 more item...
they are grouped based on characteristics and do not always reflect evolutionary "history"
applying phylogenies
close relatives of an organism can be used for its genetic engineering
DNA can be used to determine what species something is
binomial nomenclature
common names can be inaccurate and are different in different languages
scientific names are binomial, the first part is genus (capitalized) and the second part is species (uncapitalized)
they are always latinized and italicized