Evolution: Changes
Over Time
Chapter 14
Evolution: History Of Ideas
 Over time many ideas have been proposed in order to
account for the biodiversity that resides on Earth.
 Some of these ideas were strange:
 For example in the 1700’s Benoit De Millet described that
the appearance of birds was due to flying fish being
chased out of the water.
 As time went on, our ideas of evolution have changed
and evolved.
Nineteenth-century Views
 In the 19th Century, there were three main individuals
which have influenced our ideas of evolution
significantly:
 Erasmus Darwin
 Jean Baptiste Lamarck
 Robert Chambers
Erasmus Darwin (1731-1802)
 Erasmus Darwin was the grandfather of
Charles Darwin.
 He was a physician, a well known poet,
philosopher, botanist, and naturalist.
 He was the one who initially came up with
the ideas on evolution that Charles later
elaborated on.
 Erasmus argued that all organisms on Earth
originated from a common ancestor.
Jean Baptiste Lamarck
(1744 – 1829)
• Lamarck thought that if an
animal acquired a
characteristic during its
lifetime, it could pass it
onto its offspring.
• Hence giraffes got their
long necks through
generations of straining to
reach high branches.
Robert Chambers
(1802 – 1871)
 Was a supporter of the idea of evolution.
 In 1844, he anonymously published a book outlining
his ideas on evolution, Vestiges of the Natural History
of Creation.
 Chambers’ main idea on evolution was that over a
period of time, species had the capability of changing
in order to better suit their environment
Species: Unchanging or Not?
 Through most of the 1800s scientists believed that
species cannot change and they were fixed, as they
had been since their creation.
 Creationism was viewed as the only means by which
different organisms on Earth existed.
Charles Darwin (1809-1882) and
Alfred Russel Wallace (1823-1913)
• During a five year voyage on the HMS Beagle, Darwin was
introduced to biological diversity all over the world.
• He gathered specimens that he eventually used as support for
his theory of natural selection.
• He proposed that random genetic variations exist in
populations that allow some individuals to produce more viable
offspring, changing the population.
• Darwin worked closely with Wallace who was another
naturalist at the time that had come to the same conclusions
as Darwin, but without the extensive evidence that Darwin
had.
The Darwin-Wallace view
 As Darwin and Wallace had come to the same
conclusions regarding evolution, they decided to
publish their ideas together in a joint publication.
 Wallace and Darwin published their works on natural
selection in 1859 together. This publication was 20
years after Darwin first drafted Origin of the Species
and sent it to other colleagues to review.
 Evolution, or change over time, is the process by
which modern organisms have descended from ancient
organisms.
Neo-Darwinism
 Neo-Darwinism is a term used to describe the
'modern synthesis' of Darwinian evolution through
natural selection with Mendelian genetics.
 Although Darwin and Mendel had hypothesised about
their respective ideas about Evolution and genetics
around the same time, neither knew of the other’s
work.
 Today, it is hard to imagine studying Evolution without
having studied Mendelian genetics.
Social and Political Influences on
Theories of Evolution
 The reason why it took Darwin such a long time to
publish his theories was because it may not have been
received well by the scientists at the time.
 Many scientists held the teachings of the church as
sacred, and Darwin did not want to be against the
church
 Darwin also did not know what the general reaction to
his ideas would be.
Time Scales in Evolution
 The study of time scales is integral to the study of
evolution.
 By studying time scales it makes it possible to study
the age of fossils and rocks and also to estimate the
age of the Earth itself.
Estimating the Age of the
Earth
 Up until the mid-1800s, it was thought that the Earth was
only about 6,000 years old. This date was derived by
Archbishop James Ussher in the 1600s from the Bible.
 It is thought that the actual age of the Earth is 4.54 billion
years old.
 This makes much more sense to scientists as it provides the
time frame over which evolution has had a chance to occur.
 The age of the Earth is measured by using radiometric
techniques on the oldest known meteorites on Earth.
Geologic Time
• This time scale was developed in
the nineteenth century when
geologists observed that particular
rocks where characterised by
distinctive groups of fossils.
• Names were based on areas
where they were first recognised
or on the distinctive nature of the
rocks.
• For convenience the geological
time scale divided the Earth’s
history into hierarchical intervals.
The most widely used time
intervals are Periods.
• The time interval predating the
appearance of the first abundant
fossils is called the Precambrian.
How old is it?
 The difference between absolute and relative age:
 Absolute age is the actual age of something. For example
7 years old.
 Relative age is a comparison of ages. For example object
A is 12 years older than object B.
 In studying evolution, we use both absolute and
relative dating in order to figure out the age of fossils
and rocks.
Relative Age
 When we look at layers of different types of rocks in
the Earth’s crust, we are looking at relative age.
 For example if we find a fossil above a certain layer of
rock, we can conclude that the fossil is younger than
that layer of rock.
Absolute Age
 In order to find the absolute age of rocks, we use
radiometric dating.
 This is based on the rate of decay of radioactive
elements which are present in rocks.
 We use the half lives of these elements in order to
backtrack and find out when the rock was originally
formed.
 There are many different elements that we can use in
order to determine absolute age.
Potassium-Argon (K-Ar)
Dating
 The Potassium-Argon (K-Ar) dating method is the
measurement of the accumulation of argon in a
mineral.
 This method works by using the radioactive from of
Potassium (K40), whose half life is around 1,250 million
years.
 The decay of K40 yields Ar40 and Ca40.
 So this method works by counting the amount of Ar40.
Argon39/Argon40 Dating
 This technique is similar to the K-Ar dating technique.
 In this type of dating, the object to be tested is
irradiated in order to convert the K39 to Ar39.
 The amounts of Argon are then measured and hence
an age can be estimated.
