Development of Evolutionary Theory

and… Darwin’s voyages

and… Natural Selection

Aristotle

• 384-322 B.C. – Aristotle – wrote the Scala Naturae, or ladder of life.

• It described a Great Chain of Being which had a graduating complexity.

• Humans were on top. • There was not mention of

transformation, extinctions. Organisms were immutable.

Archbishop James Usher

• 1650 – Archbishop James Usher of Armagh declared that the Earth was created on Sunday October 23 4004 B.C.

Carolus Linnaeus

• 1700’s - Linnaeus wrote the Systema Naturae, thus developing taxonomy.

• The classification system of

Genus species

was introduced.

Thomas Malthus

• 1766-1834 – Thomas Malthus – An essay on the Principles of Populations

• stated that reproductive increases are geometric.

• Excess fertility creates more offspring than the environment can sustain.

Jean Baptiste Lamarck

• 1809 – Lamarck developed the theory of transformism – the transmission of acquired characteristics. E.g. Giraffe.

• Environment plays a role

Baron Georges Cuvier

• 1769-1832 – Baron Georges Cuvier developed the theory of Catastrophism, which explained that catastrophes in the past caused the extinction of local species

• Cuvier is the founder of palaeontology (Ross in Friends)

Sir Charles Lyell

• 1798-1875 – Sir Charles Lyell, a geologist

• Uniformitarianism • The geological

processes we see today are the same that they have always been.

• Wrote a book on geology

Sir Charles Darwin

• At 16 was sent to medical school… he thought it was boring, and left

• Enrolled at Christ College at Cambridge to become a clergyman (at this time, most prominent naturalists and scientists were clergymen)

• Graduated in 1831 at age 21

Sir Charles Darwin• Reverend John Henslow, a

professor of botany, introduced Darwin to Captain Robert FitzRoy (HMS Beagle), and gave Darwin Lyell’s book

• Set out on the HMS Beagle for 6 years as the captains companion (unofficial naturalist)

• Mission was to chart the South American coast

• While the ship was on the coast, Darwin would go ashore and collect specimens of local animals and plants, as well as fossils of extinct animals

I’m on a boat

Voyage of the Beagle

Darwin’s Finches• While on the

Galapagos islands, Darwin collected samples from 13 similar but separate species of finches

• Different beak shapes and sizes specialized for a particular food source

Darwin hypothesized that the finches must have all had a

common ancestor. He also found fossils of hippo

sized rodents. The similarities of the fossils to modern day rodents

led him to believe species changed over time.

Sir Charles Darwin• The fossils led Darwin to believe

that existing animals were descended from extinct animals,

• He wrote an essay on Natural Selection in 1844

• Darwin was excessively meticulous, and didn’t publish his essay on Natural Selection

• He spent 8 years studying barnacles on the suggestion of a friend

• He did this because he wanted to thoroughly understand the natural selection of at least one species

On the Origin of Species

• 1856, Darwin had amassed so much more evidence for evolution, that he re-opened his 1844 essay.

• In 1858, Darwin received a letter from Alfred Russell Wallace. A naturalist working in Indonesia, that described the changing of species over time. 12 days after reading the letter, Darwin read Wallace’s letter and a portion of his 1844 essay to the Linnaean Society.

• On the Origin of Species by means of Natural Selection was published in November 1859. It was over 1000 pages long.

• It sold out Harry Potter, eat your heart out.

Some people didn’t like it

Natural Selection

Observation 1All organisms increase in a geometric ratio (excess

fertility)Observation 2

The number of any given species tends to remain constant, in spite of its potential

DeductionThere is a universal struggle for survival and success is measured in leaving viable offspring

Observation 3All living things vary; even parts may vary to some

degreeDeduction

Individuals possessing any advantage, no matter how small, have a better chance of surviving to leave viable offspring

Homologous, Analagous and Vestigial Structures

Homologous structures

• Features that have a common origin, but a different function

Analogous Features

• Features that have a similar function, but have a different origin

Vestigial Features

• Homologous characters of an organism which seem to have lost all of their original function

The human appendix

The wings of flightless birds (some penguins)

Cartilage in the human ear

Hip bones in whales