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19.2 – Developing the Theory of Evolution
There were several ( we study six) scientists who
contributed or presented ideas about how
evolution occurs:
1. George Cuvier
2. Jean Baptiste Lamarck
3. Thomas Malthus
4. Charles Lyell
5. Alfred Russell Wallace
6. Charles Darwin
George Cuvier
•French scientist who developed the science
of paleontology (the study of fossils)
•noticed that organisms found in lower layers
of sedimentary rock were dissimilar to
organisms found today, and as you continue
up the layers the organisms begin to more
closely resemble modern day organisms
• found evidence that new species appeared while other one
• catastrophism – the idea that catastrophes such as floods,
diseases, or drought periodically destroy species in a
particular region, allowing species from neighboring
regions to repopulate that area
Jean Baptiste Lamarck
French naturalist who proposed on of the
earliest ideas about evolution in 1809
idea of use and disuse – idea that body
parts that were used extensively to cope with
conditions in the environment would become
larger and stronger
inheritance of acquired characteristics – theory that
characteristics acquired during an organism’s lifetime could be
passed on to its offspring
we know today that Lamarck’s mechanism
of evolution is incorrect, 1) implied desire for
change and 2) survival of individuals
Thomas Malthus
• an English economist who wrote “Essay
on the Principles of Population”
• Darwin read the essay and it helped to
refine his ideas about evolution; the key
point was that plant and animal
populations grow faster than their food
supply and eventually a population is
reduced by starvation, disease, or other
factors (war)
Charles Lyell
a geologist
gradualism – in geology, the theory that
geographical change occurs slow but
steady processes
• uniformitarianism – in geology, theory that
geological processes repeat themselves.
Change occurs through slow but steady
processes. The key to understanding geological
processes of the past lies in understanding
geological processes of the present.
Alfred Russell Wallace
• came to the same
conclusions as Darwin;
worked independently
• Little recognition!!
Sound familiar?
Charles Darwin
→ English naturalist who developed the
theory of natural selection using his own
observations, and work from Malthus,
Cuvier, and Lyell
→ made
observations while on the HMS Beagle, 5 year voyage
→ noticed some similarities and differences between species of
animals and plants on different continents
→ made several important observations while on the Galapagos
Islands (see fig 19.8, p. 654), especially the finches
Summarizing Darwin’s Evidence
1. Plants and animals observed in the temperate regions of South
America were more similar to plants and animals in the South
American tropics than to plant and animals in other temperate
regions of the world.
2. Darwin found fossils of extinct animals that looked very similar
to animals presently living in the same region (see fig 19.6, p.
3. Plants and animals living in the Galapagos Islands closely
resembled plants and animals living on the nearest continental
coast (the west coast of South America)
4. Species of animals (such as tortoises) that at first looked
identical actually varied slightly from island to island in the
5. Finches collected in the Galapagos Islands looked similar to
finches from South America but were, in fact, different species.
Finch species also varied from island to island
6. After reading Lyell’s work, Darwin understood that geological
processes that are slow and subtle can result in substantial
changes. As well, forces that affect change are the same as in
Darwin’s Theory of Natural Selection
• Descent with modification – Charles Darwin’s theory that
natural selection does not demonstrate progress (or evolution)
but merely results from a species ability to survive local
conditions at a specific time
Summary of Darwin’s ideas
• Natural selection means that organisms with traits best suited
to their environment are more likely to survive and reproduce.
The factors Darwin identified that govern natural selection are:
(1) organisms produce more offspring than can survive, and
therefore organisms compete for limited resources
(2) individuals of a population vary extensively, and much of this
variation is inheritable
(3) those individuals that are better suited to local conditions
survive and produce offspring
(4) processes for change are slow and gradual
Comparing Lamarck’s and Darwin’s Theories
Question: Why is it that giraffes have long necks?
Lamarck’s answer:
→ giraffes stretched their necks in order to reach the
leaves in trees to eat (law of use and disuse)
→ the stretched neck acquired throughout a parent’s life
was passed on to its offspring (inheritance of acquired
Darwin’s answer:
→ in the beginning, there were giraffes with short necks
and giraffes with long necks
→ the long-necked giraffes could reach the food easier
while short-necked giraffes could not. The short-necked
giraffes died off due to starvation
→ the long-necked giraffes produced more giraffes with
long necks, and eventually all giraffes has long necks
Comparing Lamarck’s and Darwin’s Theories
Lamarck’s :
→ Survival of individuals
→ Acquired characteristics inherited
Darwin’s :
→ Survival of populations (individuals die)
→ Variation already exists in populations
→ Best adapted survive and reporduce offspring like