EVOLUTION AND FIXITY
© 2008 Paul Billiet ODWS
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
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
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 Ussher1580-1656
© 2008 Paul Billiet ODWS
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
Time to evolve
The development of ideas in geologyStarting 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
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 – 1832Public Domain Image
© 2008 Paul Billiet ODWS
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
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
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
The pendadactyle limb
Lizard © Chereka Keaton
Human
Frog
Bat© 2008 Paul Billiet ODWS
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
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
Cladogram for the birds
Modern birdsno teeth,
horny beak
Archeopteryx reversed first toe, fewer
than 26 tail vertebrae
Velociraptor halfmoon-shaped
wrist bone
Allosaurus three fingered hand
Coelophysisthree functional toes
and hollow bones
Titanosurus
Other dinosaurs
Node
© 2008 Paul Billiet ODWS
Comparative Embryology
Early embryos of animals show surprisingly similar features
revealing a common ancestry
© 2008 Paul Billiet ODWS
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
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
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
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
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
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