Download Ch. 15: Evolution

Ch. 15: Evolution
I.
Darwin’s Theory of Natural Selection
Main Idea: Charles Darwin developed a theory of evolution
based on natural selection
A. Developing the Theory of Natural Selection
1. pre-Darwin: almost everyone believed the world was
about 6000 years old and that animals and plants were
unchanging
2. voyage of the HMS Beagle (1831-36): Darwin made
observations on different species of plants and animals
in South America and the Galapagos Islands.
3. Darwin hypothesized new species could appear
gradually through small changes in an ancestral species
a. artificial selection: humans promoting
certain traits in organisms through selective
breeding (ex: dogs, pigeons)
b. Darwin thought if humans could change
species, the same process could occur in
nature given enough time
4. natural selection: Darwin thought that nature could
produce new species if given enough time
4 basic principles
 individuals in a population show variations among
others of the same species
 variations are inherited
 organisms have more offspring than can survive on
available resources
 variations that increase reproductive success will be
more common in the next generation
5. The Origin of Species (1859): Darwin’s published
work on natural selection
6. evolution: cumulative changes in groups of organisms
through time
 natural selection is a means of explaining
how evolution works
B. Evolution and The Origin of Life
1. Evolution of life is linked to the physical and chemical
evolution of the Earth
2. Early Earth
a. Big Bang Theory - particles scattered and condensed to
form the Earth
b. After the Big Bang, Earth had the elements needed to
make biological molecules - carbon (methane), nitrogen
(ammonia), water, and hydrogen
c. Methane, ammonia, and water can combine (with
energy in the form of lightning) to form amino acid
3. The first protein
a. Remember - life is protein - "we're all just big bags of
enzymes"
b. How did the first amino acids assemble to make
proteins?
 Hypothesis: Naturally occurring clay
crystals served as templates for protein
assembly; amino acids break apart too easily
on their own
 Selection of specific assembled proteins
came about from "survival of the fittest"
 Nucleotides (RNA) may also have been
attracted to the clay particles and somehow
participated in protein synthesis - replaced
the clay particles
4. The first membrane
a. Proteins, by themselves, form spheres called
microspheres
b. Microspheres tend to pick up lipids from water outcome is a lipid film around protein
c. Membranes could have arisen through spontaneous,
but inevitable chemical events
5. The first organisms - metabolism
a. Probably anaerobic - produced ATP from anaerobic
glycolysis
b. Photosynthetic cells came along
 Photosynthesis changed the surface of the
Earth by increasing the oxygen supply
c. New organisms used oxygen to increase respiratory
efficiency
6. The first cell and the first multicellular organisms
(endosymbiont theory)
a. eukaryotic cells appeared about 1.8 billion years ago
b. may have lived closely with prokaryotic cells which
became organelles.
c. Chloroplasts and mitochondria may have been
prokaryotes that became organelles (both contain their
own DNA, ribosomes and divide independent from
the cell)
II. Population genetics - the study of inherited variation and its modulation
in time and space
A.Main concept: individuals do NOT evolve; populations do
1. Hardy-Weinberg principle: evolution will not occur in a
population unless there are forces that cause change in the allele frequencies.
B.
Factors bringing about a change
1.
Mutation - heritable change in kind, structure, sequence,
or number of component parts of DNA; introduces new
variation into population
2.
Genetic drift - random fluctuation in allele frequencies as
a result of random chance
a. founder effect: extreme example of genetic
drift when a small sample of a population
settles in a location separated from the rest
of the population (ex: Amish, Mennonites)
b. bottlenecks: occur when a population
declines to a low number then rebounds (ex:
cheetahs in Africa)
3.
Gene flow - change in allele frequencies: immigration
(come) and emigration (go)
4.
nonrandom mating: usually mating occurs bw
individuals in close proximity; leads to inbreeding
4.
Natural selection - differential survival and reproduction
within a population; natural selection acts to select the
individuals best adapted for survival and reproduction
C. Evolution of a species - a GRADUAL process
1.
