History of Evolution

History of Evolutionary Theory Anaximander to Austrian Monks

The Evolutionary Model
Evolution is based on two models of population change
Mutation—Change In DNA Structure—involves the creation of new life forms
Natural selection involves environmental pressures that favor, restrict, or eliminate life forms
Other factors may favor population change: gene flow (migration) or genetic drift (changes as the product of chance

Overview of Evolutionary Change
First, we look at the history of evolutionary thought from the Greek philosophers to the Darwinist model
Then we look at the mechanisms of evolutionary change
Biological, Molecular, and Population Genetics
Natural Selection
Other Mechanisms of Population Change
Speciation and Taxonomy

Overview of Evolution of Evolutionary Thought
History of Evolutionary Concepts
Greek Precursors
17 th Century Theologians
18 th Century Catastrophists
18 th Century Uniformitarians
Uniformitarianism of Hutton and Lyell
Darwin and Wallace
Gregor Mandel
Key concepts in evolutionary history
Essentialism/Chain of Being
Natural Selection/Mutation

Early Theorists: The Classical Greeks
Anaximander: (6 th Century BC)
Argued that men arose from fishes, setting the stage of
He relied on reasoning, not supernatural explanations
Plato and Aristotle: Set the stage for two models of existence
Essentialism, or the ideal type of biological lifeforms
Great Chain of Being, which placed all lifeforms in a hierarchical system of existence from lowest to highest.

Early Models: Essentialism
Essentialism: The ideal reality against which the perceived reality is compared and contrasted
Plato (above) was the first to come up with the ideal entity (including the human), against which the perceived entity was compared
Aristotle (below) also accepted the idea of a perfect universe, but did not accept the dichotomy that Plato posited. Rather, he saw the essential as the properties of each lifeform and other entities.
Greek gods and goddesses represented the ideal human male and female forms, as reflected in sculpture and other representational art.
Any deviation from the essential reflected some defect in any lifeform, animal or plant.

Early Models: The Great Chain of Being
A hierarchy of entities from the simplest to most complex anticipated the later rise of taxonomy; Karl von Linn é (discussed below) drew on this model.
In this view, the human race was the most complex and perfect of all living forms
Humans, however, were below the divine beings (including demons in the model depicted here.

Catastrophism
Earth’s history is product of sudden change
Example: Creation of Earth in six days (upper left), including Adam
Example: Flood (Noah’s Ark), which eliminated all life except Noah’s family and the male and female animals he allowed into the ark
Catastrophism does have some basis of reality: an asteroid that struck the earth 65 million years ago (lower left) nearly destroyed all life

Early Theorists: 17 th Century Catastrophists
James Ussher (1581-1656): Argued that humankind created noon, Oct. 23, 4004;(Upper left)
He based his calculations on biblical history and astronomy
Nicholas Steno (1638-1686):
Stratigraphy—sediments deposited by water in a sequence
Robert Hooke (1635-1703)
Described fossils (mineralized remains of lifeforms)
Recognized them as of extinct or early formative creatures
He also described the cell as the basic unit of life and invented the microscope
Adaptation : creatures changed as earth changed
All three explained history of earth as a catastrophic creation.

Early Theorists: 18 th Century Catastrophists
Carolus Linnaeus (Carl Linn é; 1707-1778)
Inventor of taxonomy —classification of lifeforms based on similarities and differences (Sample taxonomy next slide)
Viewed system as divinely ordained
He also classified human races as being of separate species with their own personality traits
Georges Cuvier (1769-1832)
Developed the science of comparative anatomy
Compared the Anatomy of present lifeforms with those of the fossils forms
Catastrophism: He concluded that the lifeforms of the world changed but they did not evolve

Carolus Linnaeus (Linn é)

Early Theorists: 18 th Century Uniformitarians
Uniformitarianism : Processes occur at same rate through time—present and past
Georges-Louis Leclerc (Comte de Buffon; 1707-1788)
He observed that the tides and currents of seas are uniform through time
He concluded that the earth had to be older than 6000 years
James Hutton (1726-1797): Discovered uniformity in 3 processes:
Deposit of strata under oceans
Uplifting seabeds to above sea level by volcanic action
Land erosion by water, wind, and decay
He too concluded that the earth had to be older than 6000 years

