Download Chs. 14-16: Evolution

Chapters 22-25
Evolution
Evolution
The definition of Evolution is:
change over time
Biological Evolution is:
genetic change in population over time
process by which modern organisms
have descended from ancient
organisms (slow change over long
time)
• Even relatively quick evolution takes
hundreds of thousands of years
History of Evolutionary Theories
Plato (427-347 B.C.) 2 worlds – 1 perfect, 1
imperfect. No change in organisms
Aristotle (384-322 B.C.) Organisms placed
on “ladder of complexity / perfection” (scala
naturae) No change
Judeo-Christian culture tried to explain the
Creator’s plan as observable, natural
phenomena – Natural Theology
History of Evolutionary Theories
Carolus Linnaeus (1707-1832) Designed
modern taxonomic system (binomial
nomenclature)
From this system, we can (he didn’t) now
infer evolutionary relationships between
different groups
Geologists:
Georges Cuvier
James Hutton
Charles Lyell
History of Evolutionary Theories
Georges Cuvier (1769-1832) helped
develop Paleontology – study of fossils
Discovery of fossils (extinct species,
similarities to modern species) put some
doubt into Earth’s age and the origin of
species
Cuvier explained differences in strata with
“catastrophism” – floods, droughts,
volcanoes, etc. changed local areas
drastically over short periods of time
• Organisms did not change, just migrate
History of Evolutionary Theories
James Hutton (1726-1797) proposed that
rocks, mountains, and valleys have been
changed by water, wind, temperature,
volcanoes, and other natural forces
He described the slow processes that shape
Earth as “gradualism”
History of Evolutionary Theories
Charles Lyell (1797-1875) – agreed with
Hutton and said that scientists must always
explain past events in terms of observable,
PRESENT events and processes
(“uniformitarianism” – what happens today
happened yesterday)
They theorized Earth was much
older than a few thousand
(6,000) years, which didn’t
set well in the traditional
timeframe of Creationism
Age of the Earth
We now know Earth is approximately 4.5
billion years old
Darwin used the work of Hutton and Lyell as
a basis for his theories of slow change over
time. Darwin’s work was a biological
duplicate of Hutton and Lyell’s works in
geology.
Geologists study Earth’s rocks
Fossils are preserved
remains of ancient
organisms
As fossils are found that
don’t resemble organisms today,
evidence increases that Earth has
changed and that organisms have
changed with it
Biologists and geologists date Earth’s
past with the help of rocks
Geological Time Scale
RELATIVE DATING
Technique used to determine age of
fossils relative to other fossils in
different strata
This technique is VERY approximate
Geological Time Scale
ABSOLUTE (RADIOMETRIC) DATING
Using radioactive elements in rock
that decay at a steady rate to
determine age
Decay measured in terms of HALFLIFE
• Half-life – time required for half the
radioactive atoms in a sample to
decay
Radioactive Decay
During radioactive decay, the atoms of
one element break down to form
something else
Lose a
proton
6 protons
4 neutrons
5 protons
4 neutrons
Rocks contain radioactive elements, each
having a different half-life
EXAMPLES:
Uranium-238  Lead-206
HL = 4.5 B yrs
Potassium-40  Argon-40 HL = 1.3 B yrs
Carbon-14  Nitrogen-14 HL = 5770 yrs
Scientists often date rocks using
Potassium-40, which decays to form the
stable element Argon-40
It has a half life of 1.3 billion years
This is used to date the oldest rocks on
earth
K-40
Formed
K-40 Ar-40
Ar-40
1.3 B yrs
2.6 B yrs
Uranium and Potassium are useful for
dating rocks
Carbon-14 is useful for dating things that
were once alive such as wood, natural
fiber, or cloth
C-14 is in the atmosphere; living things
take it in their cells. After the organism
dies, it doesn’t take in any more C-14.
We can then compare the amounts of
C-14 to N-14, knowing its half-life, to
determine the age of the sample
Fossil Evidence
Found in Sedimentary rock:
layers of sand, silt, and clay in streams,
lakes, rivers, and seas form rock that
may have trapped living organisms
Fossil records – Show change over time.
Some time frames are missing, but will
show change of climate and geography.
Ex: Shark teeth in Utah
How can this be?