Carbon14 Dating
 This dating technique also works in the same as the
previous techniques we have discussed (using the halflife of the isotope).
 As the half-life of carbon14 is a lot shorter than any of
the other dating techniques (5,740 years), it cannot
date things which are too old.
 This dating method is used to date things which are up
to about 60,000 years old.
Electron Spin Resonance
 This technique is mostly used to date minerals.
 It works by using radiation to cause electrons to separate
from the atoms.
 These electrons then become trapped in the crystal lattice of
minerals.
 This changes the magnetic field of the material at a rate
that is predictable, allowing it to be used to date an item.
 It can be used to date when mineralisation, sedimentation,
or the last heating of minerals took place.
Evidence of Evolution
 The evidence of evolution lies in many aspects that
have been studied in biology.
 This includes:

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The Fossil Record
Comparative anatomy
Homology and Analogy
Embryology
The Fossil Record
© NASA
origins
bacteria
complex cells
dinosaurs
humans
The fossil record shows a sequence from simple bacteria to more
complicated organisms through time and provides the most compelling
evidence for evolution.
Transitional fossils
• Many fossils show a clear transition
from one species or group to
another.
• Archaeopteryx was found in
Germany in 1861. It shares many
characteristics with both dinosaurs
and birds.
• It provides good evidence that
birds arose from dinosaur
ancestors
Archaeopteryx
Comparative Anatomy
• Similar comparisons can be
made based on anatomical
evidence.
• The skeleton of humans and
gorillas are very similar
suggesting they shared a recent
common ancestor, but very
different from the more
distantly related woodlouse…
Human and Gorilla
Woodlouse
Homology: Similar Structures
Analogy: Similar Function
 Analogous structures
do not derive from the
same ancestral
structures, but serve a
similar or same
purpose.
Vestigial Structures and Organs
• As evolution progresses, some
structures are no longer useful to an
organism.
• These are known as vestigial
structures.
• The coccyx is a reduced version of
an ancestral tail, which was adapted
to aid balance and climbing.
• Another vestigial structure in
humans is the appendix.
The coccyx is a vestigial tail
Comparing Embryos
Comparative biochemical and
genetic studies
 If organisms are close relatives of one another, then it
is true that they would share a high degree of genetic
and chemical similarities.
Comparing proteins
 All proteins are built from the 20 different amino acids.
 Proteins from different species can be compared, and
the similarities and differences in the amino acid
sequence can be studied.
Comparing DNA by
hybridisation
 Another comparing technique is DNA hybridisation to compare
how similar two strands of DNA are.
 In this technique, DNA is heated until the two strands separate.
This is done for both species to be compared.
 These separated strands are then mixed and let to cool.
 Once the DNA strands cool, down, they have a tendency to pair
up again.
 At this stage, a DNA strand from one species would be pairing
with the DNA from another.
 Hybridised sequences with a high degree of similarity will bind
more firmly, and require more energy to separate them: i.e.
they separate when heated at a higher temperature than
sequences which share less similarities,
Comparing DNA: Gene
Sequences
 Comparing gene sequences is an automated,
computer-based examination of DNA in order to reveal
genetic or evolutionary relationships between
organisms.
Comparing Chromosomes
Involves comparing
chromosomes and their
banding patterns. (H =
human, C = chimpanzee
Bio-geographic Distributions
 Another way we can compare organisms is by their biogeographic distributions.
 For example, when Charles Darwin visited Australia, he
noticed that there were no rabbits even though that
the conditions seemed perfect for them.
The ‘molecular clock’ concept
 The molecular is a technique that uses rates of
molecular change to find the time in geologic history
when two species diverged.
 It is used to estimate the time of occurrence of events
called speciation.
Calibrating and testing the
‘clock’
 In order to calibrate the clock, the absolute time of a
speciation event must be known.
Molecular Clock
Observations about amino acid changes that occurred during the
divergence between species show that molecular evolution takes
place at an approximately constant rate. Further evidence for this
came from the relative rate test. This suggests that molecular
evolution is constant enough to provide a molecular clock of
evolution. This means that the amount of molecular change between
two species measures how long ago they shared a common ancestor.
Molecular differences between species are therefore used to infer
phylogenetic relations.
Molecular evolution in living fossils provides an example of a constant
rate of molecular evolution independent from morphologic evolution.
Figure: the constant rate of evolution of the alpha-globin. Each point
on the graph is for a pair of species, or groups of species.
Figure: the constant rate of evolution of the alpha-globin. Each point on
the graph is for a pair of species, or groups of species.
Patterns of evolution
 There are many different patterns of evolution. These
include:
 Divergent evolution
 Convergent evolution
 Parallel evolution
 Co-evolution
Divergent Evolution
 Divergent evolution is the accumulation of
differences between groups which can lead to the
formation of new species.
 Usually this happens as a result of the same species
adapting to different environments, leading to natural
selection defining the success of specific mutations.
Convergent Evolution
 Convergent evolution describes the acquisition of
the same biological trait in unrelated lineages.
Parallel Evolution
 Parallel evolution is the development of a similar
trait in related, but distinct, species descending from
the same ancestor, but from different clades.
Co-Evolution
 In a broad sense, biological co-evolution is "the
change of a biological object triggered by the change
of a related object". Co-evolution can occur at multiple
levels of biology: it can be as microscopic as correlated
mutations between amino acids in a protein, or as
macroscopic as traits between different species in an
environment.
Speciation
 Speciation is the evolutionary process by which new
biological species arise.
Evolution: Gradual or
Intermittent?
 There has been continual debate in the scientific
community about whether evolution is gradual or
intermittent (also known as punctuated).
 Gradual evolution refers to the gradual change of
organisms over a period of time.
 Intermittent evolution refers to the sudden change in
organisms
Punctuated Equilibrium
An interesting example:
flounder