Untitled Document

Introduction to lectures on evolution

Learning objectives (from Course Information Document)

Summarise the evidence that led Darwin and Wallace to propose the theory of evolution by natural selection
Evaluate different available explanations for the origin of species
State the basis of genetic variation in populations
Define the terms natural selection, adaptation, fitness and sexual selection
Distinguish between morphospecies and biological species
Describe how speciation is thought to occur
Discuss the controversy over gradual versus punctuated modes of evolution

Definitions

Evolution	A description of and an explanation of the history of species - their origins, how they change, survive, become extinct. So evolution concerns both a historical account of life on earth AND an attempt to explain how observed changes have happened.
Ecology	The study of how living organisms interact with one another and with the physical environment.

Darwin and Wallace proposed two theories:

1. The living organisms we see today are all related by descent (common ancestry)

2. The means by which evolution occurs is a process of 'natural selection.'

organisms differ from one another i.e., there is variation
these differences are heritable, i.e. passed from generation to generation
many more organisms are born than survive and reproduce (mortality)
therefore, any variation that makes one offspring more successful than another will have a greater chance of being passed to the next generation ("survival of the fittest")

A Changing World View

Over the last 250 years our view of the living world has changed dramatically. This lecture reviews some of the key pieces of evidence that lead to this transformation.

From...

...to

Earth is young

In the 17th century Archbishop James Ussher used the Bible to date the origin of the earth as 4004 B.C. Vice-chancellor of Cambridge refined this to the morning of Sunday, October 23rd, 4004 B.C.

Fixity of species

Species are permanent, natural kinds. They do not change.
A fixed plan of creation.

Design

Living things seem designed for a purpose, and a design implies a designer.

Earth is ancient

Approximately 4,500,000,000 years old (radioactive isotopes)

Species evolve

Living things are constantly changing, new species arise and others go extinct
The history of life is contigent (e.g., mass extinctions)

Adaptation

Fit betwene organisms and their environment is due to natural selection ("blind watchmaker")
Organisms are often imperfectly constructed (nature as a "tinkerer").

This timetline shows some of the key people involved in this transformation (we will focus on the ideas, rather than the names and dates) (Campbell: see page 415, fig. 22.1)