Transcript Evolution

Fossil: physical evidence of an org. that
lived long ago, most found in
sedimentary rocks
Help identify how ecosystems and org.
have evolved and changed.
Formation:
1. org. is buried in sediment soon
after it dies
2. sediments build up & stop decay
3. depending on conditions so portions
of the org. may be preserved or may
transform into rock
Types:
1. Trace: indirect evidence
-footprint, trail, or burrow
2. Casts: minerals fill in space left by org. after is
decays
3. Molds: Org. buried in mud decays leaving an
empty space
4. Petrified: minerals have replaced hard parts of
org.
5. Amber/Frozen: Org. is quickly encased in sap
or flash frozen
What can fossils tell us?
-information about structural relationships
e.g.-T-rex used big tail for balance
-footprints show behavior patterns, speed, &
relationships to other org.
-sediments help tell when org. lived & what the
env. was like
-fossils found in groups show behavior patterns
& relationships to other org.
-help create Geologic Time Scale-Earth’s
history divided into major eras & periods
based on physical & organic characteristics
Determining Fossil Age
-helps create fossil record (history of life)
1. Relative Dating: create a comparative age
of fossils based on their level in the rock
Interpretation for relative dating
-Correlation: matching rock layers in
different areas to show geographic &
organic evolution (in a specific region)
-Index fossil: org. that appeared over wide
ranges
-allows for relative dating between
different regions
-e.g. Trilobites
2. Absolute dating: provides an accurate age
-Radiometric dating: Elements decay over time
and change into different elements/isotopes.
-By measuring the ratio of isotopes/elements
in the rocks surrounding a fossil, its age
can be determined.
-Carbon-14 is used for organic fossils
-half-life = 5700 years
-it decays into Nitrogen-14
-can’t be used for org. older than 50,000 yrs
-Uranium-238 (half-life = 4.46 billion years) or
Potassium-40 (half-life = 1.27 billions years)
are used for older fossils
-must be tested on igneous (volcanic) rock
that is in the same layer as the fossil
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Evolution: change in the genetic make-up of
a population over time
-doesn’t have to create a new species,
may modify a population
-individuals don’t evolve, populations do
because an ind. genes don’t change
Macroevolution: evolution above the level of
species (speciation)
Microevolution: evolution at or below the level of
species
-changes in the genetic equilibrium of a
population based on differential reproduction
1809- J. B. de Lamarck
-1st major theory of evolution
-believed species aren’t constant, they evolve
from pre-existing species
-evolution involved 2 principles
1. Law of Use & Disuse
-the more an org. uses a body part the
stronger/better developed it becomes
2. Inheritance of Acquired Characteristics
-characteristics developed thru use &
disuse could be passed on
-e.g. giraffe’s
-theory incorrect because inheritance of DNA
isn’t affected by acquired characteristics
Charles Darwin: founder of the modern evolutionary
theory
-boarded HMS Beagle in 1831 as a naturalist on
5 year round-the-world trip
-collected org., rocks, & fossils
-recorded how species change over time
-most information collected from Galapagos
Islands (finches, tortoises, & marine iguanas)
-Once home he spent 20 years collecting &
analyzing data & experimenting
-Bred pigeons to demonstrate artificial selection:
breeding org. with specific traits to produce
offspring with desired traits
Natural Selection: survival of the best adapted
-based on which org. can survive and
reproduce more successfully
-changes allele proportions of the population
-survival of the “fittest” (best about to
reproduce)
Thomas Malthus: found that populations tend to
grown geometrically (2,4,8,16,32), but food
supply grow arithmetically (1,2,3,4)
-populations are kept in check by limiting
factors
Darwin used Malthus’ ideas to help create the
idea of natural selection
Coauthored paper with Alfred Russell Wallace
who was working on natural selection at the
same time. Darwin reported his findings first.
