EVOLUTION AND FIXITY © 2008 Paul Billiet ODWSODWS.

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


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


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


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


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


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


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


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


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


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


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


Comparative Embryology

Early embryos of animals show surprisingly similar features

revealing a common ancestry


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


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


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


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


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


EVOLUTION AND FIXITY © 2008 Paul Billiet ODWSODWS.

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