Evolution
General complexity over time
• Fossils resembling clams and shrimp fish
 to lizardlike creatures on land  birds
 mammals
• When animals die, they eventually are
covered by a mudslide, and then over
time sedimentary rock – layers of minerals
and fragments of other rocks deposited
over time, covers them.
Rocks and Fossils
• The older the rocks, the
older and more primitive
are the animals discovered
within them.
• Exist as fossils – preserved
remnants of a once-living
thing.
• Gaps in fossil record
because fossils usually form
in water, not on land
• The most common are
impressions left in
sedimentary rocks, but
no always. i.e. woolly
mammoths found in
glaciers
Sidebar: Bringing the Mammoth
Back
• It is possible to take the
•
•
DNA of a mammoth and
implant it into an
elephant egg and give
birth to a live mammoth
again. Coming
soon…same as dodo bird.
http://news.nationalgeogr
aphic.com/news/2005/04
/0408_050408_woollyma
mmoth.html
“Let’s cuddle” 
History of Life on Earth
• Earth is 4.6 billion years old
• Geologists divide history into four units of
time called eras, which are subdivided
into periods and epochs
• Most bottom rocks are oldest – ones at
the top are youngest
Radioactive Dating
• More accurate way of dating fossils and rocks
• Some elements are radioactive and break down
•
at predictable rates called the half-life of an
element – the amount of time it takes for one
half of the radioactive atoms to disintegrate
i.e. half-life of uranium is 700 million years –
breaks down to lead i.e if we have a sample with
25% uranium and 75% lead, 1.4 billion years
have passed.
The Origin of Life
• Pre-photosynthetic organisms, atmosphere likely
•
was composed of CH4, NH3, H2, and H2O vapour
Rains and comets fell on barren rocks forming
oceans
The Origin of Life
• Planet bombarded with energy from ultraviolet
light and lightning
The Origin of Life
• This energy rearranged the chemical bonds of
molecules in the atmosphere, creating a large
number of organic chemicals built up in the
primitive oceans over millions of years.
The Origin of Life
• HETEROTROPH HYPOTHESIS: Originated by A.I Oparin in
1930’s, stating that the first organisms used organic molecules in
the ocean as a food source.
• fossil microbe-like objects are dated to be 3.5 billion years old.
• Photosynthesis is 2.4 billion years old
Stanley Miller Experiment
• Early 1950’s – after
•
several days, electricity
applied to these gases
produced amino acids,
the building blocks of
proteins.
Proved organic molecules
could form from inorganic
substances, though not
proof how first cell came
to being
Abiogenesis
• Also known as biopoesis:
•
•
study of how life arose from
inanimate matter
Major question: Which
came first, proteins or
nucleic acid?
Phospholipids form bilayers
in water while under
agitation– the same
structure as in cell
membrane
The Origin of Autotrophs
• Autotroph: orgainism which makes its own food
• First organisms were heterotrophs and anaerobic
• As food became scarce, organims that produced own
•
•
food from sunlight were favoured
Then, as photosynthetic organisms arose, some
heterotrophs would start using them as a food source
Oxygen released into atmosphere from autotrophs
meant change in atmosphere, and therefore allowing
aerobic respiration which releases far more energy than
anaerobic respiration
Multicellular Organisms
• First autotrophs and heterotrophs were
single-celled
• 570 million year old fossils rare
• Fossils younger than this show fossils from
all major groups of animals and many
groups of plants that are alive today
• Worms, corals, shelled animals like clams,
animals resembling lobsters, crabs and
relatives of today’s starfish
Why did they appear so fast?
• One hypothesis is that earlier organisms had soft
•
•
bodies that did not fossilize easily, so it only
appears quick
Cambrian Explosion 530 million years ago
Fossil record shows evidence of groups of
organisms that became common than became
extinct. This historically is the norm – 99% of
all things that have ever lived are extinct
Extinct
Dinosaurs
• Roamed for about 200 million years
• Died about 60-65 million years ago – most popular
•
•
•
theory is an asteroid impact, but could be a combination
of other factors as well i.e. volcanic activity, ice age,
disease
Scientists have described over 1.7 million of the world's
species of animals, plants and algae, as of 2010.
Thought to be 4 to 6 million on earth
http://www.scienceagogo.com/news/20020328223914da
ta_trunc_sys.shtml
Theories of Evolution
• Until 19th century, people were puzzled by
fossils of organisms
• Most scientists thought things were
distinct and unchanging
• Dinosaurs and woolly mammoths could
not be explained
Jean de Baptiste Lamarck
• French naturalist –
observations of fossils
challenged the
common idea that
species were fixed
types – organisms
change through time
1798
Jean de Baptiste Lamarck
• In 1809, proposed that organisms evolved
in response to their environment
• Evolve: change from one form to another
• First to suggest that animals undergo
evolution.
