Evolution
(chapter 5)
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.
Evolution explains the
origin of a species
NOT
The origins of life
Evolution
• How is the origin of species
different from the origins of life?
Origin of Life
• The Primitive Earth.
– Theorized early primitive atmosphere consisted mostly
of:
• water vapor, nitrogen, and carbon dioxide, with small
amounts of hydrogen and carbon monoxide.
• Little, if any, free oxygen
• At first the earth was very hot
• Water existed as a gas
Origin of Life
Origin of Life
Origin of Life
Origin of Life
• Small Organic Molecules.
– Primitive gases may have reacted with one another
and produced small organic compounds such as
nucleotides and amino acids.
• Macromolecules.
– RNA-first hypothesis.
– Protein-first hypothesis.
RNA-first Hypothesis
• Only RNA is needed to progress towards the first
cells
• RNA is both a substrate and an enzyme (ribozymes)
– First cell had RNA genes (mRNA) – make proteins
• Some of these newly formed proteins were enzymes
• Reverse transcriptase (found in retrovirus)
• Can make DNA from RNA
• DNA self replication can then occur
Protein-first hypothesis
• Amino acids join together under dry heat
– Such as along shallow puddles on a rocky shore.
– Heat from sun formed proteinoids (enzymes)
• These then could form DNA from nucleotides
present in the ocean.
• This DNA can code for specific protein synthesis
– Thus the cell could acquire of its enzymes, even the
ones which replicates DNA
Origin of Life
• Protocell.
– A protocell, which could carry on metabolism but
not reproduce, may have formed when lipids and
microspheres formed a lipid-protein membrane.
• A True Cell.
– A true cell can reproduce.
• Modern cells replicate before cell division occurs.
Biological Evolution
• First true cells were prokaryotic.
– Eukaryotic cells evolved later, followed by the
other kingdoms.
• Biological evolution is a change in life forms
that has taken place in the past and will take
place in the future.
–Adaptation is a characteristic that makes an
organism able to survive and reproduce in
an environment.
Evolution, based on the
hypotheses of Darwin, has
nothing to do with the theory
of the creation of the Earth.
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 (non-random)
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 of branching
Figure
5.1
descent.
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 tiptoed foot posture
•
great example of how evolution tinkers
and tweaks tissue to provide different
functions - in this case to be co-opted
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
Time
Ancestral
population
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 are some people
resistant to HIV?
• Mutant forms of molecule that assists
the virus entry into cells
• Primarily in European populations;
none in Asian or African populations
Where did AIDS come from?
HIV phylogeny
• Examine similarity
in DNA sequence
• HIV was
transmitted from
chimps to humans
3 different times
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.
Interested?
• Kenneth Miller. 1999. Finding Darwin’s God:
a Scientist’s Search for Common Ground
between God and Evolution
• Pennock, Tower of Babel (intel design)
The End.
Any Questions?