1. EVOLUTION AND
FIXITY
© 2008 Paul Billiet ODWS

2. Evolution
 The process of cumulative change in the
heritable characteristics of a population
Fixity
 The creation of life followed by no further change
© 2008 Paul Billiet ODWS

3. The Greek Philosophers
 Aristotle developed an idea of the
organisation of life through a ladder of
life (Scala Natura) and that this
organisation was fixed
 Other Greek philosophers, such as
Diogenes, thought that life evolved
© 2008 Paul Billiet ODWS

4. The Biblical interpretation
 Literal interpretations of the Bible
suggested that the Earth was only
a few thousand years old
 This short time span seemed
appropriate for creation of life by a
divinity followed by fixity
Archbishop Ussher
1580-1656
© 2008 Paul Billiet ODWS

5. Intelligent design
William Paley (1802)
Developed the idea of
intelligent design through
special creation
 Living organisms were too
complex and well adapted
to have evolved by chance
 Their complexity was the
sign of a creator The Dalvey Depot
© 2008 Paul Billiet ODWS

6. Time to evolve
The development of ideas in
geology
Starting in the 17th
century studies
in geology pushed back the
estimated age of the Earth from
thousands to millions of years
 Time for evolution to occur was
now available
 Fossils of animals and plants no
longer found on Earth, were
discovered in strata
 They are similar to those alive
today
BSAC Travel Club
Ammonite
© 2008 Paul Billiet ODWS

7. Catastrophism
 Advocates of special
creation explained fossils
in terms of the victims of
natural (biblical)
catastrophes
 (e.g. Noah’s Flood)
 Those that did not
survived the flood were
the fossils of creatures
that do not exist today
Georges Cuvier 1769 – 1832
Public Domain Image
© 2008 Paul Billiet ODWS

8. Radioactivity
 Estimates on the age of the Earth were
made from experiments in cooling,
observations of sediments and the salinity of
the seas
 Absolute dating for rocks came with the
discovery of radioactivity and radioisotopes
 This revealed fossils to be millions or even
billions of years old
© 2008 Paul Billiet ODWS

9. Systematics
 Collections of animals and
plants in museums
increased from 17th
century
 The need for systematic
classification became
apparent to organise
organisms
 The binomial classification
scheme was developed by
Carl Linneus in 1735
 To “put order into God’s
creation”
Jardins des Plantes Paris
© 2008 Paul Billiet ODWS

10. Comparative Anatomy
 Classification led to comparisons of
shape and form that gave rise to
comparative anatomy
 Comparative anatomists noticed that
different species have similar
structures used for different functions
(e.g. the pentadactyle limb of
terrestrial vertebrates).
 These are called homologous
structures
© 2008 Paul Billiet ODWS

11. The pendadactyle limb
Lizard © Chereka Keaton
Human
Frog
Bat
© 2008 Paul Billiet ODWS

12. Common ancestors &
missing links
 Evolutionists argued that if species
had been created independently by
a creator then there was a great
deal of coincidence in their design
 If all organisms evolved from a
common ancestor, this could
explain their common features
 Occasionally a fossil is found close
to the origin of a common ancestor
 These are called missing links
(e.g. Archaeopteryx a fossil
dinosaur with bird-like features)
Archaeopteryx
© 2008 Paul Billiet ODWS

13. Phylogenetics
 Classification led to phylogeny: the
study of related groups as revealed by
systematic classification
 Closely related organisms are more
similar than distantly related
organisms
 Currently the systematic analysis of
relatedness uses a technique called
cladistics
© 2008 Paul Billiet ODWS

14. Cladogram for the birds
Modern birds
no teeth,
horny beak
Archeopteryx
reversed first toe, fewer
than 26 tail vertebrae
Velociraptor
halfmoon-shaped
wrist bone
Allosaurus
three fingered hand
Coelophysis
three functional toes
and hollow bones
Titanosurus
Other
dinosaurs
Node
© 2008 Paul Billiet ODWS

15. Comparative Embryology
Early embryos of animals show surprisingly
similar features
revealing a common ancestry
© 2008 Paul Billiet ODWS

16. Comparative biochemistry
 Protein molecules the bottom line in studying the
phenotypes of organisms
 Similarities and differences in the amino acid
sequences of the same molecule
(e.g. haemoglobin) taken from different species
produce a phylogeny
 The phylogeny revealed by studying protein
structure reflects the same phylogeny as
comparative anatomy and embryology but with a
much finer resolution
© 2008 Paul Billiet ODWS

17. Molecular genetics
 Comparison of the base sequences of variable
regions of DNA (in particular mitochondrial DNA)
taken from different organisms
 The genotype is being analysed
 Rates of mutations are assumed to be constant
 The analysis of DNA provides a molecular clock
against which the geological clock can be
compared
© 2008 Paul Billiet ODWS

18. Biogeography
 Organisms are not found in every habitat that
they could occupy
 Travelling around the world the distribution of
organisms follows a simple pattern
 Two similar habitats that are close will contain
species that are closely related
 Two similar habitats separated by a great
distance (e.g. an ocean) will contain unrelated
species
 This distribution suggests that all organisms were
not created at the same time or they would be
evenly distributed all over the world
© 2008 Paul Billiet ODWS

19. Disjunct distributions
 Living or extinct organisms found in widely
different parts of the world were difficult to
explain
 The problem was resolved with the
development of the theory of plate
tectonics in geology
© 2008 Paul Billiet ODWS

20. Marsupial fauna
 Australia was once attached to India, Africa,
Antarctica and South America (Gondwana)
 This large continent broke up before the
placentals evolved
 The marsupials of Antarctica died out as it froze
over
 Those of Africa suffered from competition when
the placentals evolved
 Those of South America survived until the
Panama Isthmus was formed
 Only the Possum survived the competition form
North American placentals
© 2008 Paul Billiet ODWS