6 main points of Darwin’s theory
A. Overproduction: species produce extra
offspring because many won’t live to
reproduce
B. Competition: species must compete for
resources, not all survive
C. Variation: differences in characteristics of
inds. in a species
-variations that increase survival are passed
on
D. Adaptations: any trait the increases the
chance of survival & reproduction
E. Natural Selection: env. selects org. that are
best adapted to survive to reproduce & pass
on genes
F. Speciation: formation of new species
-over generations, adaptations accumulate
& result in new species
e.g. Giraffes
-some had longer necks & could reach food
unavailable to others
-as env. changed & grass disappeared those
who could reach leaves on trees survived &
passed on trait
Evidences
Of
Evolution
A. Fossils
-examining fossil evidence helps to create a
map of the org. that
have appeared
-determining age and
environment helps
link related org. and
show change over
time (precursors)
B. “Living Fossils”
-org. that have changed very little over time
-helps link current and past org.
-provides understanding of successful
adaptations
C. Structural Adaptations
-parts of org. that allow them to better survive &
reproduce
-e.g. Darwin’s Finches
D. Mimicry
-one species resembles another
-usually a harmless resembles a harmful
species
OR
-harmful species resemble each other
E. Camouflage
-enables species to blend into its surroundings
-harder for predators/prey to see & more likely
to survive/reproduce
F. Physiological adaptations
-Changes in an org’s metabolism due to
changes/mutations in DNA
-Causes:
-drug-resistant strains of bacteria & viruses
-need for a new flu vaccine every year
-chemical-resistant species of insects &
weeds
G. Homologous Structures:
-Body parts with similar
structure/arrangement,
function may be
different
-Shows phylogenetic
relationship
(phylogenyevolutionary
relationships)
H. Analogous Structures:
-Body parts with similar functions but different
structures
-Shows how the environment can “select” orgs.
with specific adaptations to be most
successful (natural selection)
-Don’t show phylogeny
I. Vestigial Structures:
-body parts found in present-day organisms that
no longer serve their original purpose
-may have developed into something else, or
may be non-functional
-still inherited because the DNA of that org. still
contains the information to make that part
J. Embryology:
-Comparing embryos of different organisms
-Scientists look for similarities
-e.g. tail, pharyngeal (gill) pouches
-Haeckel’s recapitulation theory
-Ontogeny recapitulates phylogeny
-development of the individual of every
species fully repeats the evolutionary
development of that species
-has proven to be incorrect
K. Biochemistry
-Comparing DNA, RNA, and proteins to identify
similarities in make-up
Organisms don’t change
because the environment
changes, the variations
already exist within the
population and some of
the individuals are more
successful.
Mechanisms
Of
Evolution
Populations evolve
-ind. can’t change their genotype over the
course of their lifetime
-evolution is a change in the genetic make-up of
a population over time
-Some genes are more successful (cause org.
to survive & reproduce better)
-Gene pool: all the alleles in a population’s
genotype
-Allelic frequency: % of a specific allele in the
gene pool
-Genetic equilibrium: pop. where the allelic
frequency doesn’t change over generations
Is this population evolving?
-pop. that is in genetic equilibrium is not
evolving
-mutations cause new genes/alleles/
phenotypes to appear in a population
-many are lethal and quickly eliminated
-some have no effect
-those that are beneficial will be passed on
Gene flow
-can change the allelic frequency
-immigration: movement of ind. into population
-emigration: movement of ind. out of population
Genetic drift: alteration of allelic frequencies by
chance events
-occur in small, isolated populations that have
become separated from their original gene
pool
-new pop. gene pool is different from original
Speciation:
-evolution of a new species
-ind. of similar pop. no longer interbreed
-can occur when a pop.
gets divided by a
physical barrier
(Geographic
isolation)
-Reproductive isolation – can occur by
geographic isolation, drift, or mutations
-some change causes ind. to stop
interbreeding
-Polyploidy – change in the chromosome
number
-usually changes in sets
-can be 3n (3 sets of each chromosome) or
more
-common in plants
-can cause isolation & speciation
-Adaptive radiation: species evolves in an area
with several different habitats
-variations within the pop. cause different
ind. to be better adapted to one habitat
-causes several species to form at the same
time from the original pop.
Patterns
Of
Evolution
Divergent Evolution: species that were similar
(or from the same ancestor) become different
due to isolation, adaptation, & natural selection
Convergent Evolution: unrelated species evolve
similar traits due to similarities in environmental
pressures
-analogous structures
Gradualism: idea the species gradually change
over time due to accumulated adaptations &
changes in allelic frequencies
Punctuated equilibrium: speciation occurs in
rapid bursts w/ long periods of genetic
equilibrium