1. Descent with Modification & Darwin
Chapter 22

2. Early Contributions to Evolutionary Thought
Contributors to the development of Darwin’s ideas were:
Jean Baptiste de Lamarck ( )
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.

3. Early Contributions to Evolutionary Thought
Thomas Malthus ( )
Believed that populations increased in size until checked by the environment, called the ‘struggle for existence’.
Charles Lyell ( )
Developed the geological theory of uniformitarianism: the physical features of the earth were the result of slow geological processes that still occur today.
Charles Lyell
Herbert Spenser

4. Herbert Spenser ( )
Introduced the concept of ‘Survival of the Fittest’.

5. The Modern Theory of Evolution
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).
Darwin +
Mendel +
Weismann

6. The Development of Darwin’s Ideas
The first convincing case for evolution, The Origin of Species, was published by Charles Darwin in 1859.
In this book, Darwin argued that new species developed 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’.

7. Alfred Russel Wallace, a young specimen collector working in the East Indies, developed a theory of natural selection independently of Darwin. However, Darwin supported the theory more extensively and receives most of the credit for it.

8. History of Evolutionary Thought
Erasmus Darwin
Charles Darwin's grandfather and probably an important influence in developing his thoughts on evolution.
John Baptiste de Lamarck
First to publish a reasoned theory of evolution. Proposed idea of use and disuse and inheritance of acquired characteristics.
Rev. Thomas Malthus
Wrote: ‘An Essay on the Principles of Population’, attempting to justify the squalid conditions of the poor.
Hebert Spencer
Proposed concept of the ‘survival of the fittest’
Alfred Russel Wallace
‘Theory of Natural Selection’
Charles Darwin
‘Theory of Evolution by Natural Selection’
Charles Lyell
Major influence on Darwin.
Lyell’s work ‘Principles of Geology’ proposed that the earth is very old.
Gregor Mendel
Developed the fundamentals of the genetic basis of inheritance.
August Weismann
Proposed chromosomes as the basis of heredity, demolishing the theory that acquired characteristics could be inherited.
Julian Huxley
Ernst Mayr
T. Dobzhansky
Collaborated to formulate the modern theory of evolution, incorporating developments in genetics, paleontology and other branches of biology.
R.A. Fisher
J.B.S. Haldane
Sewall Wright
Founding of population genetics and mathematical aspects of evolution and genetics.
The New Synthesis
Neo-Darwinism: The version of Darwin’s theory refined and developed in the light of modern biological knowledge (especially genetics) in the mid-20th century

10. Lamarck’s Theories, 1809 Use and disuse Inheritance of acquired traits
Body parts of organisms can develop with increased usage and weaken with disuse
Inheritance of acquired traits
Body features acquired during the lifetime of an organism are passed on to offspring
Natural transformation of species
Organisms produce offspring with changes, transforming each subsequent generation into a slightly different form toward some ultimate higher order of complexity

11. Darwin’s Theory, 1840s -1850s
Natural selection is the differences in survival and reproduction among individuals in a population as a result of their interaction with the environment
Some individuals possess alleles that generate traits that enable them to cope more successfully in their environment than other individuals
The more successful individuals produce more offspring
Superior traits are adaptations to the environment and increase an individual’s fitness
“Survival of the Fittest”

12. The Development ofDarwin’s Ideas
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.

13. Observations of the fauna of the Galapagos Islands confirming his already formulated ideas from earlier in the trip. He found that most of the Galapagos species are endemic, but resembled species on the South American mainland.
Fossil finds of extinct species.
Evidence from artificial selection.

14. Natural Selection Overproduction Variation Natural Selection
Individuals show variation: some variationsare more favorable than others
Overproduction
Populations produce too many young: many must die
Natural Selection
Natural selection favors the best suited at the time
Inheritance
Variations are inherited. The best suited variants leave more offspring.

15. Darwin’s Finches

16. Principles of Natural Selection
Populations possess an enormous reproductive potential.
Population sizes remain stable.
Resources are limited.
Individuals compete for survival.

17. There is variation among individuals in a population.
Much variation is heritable.
Only the most fit individuals survive.
Evolution occurs as advantageous traits accumulate.

18. Types of Selection Stabilizing Selection Directional Selection
Disruptive (or diversifying) Selection
Sexual Selection
Artificial Selection

19. Sources of Variation Mutation Sexual reproduction Diploidy Outbreeding
Crossing over
Independent assortment of homologues
Random joining of gametes
Diploidy
Outbreeding
Balanced polymorphism
Heterozygote advantage
Hybrid vigor
Frequency-dependent selection