Jean de Baptiste Lamarck
• Explained two facts:
• 1) The fossil record: showed that
organisms in the past were different from
those living from today
• 2) explained why each organism was so
well adapted to their environment –
organisms ha
have adaptations that suit
their particular way of life
Jean de Baptiste Lamarck
• Explained a mechanism:
• Animals have acquired characteristics - the traits that
•
•
•
an organism has acquired throughout its lifetime are
passed down to their offspring.
For example, if a parent learned to play piano, their child
would be born knowing how to play piano
Giraffes have aquired longer necks over time by
stretching to reach taller trees.
Even scientists then did not believe him: EPIC FAIL! We
now know we have genes, and that new traits are only
passed on by on by random, rare mutations
Jean de Baptiste Lamarck
• They didn’t believe him that species
gradually changed through the ages, and
on that, they were wrong, not Lamarck
DARWIN: DA MAN!!!
• 50 years after Lamarck
• 1859 wrote on The
Origin of Species by
Means of Natural
Selection
• Also stated living things
•
gradually evolve
adaptations to the
environment
Difference was in the
mechanism
Charles “Da Man” Darwin
• Unlike Lamarck, Darwin recognized the
variations among members of a species
which are inherited
• Natural selection: process by which
heritable traits that make it more likely for
an organism to survive and successfully
reproduce become more common in a
population over successive generations.
Natural selection
• Realized that most organisms produce
more offspring that can survive.
• There is competition amongst offspring to
survive, whether plant or animal, which
results in the survival of only a few
• Only those organisms most suited for the
environment survive to produce offspring
“survival of the fittest”
Summarizing Natural Selection
• 1) Species have the ability to produce a large number of
•
•
•
•
•
offspring
2) The resources of the natural world are limited
3) Therefore, there must be competition for survival
among the offspring in each generation
4) There is great variability within populations of
organisms. No two organisms are the same. Much of
the variability/variety is inherited
5) The organisms that survive and produce offspring are
those that have inherited the most beneficial traits for
surviving in that particular environment
6) As this process continues through many generations,
the population gradually becomes better adapted to the
environment
Key Points
• Variations in a population occur randomly.
• They do not arise in response to the
environment
• Natural selection “selects” from among
those traits that already exist within the
gene pool.
What Darwin didn’t know
• Didn’t know about genetics.
• Didn’t know about Mendel…the monk’s work was
•
•
•
available but remember, no one read it
We now know about random mutations and that
they arise “INDEPENDENTLY” of an organism’s
needs
Usually they are not useful, but sometimes they
are
Only those that are useful will increase an
organisms chance of survival
TONIGHT’S HOMEWORK
• Look over these notes. Summarize the key
points.
Comparing Darwin and Lamarck
• A cheetah’s speed – both would say it’s because of
•
•
EVOLUTION but:
LAMARCK: “As cheetahs run after their prey, they
developed strong legs, which were then passed
down to future generations”
DARWIN: “No, you putz, natural selection acted
upon variation in the cheetah population. Within
the population, some cheetahs had the ability (from
birth) to run faster than others, and since it helped
them catch prey better, they were able to live to
produce offspring and pass the genes onward.
Comparing Darwin and Lamarck
• The biggest difference is when variation
occurs in a population. For Lamarck
variations come about as a result of a
change in the environment. As prey runs
faster, the evolves greater speed.
• For Darwin, variations exists
independently of the environment, not in
response to environmental conditions
Evidence of Evolution
• Fossils proved that species existed in the
past that do not exit now
• However, most evolution is slow, and hard
to observe
Evidence from Structure
• Homologous structures: structures with different
•
functions but common ancestry
i.e bird wing and dog arm – still very similar in structure
Evidence from Structure
• Vestigial Organs: small or
•
•
incomplete organs that
have no apparent
function
Remaining parts of oncefunctioning organs – of a
previous ancestor
Whales evolved from four
legged ancestor – hip and
femur still resides, though
not used. Neither affects
reproduction of whale
either, thus, carries on in
future generations
Whale
Evidence from Embryology
• Embryo: a developing
•
•
•
organism
Embryology: study of the
development of an
organism
Developmental stages of
many animals look
similar…hence proof of
common ancestor
The more closely related
the species, the more
similar embryological
patterns shared by
organisms
Embryology from Biochemistry and
Genetics
• Genetic code, DNA, is used to code for proteins
• A universal genetic code is consistent with the idea that all organisms
•
•
evolved from a single organism that used that code.
