Continuity of Life on Earth

Continuity of life on Earth
Sarah Jones
designapplause.com

Life has existed on Earth for approximately 3.5
billion years …
greenforecast.com

The processes that have transformed life on
Earth from its earliest forms to the vast
diversity that characterises it today…
Evolution
www.fromquarkstoquasars.com
http://slideplayer.com/user/2995729/

Dawkins, 2011
… a change in the genes.

Dawkins, 2011
“Through the process of
descent with modification,
the common ancestor of life
on Earth gave rise to the
fantastic diversity that we
see documented in the
fossil record and around us
today. Evolution means that
we're all distant cousins:
humans and oak trees,
hummingbirds and whales.”
(evolution.berkeley.edu,
2016)

Old Theories of Evolution
• Jean-Baptiste Lamarck (early 1800’s)
proposed:
“The inheritance of acquired characteristics”
• He proposed that by using or not using its
body parts, an individual tends to develop
certain characteristics, which it passes on to
its offspring.
www.linkmesh2.com

Lamarck believed that:
A giraffe acquired its long neck because its
ancestor stretched higher and higher into the
trees to reach leaves, and that the animal’s
increasingly lengthened neck was passed on to
its offspring.
www.thewallpapers.org

H.M.S. Beagle (1831-1836)
en.wikipedia.org

• Darwin set sail on the H.M.S. Beagle (1831-
1836) to survey the south seas (mainly South
America and the Galapagos Islands) to collect
plants and animals.
• On the Galapagos Islands, Darwin observed
species that lived no where else in the world.
www.bbc.co.uk

“As many more individuals of each species are
born than can possible survive, and as,
consequently, there is a frequently recurring
struggle for existence, it follows that any being, if
it vary however slightly in any manner profitable
to itself, under the complex and sometimes
varying conditions of life, will have a better
chance of surviving and thus be naturally
selected. From the strong principle of inheritance
any selected variety will tend to propagate its
new and modified form.” Charles Darwin

• Written in 1859 “On the Origin of Species by
Means of Natural Selection”
• Two main points:
– Species were not created in their present
form, but evolved from ancestral species.
– Proposed a mechanism for evolution -
Natural Selection.
www.huffingtonpost.com

Darwin’s Five Points
1. A population has variations.
2. Some variations are favourable.
3. More offspring are produced than survive.
4. Those that survive have favourable traits.
5. A population will change over time.

Natural Selection
Individuals with favourable traits are more
likely to leave more offspring better suited for
their environment.
www.flutterbyinfo.com

Variation
• Natural selection happens because there is
variation i.e. natural differences in
populations.
• Variation is caused by differences in genes.
http://www.darwinwasright.org/genetics.html

Speciation
• When one species splits into two or more
separate species.
• Speciation is why we see biodiversity on Earth.
• Steps of speciation
1. Variation
2. Isolation
3. Selection
www.thinglink.com

• Variation – within a populations is required
before speciation can occur.
• Isolation – required for a new species to occur
e.g. Grand Canyon ground squirrel.
• Selection – natural selection affects genotype.
Changes prevent groups from breeding in the
future.
www.wunderground.com

Sexual Selection
www.hd-wallpapersdownload.com

Artificial Selection
• The selective breeding of domesticated plants
and animals by man.
• The ancestor of the domesticated dog is the
wolf.
healthypets.royalcanin.com.au

Evidence For Evolution
www.philpoteducation.com

Palaeontology
• The study of fossils — any form of preserved
remains thought to be derived from a living
organism.
• Fossils are an important source of evidence
for evolution.
observationdeck.kinja.com

Evidence From Fossils
• The lowest rock layers are usually the oldest.
• The oldest rock layers contain the oldest fossils.
• The rock layers that formed later contain more
complex kinds of organisms.
• The variety of fossils increases in the upper,
more recent layers of rock.
• No fossil records exist of modern, living plants
and animals.

http://www.detectingdesign.com/fossilrecord.html

Relative Age - Relative means that we can
determine if something is younger than or older
than something else. Relative time does not tell
us how old something is, all we know is the
sequence of events.
en.wikibooks.org

Absolute Age - Absolute age means that we can
more or less precisely assign a number (in years,
minutes or seconds) to the amount of time that
has passed. We can say how old something is.
www.mrgoodenough.com

Correlation
Early fossil examiners were able to correlate or
match layers of sedimentary rock merely by
looking at the fossils they contained (fossils in a
particular rock were different from rocks above
and below).
higheredbcs.wiley.com

Some plant and animals only lived a short
time in geological history, yet had a wide
spread distribution. Known as index fossils –
used to correlate layers of rock and therefore
determine the age of the layer.

Limitations of fossils
There are many gaps in the fossil record. This is
because:
– dead organisms decompose rapidly.
– dead organisms are eaten by scavengers.
– soft-bodied organisms do not fossilise easily.
– only a small fraction of organisms die in
conditions favourable to fossilisation.
– only a fraction of the fossils have been
unearthed.

Geophysical evidence suggests that
geographical regions and climatic conditions
have varied throughout the earth’s history, and
these changes would have favoured a
mechanism for evolutionary change.
science.psu.edu

Ecological considerations also support this.
Plants appeared on land before animals, and
insects before insect-pollinated plants.
tx.english-ch.com

Biogeography
• Distribution gives clues to the evolutionary
history of organisms and of the Earth itself.
• A major cause of speciation in most groups is
thought to be geographic fragmentation of
ancestral species e.g. continental drift and
consequent isolation of populations.
www.animalpicturesociety.com

Comparative Anatomy
• Comparative anatomy is the study of similarities
and differences in the anatomy of organisms.
• Two major concepts of comparative anatomy
are:
www.ib.bioninja.com.au
Homologous and Analogous Structures

Homologous Structures
• Those that are similar in structure and
development but which may have different
functions.
• The wing of a bird, the flipper of a whale and
the leg of a dog all possess the structural plan
of the pentadactyl (5-digit) limb although their
functions differ.