Uniformitarianism According to Charles Lyell
Charles Lyell (1797-1875)
Espoused extreme form of uniformitarianism by denying catastrophism ( Principles of Geology )
Three aspects hold up today
Geological processes of past are the same as today
Stratigraphy serves to reconstruct history of the earth
Immense amount of time necessary for geological processes to effect change in the landscape
Age of earth: The current estimate is 4.5 billion years

Counterevidence to Lyell’s Model
Five global catastrophes are known to have occurred.
Example: collision of asteroid with earth 65 m.y.a. wiped out 75% of world’s marine species)
Mississippi Delta is less than 100,000 years old—and has been shrinking since 3400 BCE

Evolutionary Theories: Acquired Characteristics
Jean-Baptiste de Lamarck (1744-1829)
Traits acquired in organism’s lifetime
Acquired Characteristics :
Are passed down to offspring
Product of adaptation to changing environment
Progress from simple to complex organisms
Example: elongation of giraffes’ necks to get at leaves of taller trees
Shortcoming:
No example to support theory; natural selection coupled with mutation better explain the lengthening of giraffes’ necks
Counterexamples abound; for example, generations of docking sheep's’ tails in rural Spain did not eliminate them.

Evolutionary Theories: Natural Selection
Natural selection Defined:
Evolutionary change by
Differential reproductive success of individuals
within a species (group of organism able to reproduce fertile offspring)
Through successful adaptation to an environment

Charles Darwin (1809-1882) Origin of Species
Charles Darwin (above) observed that pigeons, dogs, and horses were subjected to artificial selection in order to improve their breeding
On Galapagos Islands in 1832, Darwin observed that 14 species of finches adapted in different niches descented from a common ancestor (next slide)
He conceived the idea of natural selection and after years of dithering finally published his conclusions in The Origin of Species in 1859
Alfred Russel Wallace (below) drew the same conclusions—but Darwin published the results first
(Wallace made a bad career move: he sent his results to Darwin asking for comments. Oops!)

Charles Darwin and Natural Selection

Natural Selection: Definition and Implications
Variations are already present when selection occurs
Natural selection has no particular direction—change is random
Therefore, not all evolution is from the simple to the complex
Species can and do become extinct
New species can and do arise (Darwin had no way of explaining how the originated, however.)
Reproductive isolation makes for new species
New species fill new niches, as the finches showed
Thus, dark-winged moths filled a new environment in a soot-darkened coal-fired steel city; birds did not pick them off
The dark colored pepper moth is to the lower part of the photo

Evolutionary Theories: Genetics
It was up to the Austrian monk Gregor Mendel to discover the principle that would lead to the explanation how species originated.
He experimented with peas in monastery garden
In so doing, he found that smooth and wrinkled peas when combined produced offspring resembling their parents
Nothing but smooth peas appeared in generation 2
A ratio of 3 smooth peas to one wrinkled pea appeared in generation 3
The experiments provided the hereditary foundation for “origin” of species: mutation or genetic change

Gregor Mendel and Genetics
Mendel experimented with six other traits: color of peas, texture of pea pods, color of flowers
He found the same outcomes over three generations
The traits were each determined by variants (alleles) of a pair of genes.
Mendelian traits were thereby discovered
Later, it would be discovered that multiple genes could determine a single trait, such as eye and skin color

Molecular Genetics
The final step to understanding origins of species came with the discovery by James Watson (left) and Francis Crick (right) of a double helix molecule that determine traits of all species
Called DNA, they found that mutations could change the traits of a species—any species of a plant or animal.
Details of this process are discussed in the next set of slides.

Conclusion
Trends in history of evolutionary thought have been reviewed
Creationism to evolutionary models of change
Catastrophism to uniformitarianism
Essentialism to natural selection
Chain of being to variation by random mutation
Evidence fits evolutionary change better than model of creation
How evolutionary change occurs is covered in the next sets of slides.

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History of Evolution

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