EVOLUTION AND FIXITY © 2008 Paul Billiet ODWSODWS

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 ODWSODWS

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 ODWSODWS

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 © 2008 Paul Billiet ODWSODWS

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 ODWSODWS

Time to evolve The development of ideas in geology Starting in the 17 th 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 ODWSODWS

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 ODWSODWS

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 ODWSODWS

Systematics Collections of animals and plants in museums increased from 17 th 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 ODWSODWS

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 ODWSODWS

The pendadactyle limb Lizard © Chereka Keaton Human Frog Bat © 2008 Paul Billiet ODWSODWS

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 ODWSODWS

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 ODWSODWS

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 ODWSODWS

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

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 ODWSODWS

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 ODWSODWS

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 ODWSODWS

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 ODWSODWS

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 ODWSODWS