• Homology, therefore, implies common
ancestral origins and suggests that
differences in structure have evolved in
response to different environmental
conditions.
• This is called divergent evolution.

Analogous Structures
• Analogous structures have a similar function but
no structural relationship. The wing of an insect
and the wing of a bird serve the same function
— flight — but are structurally dissimilar.
• This suggests that these two groups have
different ancestral origins.
www.vce.bioninja.com.au

These structures are regarded as examples of
convergent evolution, whereby structures
with different origins have become adapted to
a common function.

www.hbjzds.com hdwallpaperbackgrounds.net
voices.nationalgeographic.com onehdwallpaper.com

• Parallel evolution occurs when related
species evolve similar features
independently.
• For example, within eucalyptus, a number of
species have evolved a white, waxy coating
on their leaves, which protects them from
frost damage at high altitudes or from water
loss in dry conditions.

Vestigial Organs
An organ that was once useful in an animal’s
evolutionary past, but now has no apparent
nor predictable function e.g. rudiments of
pelvis and hind limbs in snakes, wings on many
flightless birds.
smithlhhsb122.wikispaces.com

Transitional Fossils
Archaeopteryx
www.flickr.com

Molecular Biology
DNA and proteins (amino acids) – sequencing of
DNA and proteins indicates the degree of
relatedness between organisms.

Hardy-Weinberg Principle
The concept that the shuffling of genes that
occur during sexual reproduction, by itself,
cannot change the overall genetic makeup of a
population.
www.thealevelbiologist.co.uk

The Hardy-Weinberg Principle will be
maintained in nature if all five of the following
conditions are met:
1. Large population
2. Isolation = no migration
3. No net mutations
4. Random mating
5. No natural selection
If these conditions are
met, the population is at
equilibrium.
Therefore, “No Change”
or “No Evolution”.

Macroevolution
The origin of taxonomic groups higher than the
species level.
www.evogeneao.com

Microevolution
• A change in a population’s gene pool over a
succession of generations.
• Evolutionary changes in species over relatively
brief periods of geological time.
www.nydailynews.com

Five Mechanisms of Microevolution
1. Genetic drift:
Change in the gene pool of a small
population due to chance.
Two examples:
a. Bottleneck effect
b. Founder effect slideplayer.com

a. Bottleneck Effect
Genetic drift (reduction of alleles in a population)
resulting from a disaster that drastically reduces
population size.
Examples:
1. Earthquakes
2. Volcano’s
http://biologyasifitmattered.blogspot.com.au

b. Founder Effect
• Genetic drift resulting from the colonization of
a new location by a small number of
individuals.
• Results in random change of the gene pool.
Example:
Islands (Darwin finch)

2. Gene Flow:
The gain or loss of alleles from a population
by the movement of individuals or gametes.
• Immigration or emigration.

3. Mutation:
Change in an organism’s DNA that creates a new
allele.
4. Non-random mating:
The selection of mates other than by chance.
5. Natural selection:
Differential reproduction.
www.audubon.org

Speciation
The evolution of new species.
phys.org

Reproductive Barriers
Any mechanism that impedes two species from
producing fertile and/or viable hybrid offspring.
Two barriers:
1. Pre-zygotic barriers
2. Post-zygotic barriers
www.1millionfreepictures.com

1.Pre-zygotic Barriers
a. Temporal isolation:
Breeding occurs at different times for different
species.
b. Habitat isolation:
Species breed in different habitats.
c. Behavioral isolation:
Little or no sexual attraction between species.

d. Mechanical isolation:
Structural differences prevent gamete
exchange.
e. Gametic isolation:
Gametes die before uniting with gametes
of other species, or gametes fail to unite.
www.studyblue.com

2.Post-zygotic Barriers
a. Hybrid inviability:
Hybrid zygotes fail to develop or fail to reach
sexual maturity.
b. Hybrid sterility:
Hybrid fails to produce
functional gametes.
c. Hybrid breakdown:
Offspring of hybrids are weak or infertile.
www.1millionfreepictures.com

Allopatric Speciation
Induced when the ancestral population
becomes separated by a geographical barrier.
Example:
Grand Canyon and ground squirrels
www.thinglink.com

Adaptive Radiation
Emergence of numerous species from a common
ancestor introduced to new and diverse
environments.
Example:
Darwin’s Finches

Sympatric Speciation
Result of a radical change in the genome that
produces a reproductively isolated sub-
population within the parent population (rare).

Interpretations of Speciation
Two theories:
1. Gradualist Model (Neo-Darwinian):
Slow changes in species overtime.
2. Punctuated Equilibrium:
Evolution occurs in spurts of relatively
rapid change.

Coevolution
Evolutionary change, in which one species act as
a selective force on a second species, inducing
adaptations that in turn act as selective force on
the first species.
Example:
1. Acacia ants and acacia trees
2. Humming birds and plants with flowers
with long tubes
www.audubon.org

Extinction
Populations with reduced genetic diversity face
increased risk of extinction.
all4desktop.com

There was no first human…
Dawkins, 2011

Reference
Clarence Cockett, Slideplayer,
http://slideplayer.com/user/2995729/, 2016
All other links on relevant slides and images.

Continuity of Life on Earth

Continuity of Life on Earth

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