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Evolution
part 2
Made just for You by:
The Biology 1 Science Team
International School Bangkok
Evolution and Natural Selection
• What do we mean when we say that life on Earth
has evolved and is evolving?
– Living things change over time, in shape, size,
behavior, etc. and in their DNA code.
– Evidence also suggests that one species can give rise
to multiple new species, and that all living things
today share a common ancestor
• What is the alternative possibility?
– Living things have not changed over time. Their
shape, size, behavior etc. and DNA has always been
the same. Species do not share ancestor species.
Let’s look at the evidence!
Evidence relating to Evolution
by Natural Selection*
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•
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•
•
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Artificial Selection
Fossils
Biogeography
Embryology
Vestigial Features
Homology and Analogy
Biochemistry
Observed examples
*These represent just SOME of
the lines of evidence that
support evolution by natural
selection and this course only
addresses them at a basic level.
Artificial Selection
Instead of the natural environment leading to differences in
survival and reproduction, humans can artificially select for
different traits.
Is there actually
enough variation to
make members of the
same species look
really different?
What should we expect if
life has evolved?
If it has not evolved?
Dogs diverged from wolf ancestors
thousands of years ago but most modern
dog breeds are only a few hundred years
old. Size, color, loyalty, hunting behaviors,
body shape, etc. have been selected for.
Artificial selection in Brassicas
Evidence For Evolution: FOSSILS
• Traces of pre-historic living things.
What should we expect if life has evolved?
If it has not evolved?
Fossil analysis
Fossil record extends back billions of years 
1. The fossil record (millions have been analyzed)
is 100% consistent with ordered change over
time; the oldest forms being most unlike more
recent / modern forms.
2. Many fossils are transitional, with
characteristics in between earlier and later
group known groups.
3. Many fossils are unlike any existing organisms.
4. Zero authenticated fossils have been found
outside the time range predicted by evolution.
Is this what we would expect if life has evolved,
or if it has not? Why?
Orderly change: oldest fossils
most unlike recent.
• What trends (orderly changes) can
you see in these hominid skulls?
– Increasing brain size
– Flattening of face
– Drecreasing brow ridges
Evidence For Evolution: Fossils!
Transitions:
How is Archaeopteryx
like a reptile? How is it like a bird?
Fossil Analysis
Scientists have often predicted transitional forms,
and later such forms have been discovered.
Darwin hypothesized that mammals evolved on land, therefore water mammals
like seals must have evolved from land animals. He predicted a fossil intermediate
between land mammals and seals.
Seal
Puijila: a “walking seal”, fossil discovered 2007
Fossil analysis
• We do not find fossils “out of order”.
J.B.S. Haldane,
when asked what
hypothetical
evidence could
disprove evolution,
replied "fossil
rabbits in the
Precambrian era"
Biogeography
What species live in different places around the
world?
Let’s suppose there are two ponds on different continents with
the same climate and conditions. Will the species living there be
the same? Or will the species be different, but related to nearby
species?
What
should we
expect if life
has
evolved?
If it has not
The Wallace Line – in native species, placental mammals
dominate to west, marsupials to the east. An example of
biogeographical variation.
Mammals
• Placentals and
marsupials are
fundamentally different
in structure
• However, in a large
ecosystem with similar
niches, similar traits are
helpful
• Similar features are seen
in animals with similar
niches
• Ex. The placental wolf is
more closely related to
the placental mouse (or
any placental) than to
the Tansmanian Wolf (or
any marsupial).
Embryology
All sexually reproduced
animals begin as a single
cell, and must begin
developing from there.
What should we expect if
life has evolved?
If it has not evolved?
Not the similarities at early stages, with increasing differences.
Note the early formation of GILL SLITS in vertebrate embryos.
Note the post-anal TAIL in human embryos.
The early embryonic stages of the (a) lemur, (b) pig,
and (c) human.
Vestigial Structures
Left-over structures that
were useful in ancestor
species, but no longer
serve any function in the
modern organism
What should we expect if
life has evolved?
If it has not evolved?
The (a) salamander and (b) whale, inherited hind
limb bones from a common ancestor; the bones
remain functional in the salamander but are vestigial
in the whale.
Homology:
A shared underlying structure modified to
different purposes.
What should we expect if life has evolved?
If it has not evolved?
ANALOGY
 Fundamentally different structures that look
similar because they serve a similar function.
What should we expect if life has evolved?
If it has not evolved?
Even true in flying (gliding) fish.
The wings are modified gills!
Let’s take the example of
flight (or gliding).
What features would be
useful?
• Large flat surface
• Brace / support system
Understanding check: What is ANALAGOUS in this picture? What is HOMOLOGOUS?
Biochemical Evidence
The chemistry of life is controlled by
DNA. DNA codes for proteins, and
protein perform most functions in the
cells.
What should we expect if life has evolved,
especially from a common ancestor?
If it has not evolved?
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•
•
The code from DNA to protein is UNIVERSAL the same in every
species (always triplets of bases, always the same 20 amino acids
to build proteins)
No matter what they look like, species that share a more recent
ancestor will have more similar sequences of DNA
The genes will be similar, with “gene families” showing various
degrees of mutation, and inactivated genes
DNA Code is Universal
• The “code” for DNA to protein is universal – we can
even make genes from one species work in
another!
