An Ecological Perspective
(BIOL 346)
Talk Three:
Evolution
Evolution
• “Nothing in biology makes sense, except in
the light of evolution”……
– Theodosius Dobzhansky (1973)
• In the U.S. alone, 25 - 40% of Americans
either deny the theory of evolution of think
that evidence for it is lacking.
• Main reason for denying this theory
• Religious Beliefs
Evolution
• Charles Darwin (1809 – 1882) - “on the origin
of species by means of natural selection.”
• The work of Darwin is about adaptation of a
species to the environment in which it exists.
• It does NOT explain the history of the
universe or how the Earth formed.
Evolution
• Charles Darwin (1809 – 1882) - “on the origin of
species by means of natural selection.”
• Had two main hypotheses.
– Branching descent – living species come from a species
that lived in earlier times. This explains common
inheritance.
– Natural selection – explains that parents with genotypes
that favor survival and reproduction leave more offspring
than other parents. Therefore, these genetic traits
become dominant in a given population.
• Both of these hypotheses have been tested
thousands of times without being falsified.
Galapagos Islands
• On the Galapagos Islands
Galapagos Islands Darwin
found a very limited
assortment of animals
• No native mammals or
amphibians were present.
•
Found several species of
large tortoises, a species of
crab-eating lizards, and land
birds
• These birds were made up of
a dozen of closely related
species
Galapagos Islands
• Each cluster of these birds
lived on one or only a few of
these islands.
• The tortoises also differed
from island to island – even
though the climate between
islands was very similar.
• Hypothesized that each
species cluster had arisen
through a series of
modifications from a single
species that had originally
colonized the islands.
Galapagos
Islands
Figure
5.2
Darwin concluded that the
Galapagos had received its
animal colonized from South
America – the nearest
continent from the islands.
Determined that geographical
proximity is more important
than climate or other
environmental variables in
influencing which species
occurred in a particular place.
Natural Selection
•
•
•
•
•
Variation in population
Variation inheritable
Some individuals survive and reproduce
better than others
Survival and reproduction are tied to
variation in traits among individuals (nonrandom)
Therefore, these genetic traits become
dominant in a given population.
Mimicry
• One species of organism
deceptively resembles another.
– The Viceroy is actually closely
related to butterfly A
• The Monarch is poisonous to
Blue jays
• The Viceroy isn’t poisonous,
but has the same colorings as
the Monarch – so Blue jays do
not eat the Viceroys.
Industrial Melanism
• Powerful demonstration
of natural selection.
• Darker colored
peppered moths were
discovered in areas of
the UK with high levels
of pollution.
– Known as melanic moths
• First found in 1890s at
the height of the
industrial revolution.
Remember genetic mutation?
• Either a single nucleotide
substitution or an addition or a
deletion in the genetic
material controlling moth skin
color occurred
– Altered the open reading frame
– May be caused by the pollution
itself
• The result was an ever
increasing population of black
peppered moths in certain
areas.
Central Dogma of Molecular Biology
• DNA holds the code
• DNA makes RNA
• RNA makes Protein
• If pollution altered the
genetic material of
peppered moths, then
the protein product
(skin color) would be
altered!
Industrial Melanism
• Pollution blackened the
trees and killed the lichens
the peppered moths feed on.
– And affected the moths
– Lichen: symbiotic associations
of a fungus with a
photosynthetic partner.
• Moths were camouflaged to
predators and population
increased in polluted areas.
• As I said – A powerful
demonstration of natural
selection.
Industrial Melanism
• Laws to control smokestack
emissions and other forms
of pollutants are now being
enforced.
• The lichens have returned to
the previously polluted
trees.
• Moths in these areas have
returned to their original
colorings
– Again, natural selection
The pattern Figure
of branching
descent.
5.1
Species in the top row are
descended from the ancestors
below.
Red circle – the common ancestor
to all other circles.
Red square - the common ancestor
to all other squares.
Red hexagonal – ancestral to ALL
species
In a classification – all squares in
one group and circles in another
Branching Descent
• Darwin explained this hierarchy as the natural
result of branching descent with modification.
• A process that produces the similarities and
differences that biologists have used in classifying
organisms.
Evidence for Branching Descent
• Homologies: The construction
of family trees in based on
shared similarities and gene
sequences.
• Darwin noted the similarities of
forearms in mammals.
• Darwin wondered on why
mammals have the same bones
in the same relative positions.
• All had a ratio of bones from
five (fingers) to two (lower “arm”
–radius and ulna) to one (upper
“arm” -humerus).
Evidence for Branching Descent
• Convergence – Similarities
that result from common
ancestry should also be similar at
a smaller level of detail.
– Should grow from the same source
tissue
• Convergence is an
evolutionary phenomenon in
which similar adaptations evolve
independently in lineages not
closely related.
• Bat wings are similar in structure
to whale flippers, the human arm
and the front legs of all
mammals.
Evidence for Branching Descent
• One frequent test of the
hypothesis of branching
descent is to identify a group
of organisms that share some
particular character.
•
Structures arose from
modification of the same type
of repeated part.
• Crustaceans mouthparts and
legs are derived from a
common set of leg-like
appendages.
– Vestigial structures –
Structures whose function have
been lost in the course of
evolution diminish in size.
– Ie – coccyx – human tail bone
•
•
Evidence for Branching Descent
Cephalopods - group of
mollusks that have beak-like
jaws at the front of the mouth
and a muscular part (foot)
subdivided into a series of
tentacles.
When these feel threatened
they release “ink” – hides the
animal and propels it backwards
– allows it to escape.
