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Evolution
Darwin
Major Contributions to Evolutionary
Thought
Contributors to the development of Darwin's ideas were:
Jean Baptiste de Lamark (1744-1829)
 Believed that organisms could pass on traits acquired during their lifetime
 - Discredited: when the mechanisms of heredity became known
 - Important: because he was the first to propose that change over time was the result of natural
phenomena and not divine intervention
Thomas Malthus (1766-1834)
 Believed that populations increased in size until checked by the environment, called the 'struggle
for existence'
Charles Lyell (1797-1875)
 Developed the geological theory of uniformitarianism - the physical features of the earth were
the result of slow geological processes that still occur today
Hebert Spenser (1820-1903)
 Introduced the concept of 'Survival of the Fittest'
The modern theory of evolution combines the following ideas:
 - Darwin's theory of the origin of species by natural selection - - with an understanding of
genetics (from Mendel)
 - and the chromosomal basis of heredity (from Weismann)
This synthesis is called NEO-DARWINISM
The Development of Darwin's Ideas
The first convincing case for evolution, The Origin of Species, was published by Charles
Darwin in 1859
In The Origin of Species, Darwin argued that new species changed from ancestral ones
by natural selection
Darwin developed his theory of "survival of the fittest" by building on earlier ideas and
supporting his views with a large body of evidence he collected while voyaging
extensively on the ship the 'HMS Beagle'
Alfred Russel Wallace, a young specimen collector working in the East Indies,
developed a theory of natural selection independently of Darwin -·but Darwin
supported the theory more extensively and receives most of the credit for it
Darwin's theory was supported by data collected from:
 The flora and fauna of South America - these showed different adaptations for
diverse environments but were distinct from the European forms
 Observations of the fauna of the Galapagos Islands confirmed his already formulated
ideas from earlier in the trip - finding that most of the species live nowhere else in the
world, but resembled species on the South American mainland
 Fossil finds of extinct species
 Evidence from artificial breeding
The Concepts of Darwinism
Darwin's view of life was of 'Descent with Modification' descendants of ancestral forms
adapted to different environments over a long period of time
The mechanism for adaptation is called 'Natural Selection', and is based on a number of
principles:
 Overproduction
Species produce more young than will survive to reproductive age (they die before
they have offspring)
 Variation
Individuals vary from one another in many characteristics (even siblings differ) - with
some variations being better suited to the conditions of the time than others
 Competition
There is competition among the offspring for the resources needed for life - food,
habitat etc.
 Survival of the Fittest Phenotype
The individuals with the most favourable combinations of characteristics will be
most likely to survive and pass their genes onto the next generation
 Favourable Combinations Increase
Each new generation will contain more offspring from individuals with favourable
characters than those with unfavourable ones