Similar Sequences of DNA:
How Closely Does Our DNA Compare to Another Human?
All humans have the same genes, but some of these genes contain
sequence differences that make each person unique. With these
variations the DNA between 2 Humans is 99.9% similar.
Similar Sequences of DNA
A chimpanzee? 98% - Chimpanzees are
the closest living species to humans.
Similar Sequences of DNA
A mouse? 92% - All mammals are
quite similar genetically.
Fruit Fly? 44% - Studies of fruit
flies have shown how shared
genes govern the growth and
structure of both insects and
mammals.
DNA and Evolution
Yeast? 26% - Yeasts are single-celled organisms, but they have many
housekeeping genes that are the same as the genes in humans,
such as those that enable energy to be derived from the breakdown
of sugars.
DNA and Evolution
A weed (thale cress) 18% - Plants
have many metabolic differences
from humans. For example, they
use sunlight to convert carbon
dioxide gas to sugars. But they also
have similarities in their
housekeeping genes.
Biochemistry
• Duplicated genes often have related functions
but also evolve differences.
Observed Evolution
• Significant genetic change
over time usually takes
longer than a human
lifetime to observe,
however there are many
exceptions.
• Ex. Anolis lizards colonized
14 Caribbean islands which
previously has no lizards.
Over 20 years, marked
diversification occurred in
size, color, diet, and
behavior. It appears than
new species may even
have developed.
OBSERVED EVOLUTION and
DOES IT MATTER IF PEOPLE UNDERSTAND EVOLUTION?
What do you do if you get a bacterial infection, like an infected cut,
or a cough that gets worse, or a UTI, or strep throat?
Often you take ANTIBIOTICS, special drugs that cause death in bacterial
cells.
Antibiotics were first widely used in 1945 and more types have been
developed. Antibiotics have saved many millions of lives. By the 1970s
there were antibiotics effective against almost all types of diseasecausing bacteria!
What next? When should we use antibiotics? Do we need more
research, or should we focus on solving other problems? Is our “bacteria
problem” solved?
Discuss.
I do NOT understand evolution
/ natural selection!
I understand evolution and
natural selection!
We have figured out how
to defeat bacteria. Game
over, we win! We can use
our antibiotics as much as
we want, on animals and
plants as well as humans.
We don’t need to spend
money researching new
antibiotics since we
already have all we need.
Antibiotics are a change in
the environment, and any
mutation that helps
bacteria survive antibiotics
will increase through
natural selection. Over
time, resistance will evolve.
We are ahead, but the war
will never be over. We need
to use antibiotics sparingly
and carefully. We need to
continue research into new
drugs.
MRSA: methicillin-resistant Staphylococcus aureus:
A bacteria that causes life-threatening infections
Resistance in Neisseria gonorrhoeae
10
8
% Resistant Strains
E. Coli
6
4
2
0
1980
1982
1984
1986
1988
1990
• What could this mean?
– People begin to die from
infections that we could
easily have cured a few
years ago
• What can we do?
– Take antibiotics as
directed
– Limit antibiotic use for
non—medical uses (in
hand soap, livestock and
crops)
– Give antibiotics only
when needed for
bacterial infections
Why would the directions above help limit
evolution of antibiotic resistance?
Other Vocabulary for EVOLUTION:
• CONVERGENT evolution leads to Analogous Features
• DIVERGENT evolution leads to Homologous Features
• SPECIATION in the emergence of new species from
an older species
CONVERGENT EVOLUTION:
Let’s take the example of predators in a
watery environment.
What traits would be successful?
Lots of teeth!
A big powerful tail!
A streamlined shape – like a torpedo!
Short, stubby fins for agile maneuvering but
little drag!
Darker color above than below to help
approach prey!
Sounds like a shark, doesn’t it!
Or a dolphin.
Or a Northern Pike.
Or a Barracuda.
Or even a Penguin!
Same Problems, Similar Solutions, Different Origins!
REMEMBER – this
is called
CONVERGENT
EVOLUTION
SPECIATION – AN EXAMPLE
When there is GEOGRAPHIC ISOLATION between
populations, they will evolve differently.
They do NOT share the same gene pool!
This cat-sized camel ancestor migrated
throughout the world during the past ice age.
Old World
New World
They crossed the Beringia land bridge!
Their isolation has led to today’s relatives.
An “Old” World Camel, the BACTRIAN CAMEL.
The DROMEDARY CAMEL, another Old World example.
The Llama: A “New” World Camel
MORE NEW WORLD CAMELS
Vicuna
Alpaca
. . . and another, the Guanaco
Kaibab squirrel on
The north rim.
Abert’s lives on the
south rim.
Another speciation case – Abert’s squirrel and the
Kaibab squirrel. Reproductive isolation caused by
the Grand Canyon has formed these 2 species.
DIVERGENT EVOLUTION: From the same starting
point, features are modified to different ends.
REMEMBER – this
is called
DIVERGENT
EVOLUTION
Look at the range of beak sizes and shapes evolved
for different functions in the finches of the
Galapagos Islands.