Jean Baptiste de Lamarck
(1744-1829)
He also recognized that organisms were
adapted to their environments and that
they change
He relied on three ideas:
1. A desire to change (innate drive for
perfection)
2. Use and disuse (Giraffe’s necks and
vestigial organs)
3. Inheritance of acquired characteristics
Darwin’s Dilemma
Set sail around the world in 1831 on
HMS Beagle on a 5 year voyage
He had prior knowledge of geology
(Lyell was a good friend) and
agriculture that helped influence the
development of his theory
Anchored all along the way
and took samples from
each place
Darwin’s Dilemma
He collected and studied beetles from
Brazil, birds from Chile, and iguanas,
tortoises, and finches from the
Galápagos Islands
He noticed similarities between
mainland (Ecuador) and Galapagos
finches
Later, he noticed differences in beak
size among finches from different
islands in the Galapagos
Darwin’s Dilemma
Thomas Malthus – wrote paper on
population growth in Great Britain
Population grows exponentially
Limiting factors on growth (carrying
capacity)
• Food
• Area
• Resources
Darwin’s Dilemma
Darwin applied Malthus’, Hutton’s, and
Lyell’s work to species’ ability to change,
and called the mechanism Natural
Selection
Nat.Sel.: Process by which organisms
with favorable variations survive and
produce more offspring than less welladapted organisms
He was sure Nat.Sel. was true,
but he feared public ridicule. So,
he kept his ideas to himself
Darwin’s Dilemma
Alfred Russel Wallace (1823-1913),
working independently, came to the
same conclusions as Darwin
He sent a manuscript to Darwin, basically for
proofreading
“I never saw a more striking coincidence…
so all my originality, whatever it may amount
to, will be smashed.” – Charles Darwin
Letter to Charles Lyell, June 18, 1858
Darwin quickly abridged and published his
work “On the Origin of Species”
Darwin’s Natural Selection
Ernst Mayr, an evolutionary biologist, has
dissected the logic of Darwin’s theory into
three inferences based on five
observations (Pg. 435)
Observations:
Tremendous fecundity
Stable populations sizes
Limited environmental resources
Variation among individuals
Heritability of some of this variation.
Darwin’s Natural Selection
Observation #1: All species have such
great potential fertility that their population
size would increase exponentially if all
individuals that are born reproduced
successfully.
Darwin’s Natural Selection
Observation #2: Populations tend to remain
stable in size,except for seasonal
fluctuations.
Observation #3: Environmental resources
are limited.
Darwin’s Natural Selection
Inference #1: Production of more
individuals than the environment can
support leads to a struggle for existence
among the individuals of a population, with
only a fraction of the offspring surviving
each generation.
Darwin’s Natural Selection
Observation #4: Individuals of a
population vary extensively in their
characteristics; no two individuals are
exactly alike.
Observation #5: Much of this variation is
heritable.
Darwin’s Natural Selection
Inference #2: Survival in the struggle for
existence is not random, but depends in
part on the hereditary constitution of the
individuals.
Those individuals whose inherited
characteristics best fit them to their
environment are likely to leave more
offspring than less fit individuals.
Darwin’s Natural Selection
Inference #3: This unequal ability of
individuals to survive and reproduce will
lead to a gradual change in a population,
with favorable characteristics
accumulating over the generations.
Evidence in Living Organisms
Comparative embryology:
All vertebrate embryos look similar to
one another in early development, with
the development of a tail and gill
arches
• Ernst Haeckel made early drawings
– later exposed as frauds.
• Gave fuel to anti-evolutionists
Evidence in Living Organisms
Comparative embryology:
These anatomical similarities indicate
similar genetics are at work
Become more dissimilar as they grow
• Cell specialization and differentiation
Common ancestor?
Evidence in Living Organisms
Evidence in Living Organisms
Comparative anatomy:
Homologous Structures
Analogous Structures
Vestigial Organs
Evidence in Living Organisms
Homologous Structures –
structures that are similar in
anatomy, but may serve very
different functions
Ex: cat, whale, and human
forearm
Homologous Structures
Flying
Swimming Running Grasping
Evidence in Living Organisms
Analogous Structures – structures
that serve similar functions, but
have evolved independently of each
other
Not homologous;
analogous
Not homologous;
not analogous
Homologous;
not analogous
Homologous;
analogous
Evidence in Living Organisms.
Vestigial organs – organs that have little
or no purpose in the organism; may
become smaller or even disappear
Ex: Tailbone or appendix in humans
Ex: Tiny leg bones in
snakes (boas and pythons)
thought to come from 4
legged ancestor
Evidence in Living Organisms
Comparative biochemistry and
molecular biology:
All cells have DNA, RNA, ribosomes,
the same 20 amino acids and use
ATP to do work
Similarities in biochemistry indicate
relationship
Evidence in Living Organisms
Cytochrome c
is a highly
conserved
respiratory
protein
containing 104
amino acids in
humans
Evidence in Living Organisms
Amino acid
differences of
hemoglobin
between
species