Transcript Evolution and the History of Life

Evolution and the History
of Life
MLK
Fall 2005
M.Elizabeth
www.marric.us/teaching
• Chapter 8.1 Change Over Time
– Differences Among Organisms
– Do Species Change Over Time
– Evidence of Evolution: The Fossil Record
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Fossils
Reading the Fossil Record
Gaps in the Fossil Record
Vestigial Structures
– Case Study: Evolution of the Whale
– Evidence of Evolution: Comparing Organisms
• Comparing Skeletal Structures
• Comparing DNA from Different Species
• Comparing Embryonic Structures
Changes Over Time
• Differences between species relate to
adaptations.
• Adaptations – a hereditary characteristic
(attribute) that helps an organism survive
and reproduce in its environment.
•
– Physical adaptations are heredity. Which
means that the organism has no choice about
the characteristics.
– Emotional, cultural, and behavioral
adaptations are choices that humans can
make.
It’s all about Species
• What is a Species?
– A population of organisms that can mate
with one another produces fertile offspring.
• Example: Horses, Donkeys, and Mules
– Breeding a male donkey to a female horse results in a mule;
– Breeding a male horse to a female donkey produces a hinny
+
=
Sterile Mule
Horses and Donkeys are separate species
Do Species Change Over Time
The Earth is very old – 4.6 Billion Years
• The Earth was formed approx. 4.6 bya
– The oldest rock is 3.5 Billion years
• Fossil evidence suggests that species have
changed over time because younger fossils
are different, yet similar to older fossils.
Evolution
• Evolution is the process by which
populations of organisms acquire and
pass on unique traits from generation to
generation, affecting the overall makeup
of the population and potentially leading
to new species.
Four distinct mechanisms generate evolution
(change in allelic frequency in populations
over time):
1. mutation
2. gene flow
3. genetic drift
4. selection (natural and “artificial”)
Geologic Time Notations
ya – Years Ago
mya – Million of years ago
bya – Billion years ago
Precambrian
Paleozoic ERA
Mesozoic ERA
Cenozoic ERA
Era word roots
• Geologist use the clues in some of these words.
• For example:
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zoic refers to animal life
paleo means ancient
meso means middle,
ceno means recent.
• So the relative order of the three youngest
eras, first Paleoozoic, then Mesozoic, then
Cenoozoic, is straightforward.
Evidence of Evolution: The Fossil
Record
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Fossils
Reading the Fossil Record
Gaps in the Fossil Record
Vestigial Structures
Fossils
• Are found in the
earth’s crust – the
very uppermost
part of the earth
that is exposed to
the surface or
lying immediately
below the oceans.
The Best Crust for Fossils
• Sedimentary Rocks are the best crust for
fossil formations;
Example: The
Grand Canyon.
Strata = Layers
of sediment so
its called
sedimentary
rock
Rocks contain clues to the Earth’s past.
What are Fossils
• Fossils are the mineralized remains of
animals or plants or other traces such as
footprints.
• All of the fossils and their placement in
rock formations and sedimentary layers
(strata) is known as the fossil record.
• The study of fossils is called paleontology.
What kind of rock is this?
Sedimentary Rock
Law of Superposition:Youngest on Top
• An undeformed sedimentary rock layer is
older than the layers above it and younger
than the layers below it
D
C
B
A
Law of Superposition
• In terms of Relative Age
• Rock Layer B must be younger than Rock Layer A
• but
Rock Layer B is older than Rock Layers C and D.
D
C
B
A
• Once the order of formation is known, a
RELATIVE AGE can be determined for
each rock layer
http://pubs.usgs.gov/gip/fossils/
Gaps in the Fossil Record
• Occur because specific conditions are needed for
fossils to form
• Organisms with hard body parts (skeletons) are more
likely to form fossils than organisms with soft body
parts. Basic to this is the organisms cannot be eaten
before fossilization
– Find shells and bones
• Fossils form best without oxygen – why peat bogs and
tar pits have great fossils. Burial by sediments reduce
oxygen exposure.
• Freezing also allows fossil formation – Mammoth that
Japanese scientists are trying to clone from DNA
extracted from frozen Mammoth fossil.
• Fossils once formed must not be destroyed.
Sea shells embedded in
marine rock near Santa Cruz
Ammonites near
Redding
Human Remains
Vestigial Structures
• Mammals are warm blooded vertebrates
• Vestigial structures are organs that have
no apparent function.
• Examples:
– Human appendix – narrow tube attached to
the large intestines
– Chimpanzee, gorilla, and orangutan appendix
is functional and used to help digest tough
plant material
Appendix
Whale evolution
(terrestrial to aquatic in ~ 8 Myr)
8 million years total
PBS Whale Evolution
One structural remnant (remaining part) of this
evolutionary process are hind limb bones. These
bones are called vestigial structures.
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html
Evidence of Evolution:
Comparing Organisms
• Comparing Skeletal Structures
• Comparing DNA from Different Species
• Comparing Embryonic Structures
Comparing Skeletal Structures
• Homologous Structures
– Having similar origins and anatomical
patterns
– Examples – bird wings, human arms, whale
flippers, bat wings, cat legs.
Homologous Structures
Analogous Structures
• Analogous structures
do the same thing –
similar function, but
different anatomy.
– Wings (butterfly
external skeleton,
bat internal skeleton
• Analogous structures:
wing of an insect, bird,
bat and pterosaur
Comparing DNA from Different
Species
• The actual molecular characteristics of
DNA is measured and compared to other
organisms.
• There are four different nucleotides in
DNA (Adenine, Guanine, Cytosine, and
Thymine).
