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 Cuvier2. Jean Baptiste Lamarck3. Thomas Malthus4. Charles Lyell5. Alfred Russell Wallace6. Charles Darwin

George Cuvier

• found evidence that new species appeared while other one disappeared

• 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

•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

Jean Baptiste Lamarck

we know today that Lamarck’s mechanism of evolution is incorrect, 1) implied desire for change and 2) survival of individuals

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

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

• 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.

a geologist

gradualism – in geology, the theory that geographical change occurs slow but steady processes

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 several important observations while on the Galapagos Islands (see fig 19.8, p. 654), especially the finches

→ noticed some similarities and differences between species of animals and plants on different continents

→ made observations while on the HMS Beagle, 5 year voyage

Summarizing Darwin’s Evidence1. 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. 653)

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 Galapagos

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 the past.

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 characteristics)

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 reproduce offspring like

themselves