Major Points
1. The"Great Chain of Being"
2. Evidence that species change over time
3. Darwin's theory of evolution
The Aristotelian World
Aristotle was a Greek philosopher of the 4th century B.C.
Was one of the earliest naturalists
Created a theory of the world as a whole
Believed nature was a continuum of organization from the lifeless to the
most complex forms
Divided the biological world into observable types
The "Great Chain of Being"
Aristotle believed that all living things could be rank ordered from the
least to the highest (humans)
The Great Chain of Being proposed that all "species" of animals
were linked in a logical progression
This metaphor extended into all other areas (cosmology, politics, society,
etc.)
A Static System
The Great Chain of Being assumed that species were unchangable ("immutable")
"Natural species" had always appeared as the do now
They had all be created at the same moment
Geological change was also "gradual", the same processes had always
been at work
A System of Classification
Based on the Great Chain of Being, naturalists sought to catalog living
things
Linnaeus was the most successful
He created a classification system which assumed the interrelation of species
This was not an evolutionary systemThe species were not related by descent,
but by design
Evidence Against the Static View
The apparent age of the Earth
Geographical distribution of animals
Anatomical similarities among species
Existence of an apparent progression of species in the geologic record
Gradually scientists proposed non\endash static models in which species
change over time
Catastrophism
Attempted to negate the available evidence
It stated that species were immutable
Catastrophes occured which wiped out most life on Earth
Existing species then would repopulate (these species were simply much less
numerous before the catastrophe)
The fossil record refutes this theory
Lamarkianism
An early attempt to explain how species might change
Individual organisms adapt to their environment
They pass on these changes to their offspring
There is no evidence for this view
Darwinism
Charles Darwin was a trained minister in the Church of England who was an
avid naturalist
He traveled for 5 years on H.M.S Beagle as a naturalist
His observations led him to propose a theory describing the mechanism of
evolution
Remember, he did not invent "evolution"
Darwin & Malthus
Thomas Malthus wrote that human populations grow exponentially (doubling
every so many years)
The food supply does not
Therefore, crises occur in which indivi-duals compete for limiting resources
Darwin applied this theory to natural history
Natural Selection
Given that populations excede resources:
Individuals will compete for limiting resources
Differences in "form and function" affect the ability to compete
"Adaptive" traits should increase in frequency over generations
So populations can evolve because of this "natural selection"
(changes are inherited)