• Gene sequencing – sections of DNA are
sequenced for the order of nucleotide
bases (ATCG or ATGC or ACTG, etc).
What We've Learned So Far
• By the Numbers: What Does the Draft Human
Genome Sequence Tell Us?
• The human genome contains 3164.7 million
chemical nucleotide bases (A, C, T, and G).
• The average gene consists of 3000 bases, but
sizes vary greatly, with the largest known human
gene being dystrophin at 2.4 million bases.
• The total number of genes is estimated at
30,000 —much lower than previous estimates of
80,000 to 140,000.
• Almost all (99.9%) nucleotide bases are exactly
the same in all people.
• The functions are unknown for over 50% of
discovered genes.
Looking for Relatedness
Crime Solving:
The COmbined DNA Index System, CODIS, blends
computer and DNA technologies into a tool for
fighting violent crime.
Comparing Embryonic Structures
• Ontogeny: Development of the Individual
from conception to death.
• Phylogeny: Development of the Species.
• Vertebrate organisms (those having a
backbone) have similar stages of life as
an embryo
Open Court
Publishing
Company
Chapter 8.2 How Does Evolution Occur
• Charles Darwin
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Darwin’s Excellent Adventure
Darwin’s Finches
Darwin Does Some Thinking
Darwin Learned from Farmers and Animal
and Plant Breeders
Darwin Learned from Geologists
Darwin Learned from the Work of Thomas
Malthaus
Natural Selection
More Evidence of Evolution (DNA Mutation)
Darwin’s Excellent Adventure
• HMS Beagle – Galapagos Island Travels
• Galapagos Islands are part of the country
of Ecuador though the islands are about
1,000 kilometers west of the continent of
South America in the Pacific Ocean.
There are 19 volcanic islands with a land
area of 8,000 km2 in an area of the Pacific
Ocean over 60,000 km2
About Darwin
http://www.aboutdarwin.com/timeline/time_01.html
Darwin’s Finches
Diversity
• Darwin saw finches that were very
different from each other as he traveled
to the various islands of the Galapagos.
• Because of their physiological differences
(beak shapes), the finches had very
different diets
The diversity of life…
Although there is unity in life there is also a
great deal of diversity!
Estimates of Diversity:
~1.7 million cataloged species
50,000 vertebrates
260,000 species of plants
750,000 species of insects
Total diversity  5-30 million species !
Darwin Does Some Thinking
• Darwin wonders how did the finches
become so different. He thought maybe
there was a storm that separated the
original population resulting in geographic
isolation (one of the ways that speciation
can occur)
Darwin Learned from Farmers and
Animal and Plant Breeders
• Darwin was very familiar with artificial
selection or better known as selective
breeding.
• Certain traits are determined by the
breeder to be favorable. If only those
organisms with the favorable traits are
breed then the trait will occur more often
in the population. By isolated certain
individuals the differences can grow.
All from an ancestral dog
Darwin Learned from Geologists
• Darwin learned from Charles Lyell that
the Earth was formed over a long period
of time by natural process.
• This idea of geologic time (really really
long time ago) helped Darwin to more
seriously consider natural processes for
changing populations.
Darwin Learned from Thomas Malthus
• Thomas Malthus was an economist.
• Malthus reasoned that humans have the
potential to reproduce beyond the capacity
of their food supply.
• Malthus recognized that there are some
limitations to human population growth:
– War (for animals it is predation-predators)
– Disease
– Starvation
Competition
• Because there are some limitations to
growth, Darwin thought that those
survivors must be better equipped
(adapted) to their environment allowing
them to out-compete other individuals.
• The offspring of the successful
competitors have the same traits so are
also more likely to survive in the same kind
of environment.
Natural Selection
Darwin theorized that evolution occurs through a
process he called natural selection
1. Overproduction – Each species produces more
offspring that will naturally survive.
2. Genetic Variation – individuals will be slightly
different from one another.
3. Survival Struggle – competition for resources
Abiotic and Biotic factors
4. Successful Reproduction – fitness
(Survival of the fittest)
More Evidence of Evolution
• Darwin did not know what the mechanism
was for how parents passed their traits to
their offspring.
• Gregory Mendel (1822-1884) the Catholic
monk studied traits in sweet peas.
• With Mendel's work and biochemistry we
now know that the mechanism is meiosis
involving DNA that is subject to mutation.
Mutation
• Changes to the heredity material- DNA,
deoxyribonucleic acid – result in a changed
genotype.
• Some changes that occur are not observed
because the change did not significantly
affect a function. Changes that affect
function result in a different pheonotype
(what things look or function like).
Types of Mutation
• Changes can occur by
• single nucleotide substitutions
• Insertions or deletions of longer
sequences of nucleotides (the components
that make up deoxyribonucleic acid
• Chromosome alterations – which can be
seen with a microscope.
Some Phrases about
Evolution
Asking and Answering “How?”
and “Why?”
• How and why questions are usually
answered using a hypotheticaldeductive (H-D) approach.
– hypothesize
– predict
– test! - experiments (field + lab)
Hypothesis vs. Theory
“Evolution is just a theory”
Scientific theories are factual
statements about Nature.
Good theories are logically
supported
and are demonstrated by the
results from multiple tests.
“Evolution is about the
Origins of Life”
The Theory of Evolution mostly
describes how change occurred
after complex life arose.
"Nature red in tooth and
claw"
Evolution says nothing about
which traits will evolve;
only that they will change.
"Survival of the Fittest"
Cultural and ethical decisions of who is
“fittest” and should survive are not Nature’s
Laws. The term is used in business but with
a different definition of fittest
This is different from…..when fitness
involves reproduction and those
organisms that reproduce have
demonstrated fitness.