Charles Darwin (1809-1882)

1
Charles Darwin (1809-1882)

• Origin of Species
• among the most influential texts of this century

2
Charles Darwin (1809-1882)

• Studied Medicine at Edinburgh
• Switched to become a clergyman
• at Christs College, Cambridge University
• Passionate interest in Natural History
• Reverend (Professor) John Henslow encouraged him
  to pursue Biology
• In 1831 invited as a naturalist on the HMS
  Beagle, a ship sent by British Navy to chart the
  waters of South America

3
HMS Beagle off of South America

• When Darwin left on the Beagle Evolution was
  already a popular idea for explaining the fossil
  record.
• However, there were no known mechanisms
• Darwin did not believe in Evolution, but Rev.
  Henslow gave him a book to take with him
  Lyells Principles of Geology

4
Historical Context

• By mid-1800s scientific context was in place for
  development of theory of Evolution.
• Developments in Geology
• Earth more than 6,000 years old
• Fossil Record showed change in species over
  time
• The mechanisms for Evolution were missing, and
  were hotly debated

5
Influences on Darwin

• Geology Darwin had Lyells Principles of
  Geology on board the HMS Beagle
• Lamarck s (1744-1829) Theory of Evolution
• Inheritance of acquired characteristics
• Malthus (1766-1834) Competition within species
  and struggle for survival

6
Influences on Darwin
Lyells Principles of Geology

• Darwin had Lyells book on board the HMS Beagle,
  given to him by his botany professor, Reverend
  John Henslow
• Fossil record
• the earth is old
• many animals that once existed are now extinct
• there are layers (strata) in the fossil record
  show a pattern of change

7
Influences on Darwin
Jean-Baptiste Lamarck (1744-1829)

• Proposed most influential
• mechanism of evolution before Darwin
• Inheritance of acquired characteristics
• Introduced the idea of adaptation, but got the
  mechanism wrong

http//www.ucmp.berkeley.edu/history/lamarck.html
8
Influences on Darwin

• Malthus (1766-1834)
• Essay on the Principles of Population

• Competition not all individuals could survive
• Rate of population growth gtgt Rate of increase in
  food supply
• Darwin concluded that individuals that are better
  adapted would be the ones that survive and leave
  more offspring

9

• Darwin held on to his work on natural selection
  for 20 yrs without publishing
• Alfred Wallace (1823-1913) came up with the idea
  of natural selection independently
• Darwin rushed to publish Origins in 1859 when he
  learned of Wallaces work

10
Alfred Russel Wallace (1823-1913)

• On the Tendency of Varieties to Depart
  Indefinitely from the Original Type
• Based on his work in the Malay Archipelago

11
Darwins Main Points

• (1) Organisms Evolve (Darwin not first)
• (2) Common Descent species arise from common
  ancestors
• (3) Gradualism changes are gradual (still
  debated)
• (4) Population Speciation change in proportions
  of individuals having a trait in a population
• (Darwins original idea)
• (5) Natural Selection mechanism (Wallace also)

12
Lamarck vs Darwin

• Lamarck inheritance of acquired traits (not
  mutations)--Individual evolution
• Evolution at the Population Level

13
Lamarck

• Individuals are evolving
• If you got a tan, youd pass it on

14
Lamarck

• Individuals are evolving
• If you got a tan, youd pass it on

Balls get tan
15
Lamarck

• Individuals are evolving
• If you got a tan, youd pass it on

Tan balls have offspring that are also tan
16
Lamarck

• Individuals are evolving
• If you got a tan, youd pass it on

Some get more tan
17
Lamarck

• Individuals are evolving
• If you got a tan, youd pass it on

And then pass on their acquired traits
18
Darwin

• Natural Selection

19
Darwin

• Natural Selection

A heritable change (now known as a mutation)
20
Darwin

• Natural Selection

Selection favors
21
Darwin

• Natural Selection

Greater Fitness
22
Darwin

• Natural Selection

Greater Fitness
The individuals themselves are not changing, but
the population is the unit of evolution
23
Darwins unique contribution

• Population Speciation as a result of Natural
  Selection
• More offspring are produced than can survive
• Limited resources and competition for resources
• There is variation in a population
• Individuals better adapted to environment survive
• Survivors leave more offspring (Survival of the
  Fittest)
• Thus, average character of population is altered

24
Darwins Mockingbirds (studied Tortoises and
finches later)
Galapagos Islands
"My attention was first thoroughly aroused by
comparing together the various specimens ... of
the mocking-thrush" C. Darwin, The Voyage of
the Beagle (1839)
25
Darwins Mockingbirds
Galapagos Islands

• Only one species of mockingbird in South America
• But, on each island there was a different
  species
• Mockingbirds on different islands shared traits
  that suggested a shared common ancestor--and were
  not independently created

26

• So Darwin did NOT originate
• the idea of Evolution
• BUT he provided a plausible Mechanism
• and much evidence

27
But, Darwins theory was not complete

• Because Darwin knew nothing about mutation, he
  had no idea how variability was generated in
  populations (Lecture 5)
• Because Darwin knew nothing about genetics or
  genes, he had no idea how variability was passed
  on to offspring (Mendel)
• Darwin did not know about nonadaptive
  evolutionary forces, such as Genetic Drift
  (Lecture 3)

28
Mendels work held part of the key to what was
missing in Darwins Theory

• Mendel published in 1865 was ignored until 1900
• Presented a mechanism for how traits got passed
  on
• Individuals pass alleles on to their offspring
  intact
• (the idea of particulate (genes) inheritance)