• All members of this group have
the same escape mechanism
– Therefore, same characteristics.
Post - Darwin
• Steven Jay Gould :
• Punctuated Equilibrium – Species remain static for
long periods of time and then changes abruptly.
• The new species begins as a small isolated population on the
geographic periphery of the original species.
•
The small size of the isolated population allows it to
undergo rapid change
– Therefore producing a new species
• Once new species becomes successful, overcomes original
species and the original species becomes extinct.
Hutchinson JR, et al. (2011) From flat foot to fat foot: Structure,
ontogeny, function and evolution of elephant "sixth toes." Science, 334,
1699-1703
•
This CT scan reveals the sixth "toe" here seen in dark green towards the
back on the elephant's foot
•
For more than 300 years, the structure
has puzzled researchers, but this study
suggests that it helps to support
elephants' colossal weight.
•
The structure was made of bone,
although bone with a highly irregular
and unusual arrangement.
•
Closer examination also revealed that it
showed a strong similarity with an
unusual bone that is found in the front
feet of pandas.
Hutchinson JR, et al. (2011) From flat foot to fat foot: Structure,
ontogeny, function and evolution of elephant "sixth toes." Science, 334,
1699-1703
•
This bone - which is not quite an extra
digit, but does the job of one - helps the
panda to grip bamboo, and is called the
panda's "thumb" or "sixth finger".
•
Moles too have a bone masquerading as an
extra digit, which helps them to dig.
•
For elephants, the structure serves a
simple purpose: it helps the hefty animals
to stand up.
•
Unlike pandas and moles, which only have
the false digit in their front feet,
elephants have the bone in all four of their
feet.
Hutchinson JR, et al. (2011) From flat foot to fat foot: Structure,
ontogeny, function and evolution of elephant "sixth toes." Science, 334,
1699-1703
•
Their five conventional toes point
forwards, giving elephants a tip-toed
stance-
•
BUT
– the extra "toe" points backwards into
the heel pad, adding extra support and
helping the heaviest land animal to
hold up its bulk.
•
To find out when and why this strange
bone appeared, the researchers examined
elephant fossils
•
The first elephants appeared around 55
million years ago
Hutchinson JR, et al. (2011) From flat foot to fat foot: Structure,
ontogeny, function and evolution of elephant "sixth toes." Science, 334,
1699-1703
•
Early elephants had a different kind of
foot, which seemed to be quite flat
footed and didn't leave much room for
this structure underneath.
•
The structure seemed to evolved around
40 million years ago, and it seems to
have evolved in concert with elephants
getting bigger and more terrestrial
and having upright feet, with a more
tip-toed foot posture
•
great example of how evolution tinkers
and tweaks tissue to provide different
functions - in this case to be coopted to be used like a digit
Evolutionary diagram showing how elephant foot form
and posture evolved (copyright Julia Molnar, 2011)
Unifying theme in biology
• Underlying the diversity
of life is a striking unity,
especially at the lower
levels of structure.
• Evolution accounts for
this combination of unity
and diversity
– REMEMBER the
universal genetic language
of DNA
Natural selection
Current definition:
Change in genetic composition of a
population over time
Ancestral
population
Time
Envt
Fitness
Divergent
populations
Natural selection
Natural environment “chooses” animals that reproduce
e
Thousands to
millions of years
of natural
selection
Ancestral canine
Artificial selection
Breeder chooses animals that will reproduce
Hundreds to
thousands of
years of
selective
breeding
Ancestral dog
Natural selection
Examples of natural selection and evolution in action
today?
Tuberculosis and
Antibiotic resistance
Using Evolution to understand
HIV AIDS
• Why do drug treatments not work in the long
run?
• Why are some people resistant to HIV?
• Where did HIV come from?
• Will there be an AIDS vaccine?
Why are some AIDS drugs
ineffective now?
• High mutation rate
= Variation
• High reproductive rate
• Mutants that avoid AZT replicate
most
• Natural selection
Why is it so difficult to design an
AIDS vaccine?
• Natural selection
– Mutation
– Variation
– Selection pressures
• Transmission from other hosts
Application of principles of natural selection
creationism
• Bible-based creationists
– Use a biblical account of creation
– Reject any scientific account that conflicts with
scripture
• Intelligent-design creationists
– Work within the framework of science to find
evidence of design in nature
– State that biological systems are so complex that only
an intelligent (and benevolent) designer could have
made them.
• Theistic evolutionists
– Believe that God created the universe and all life
– Evolution is in fact Gods creative process and part of
the plan.
Misconceptions
• Scientists disagree about whether evolution
has occurred
Scientists argue about HOW evolution occurs but they
agree that evolution does occur.
Misconceptions
Evolution as a theory is incomplete or flawed.
Evolution is the only well-supported explanation for the
diversity of life and there have been no credible
challenges to evolution.
Modifications to some of Darwin’s original ideas have
changed e.g., evolution occurs faster, genetic mutations
are sources of variation
Misconceptions
• If you accept evolution, you cannot be a
religious person
•Evolution and religion are not incompatible.
•Most Christian and Jewish religions have no problem
with evolution.
•Many religions believe that a better understanding of
the natural world enriches one’s faith.
•Not all scientists are atheists.
I’m cool
with
Theistic
Evolution
Summary
• Must understand the nature of science to
understand evolution.
• Evolution does occur and is observable.
• Natural selection can happen over short time
periods.
• Study of evolution is important and
applicable to medicine and many other
disciplines.
The End.
Any Questions?