Process by which species originate - speciation HOW??????
a)
Reproductive isolating mechanisms
1)
Mechanical - reproductive organs
2)
Gamete isolation - external fertilization (sea
urchin)
3)
Time isolation - species "in heat," or time of
emergence (cicadas)
4)
Behavioral isolation - dancing or other
reproductive ritual (ex: eastern and western
meadowlark have different mating songs)
5)
Hybrid inviability - incompatibility
(abortion); ex: mules, ligers
2.
Modes of speciation
a)
Allopatric (isolated location) - most common; no
contact with original population (usually a physical
barrier)
b)
Parapatric (transition location) - like mountains
and desert; some contact with original population
but offspring may not be successful or mating
behavior discourages interbreeding
c) Sympatric (ecological, behavioral, - barriers
WITHIN boundaries); caused by polyploidy (plants
and frogs) or when insects become dependent upon a
specific plant
III.
Evolution - proceeds by modification of the genetic makeup of
existing organisms
Macroevolution - large-scale patterns, trends, and rates of change
among groups of species
A.
Phenotype - morphological, physiological, and behavioral traits
of an individual
B.
Phylogeny - evolutionary relationships among organisms
C.
Systems of classification (Remember KPCOFGS?)
1.
Evolutionary taxonomy - based on a mixture of
morphological and evolutionary relationships (reptiles,
birds, and mammals grouped)
2. Cladistics - based on lines of decent (turtles, mammals,
lizards & snakes, crocodiles, dinosaurs, and then birds)
C. Patterns of evolution
1. adaptive radiation (divergent evolution)-one species
gives rise to many species in response to a new habitat
availability; often occurs after mass extinctions (ex:
mass diversity of mammals following dinosaur
extinction)
D.
2. coevolution: evolution of one species affects the
evolution of the other species in a close relationship
(ex: comet orchids and moth mutualism)
3. convergent evolution: unrelated species evolve similar
form, function and behavior due to inhabiting similar
niches
Rate of speciation
1.
Gradualism - morphological changes occur slowly
within a species
2.
Punctuation - morphological changes take place rapidly
during speciation
E. Evidence of Evolution
1. fossil record: important source of information for
determining the ancestry of organisms and the patterns of
evolution.
a. Transitional fossils: fossils that contain features
shared by different species.
i. Archaeopteryx: contains characteristics of a
bird as well as dinosaur features
b. derived traits: newly evolved features that do not
appear in the fossils of common ancestors (ex:
feathers)
c. ancestral traits: primitive features that appear in
ancestral forms (ex: teeth and tails)
2. Comparative anatomy: bones in vertebrates often have
similar bones but different functions
a.
homologous structures: anatomically similar
structures inherited from a common ancestor
ex: bird wings and reptile forelimbs are similar
in shape and construction indicating a common
ancestor
b.
vestigial structures: reduced forms of functional
structures in other organisms (ex: kiwi wings,
snake pelvis, whale hindlimb bones, human
appendix)
c.
analogous structures: structures used for the
same purpose but are not inherited from a
common ancestor (ex: eagle’s wings and a
beetle’s wings)
3.
Comparative embryology: studying evolutionary
relationship through vertebrate embryos
a.
Vertebrate embryos exhibit homologous
structures during development
b.
Ex: embryo tails and pharyngeal pouches
(become gills in fish or ears, jaws, and throats in
reptiles, birds and mammals)
c.
Shared embryo features suggests a shared
ancestor
4.
Comparative biochemistry: higher shared amino
sequences in certain proteins (ex: cytochrome c) and in
DNA and RNA mole indicate more recent common
ancestors in organisms
5.
Geographic distribution: organisms sharing the same
location share closer ancestors
F. Adaptation: a trait shaped by natural selection that increases an
organism’s reproductive success.
1. fitness: measure of the relative contribution an individual trait
makes to the next generation (often measured as number of viable
offspring an organism produces)
a.
camouflage
b.
mimicry
c.
antimicrobial resistance
2. Consequences of adaptation: not all features of an organism are
adaptive, but may arise as a consequence of other evolved
characteristics (ex: spandrel example, human helplessness at birth)