Biochemists compare amino-acid sequences of proteins found in different
organisms
More similar organisms – more similar amino-acid sequences and vice versa
Observed in Nature
• Peppered moths in 1850’s England used to be white to
•
•
blend with trunks – rarely saw black ones.
With industry in 1900’s, industry darkened tree trunks,
black moths started out competing white moths –
invisible to predators
Since pollution controls, white moths are making a
comeback
Observed in Nature
• Evidence that a species of fireweed
formed by doubling of the
chromosome count, from the
original stock.
• 1989 issue of Scientific American.
It's called "A Breed Apart." It tells
about studies conducted on a fruit
fly, Rhagoletis pomonella, that is a
parasite of the hawthorn tree and
its fruit, which is commonly called
the thorn apple. About 150 years
ago, some of these flies began
infesting apple trees, as well. The
flies feed and breed on either
apples or thorn apples, but not
both. There's enough evidence to
convince the scientific investigators
that they're witnessing speciation
in action.
Controversy
• Many people still don’t believe in evolution
• They may believe in Intelligent Design or Creationism
• The Scopes Monkey trial was the OJ trial of its time. Happened in 1925, it
•
discussed the issue of teaching evolution in school. Involved agnostic
defence lawyer Clarence Darrow (thought to be one of the best in history)
against five time (failed) Democratic nominee for president William
Jennings Bryan (he died five days after winning)
A great movie/book on this topic, though dramatic and a tad inaccurate, is
called Inherit the Wind. See the Spencer Tracy version.
The Process of Evolution
• Evolution tends to work slowly over time
• Changes in traits happen through random
mutation – this mutation only has chance
of staying in the population if it does not
negatively affect the ability of the animal
to pass on its genes
• Over time, natural selection can alter gene
frequencies
Speciation
• Means the formation of new species
• Species: a taxonomic rank (the basic
rank of biological classification) whose
members can interbreed to produce fertile
offspring
Speciation
• Often happens when a population
becomes isolated from the rest through
geographic isolation: a physical barrier
separates a population
• No two environments are identical, so
selective pressures that occur in one
location may be different from the
pressures in another location
Abert squirrel and Kaibab squirrel
• Live on opposite sides
•
of the Grand Canyon
Once part of same
population before
Colorado River took a
separate course 1
million years ago,
splitting it in two
Abert squirrel and Kaibab squirrel
• Different
• A.S
•
• K.S
characteristics
favoured each on
both sides of the
canyon
Finally became two
different species,
where they could no
longer interbreed
Reproductive Isolation
• When species which live in the
same area breed at different
times of the year
• i.e. toad species Bufo
americanus and Bufo fowleri .
The members of these species
can be successfully crossed in
the laboratory producing
healthy, fertile hybrids.
However, mating does not
occur in the wild even though
the geographical distribution of
the two species overlaps
B.A
B.F
Adaptive Radiation
• When many new species evolve from a
single ancestral species
• Often occurs when a species enters a new
environment where there are few other
competing species
Adaptive Radiation
• i.e. finches in the Galapagos Islands: volcanic islands that lie 1000
km west of South America
• Darwin visited them when he was young
• Each island was distinct from the other, hence the single species of
finch which inhabited each island eventually diverged to different
species with differing beaks, feeding habits and behaviours adapted
to the local food
Convergent Evolution
• describes the acquisition of the same biological trait in
•
•
•
•
unrelated lineages
Organisms may have the same adaptation but are not
closely related
Occurs when the environment puts similar selective
pressure on different species
i.e. the wing-although their last common ancestor did not
have wings, birds and bats do, and are capable of
powered flight
Traits arising through convergent evolution are
termed analogous structures, in contrast
to homologous structures, which have a common origin
Stabilizing Selection
• Maintains characteristics that are successful for an organism and its
environment – sharks, turtles, and ferns have remained unchanged
for millions of years
• Means that natural selection does not only change the gene
frequencies in a population – it can select against new ones if the a
species is well adapted to its environment and the environment
does not change
• A good classic example of this is human birth weight. Babies of low
weight lose heat more quickly and get ill from infectious disease
more easily, whereas babies of large body weight are more difficult
to deliver through the pelvis.
• Stabilizing selection operates most of the time in most populations.
This type of selection acts to prevent divergence of form and
function.
Homework
• Summarize these notes.