• Greek philosopher• Examined nature world for evidence

of divine order• Scala naturae (“Chain of Being”)

• Hierarchical arrangement of forms• Species arranged linearly along a scale:

• formed the basis for the western belief in a fixity of species, each of which has a typical form

GodMan

MammalsEgg-laying animals

InsectsPlants

Non-living matter

Aristotle384 – 322 BC

Carolus Linnaeus1707 – 1778 AD

“The father of modern taxonomy”• Classified organisms with a binomial

system• Proposed a nested system of relationships

(as opposed to the Scala naturae)

• Recognized distinction between interbreeding vs. non-interbreeding organisms (same vs. different species)

• Believed in balance of nature• Each species has its place in a divine plan• Species do not change or go extinct

• Eventually acknowledged formation of new species by hybridization

“Dégéneration”• Believed life & species arise via material

processes• Looked for evidence in the physical & biological world

• Believed Linnean hierarchy reflected common descent (dégéneration), with divergence over time.

• Physical environment (somehow) changes organic particles• New species form when animals migrate, and new

environment changes them

• Change only happened within families: each family conforms to an internal mold, but species can change some over time.

Comte de Buffon1707 – 1788 AD

Charles’ Grandfather• British philosopher, naturalist & physician• Wrote Zoonomia: Or The Laws of Organic Life• Believed organisms constantly attempted to improve

themselves by adapting to their environment• Transformism, or transmutation

• All of life consists of “one living filament” connecting all living forms to a common ancestor

Erasmus Darwin1731 – 1802 AD

Inheritance of acquired characters• French professional naturalist• Theory of transformism

• “Simple” organisms constantly arise by spontaneous generation

• Organisms then progress through a hierarchy of ever-more-advanced forms (Scala naturae in reverse?)

• Philosophie zoologique (1809):• First law: Use or disuse of a structure leads to its

development or diminishment• Second law: These acquired characters can be passed

on to offspring

Jean-Baptiste Lamarck1744 – 1829 AD

Principle of overproduction• English clergyman• Major influence on Darwin & Wallace• Essay on the Principle of Population (1797)

• Most organisms produce far more offspring than can possibly survive

• Even when resources are plentiful, populations tend to grow geometrically until they outstrip their food supply

• Poverty, disease, and famine are inevitable, leading to a “struggle for existence”

Thomas Malthus1766 – 1834 AD

Uniformitarianism• English geologist• Another major influence on Darwin &

Wallace• Believed earth is constantly changing

• Processes that molded earth’s surface can be understood by modern-day processes

• Uniformitarianism: earth is subject to gradual, continuous change

• But there is no development or progress: earth remains at a steady state – in particular, species composition doesn’t change

Charles Lyell1797 – 1875 AD

The Man• An English “gentleman of private means”

• Was able to focus on his life’s work: the development of the theory of evolution by natural selection

Charles Darwin1809 – 1882 AD

The Voyage of the Beagle (1831–1836)

Charles Darwin1809 – 1882 AD

• Read Lyell’s Principles of Geology while on board (and correctly applied the principle of uniformitarianism to the formation of coral reefs)

• Developed an appreciation of biogeographical patterns

Biogeography on the Beagle

Charles Darwin1809 – 1882 AD

• Noticed that two similar species often coexisted in a “boundary zone” – neither one better adapted than the other

• These species must compete with each other

For example: The rhea, a flightless bird in South America

Biogeography on the Beagle

Charles Darwin1809 – 1882 AD

• Why do different groups of organisms live in areas separated by barriers (like the ocean)?

Why are the rhea and the ostrich so different, even though they have similar lifestyles under similar circumstances?

Would a creator be limited by boundaries to migration?

Biogeography on the Beagle

Charles Darwin1809 – 1882 AD

• Why do different groups of organisms live in areas separated by barriers (like the ocean)?

On the Galapagos Islands, Darwin noted that even islands that were very close together had giant tortoises that were distinct from one another

Back in Britain:The theory of natural selection

• Darwin recognized several critical facts:• Variability exists within species• Variant traits may be inherited (Darwin didn’t know how)• Malthus’s Principle of Overproduction implies that many

individuals must die or fail to reproduce• Individuals slightly better suited to their environment

must be more likely to survive

• Therefore, some variants will be preserved over time more than others. The composition of populations must change over time.

Charles Darwin1809 – 1882 AD

The origin of species• As natural selection acts on geographically

isolated populations, they become increasingly different from each other

• This leads to the formation of first varieties within a species, then separate species, then genera, etc., in an ever-branching process.

Charles Darwin1809 – 1882 AD

Natural selection co-discovered• English professional naturalist• In 1858, sent a letter to Darwin

describing his independent discovery of natural selection

• Like Darwin, travelled around the world observing biodiversity and biogeography

• Like Darwin, he’d read Lyell and Malthus, and eventually realized that “[the] self-acting process [of natural selection] would necessarily improve the race, because in every generation the inferior would inevitably be killed off and the superior would remain – that is, the fittest would survive.”

Alfred R. Wallace1823 – 1913 AD Image credits

Aristotle: www.columbia.edu/cu/philosophy/ admissions/text/process.htmlLinnaeus: www.nhm.ac.uk/library/linn/Buffon: www.ucmp.berkeley.edu/history/buffon2.htmlErasmus Darwin: science.ntu.ac.uk/erasmus.htmlLamarck: www.biol.unipr.it/aai/galleria/lamarck.gifMalthus: homepages.caverock.net.nz/~kh/bobperson.htmlLyell: athene.as.arizona.edu/~lclose/teaching/nats102/lyell.gifCharles Darwin: www.nirgal.net/ori_life1.htmlBeagle map: www.aboutdarwin.comRhea: www.sc.edu/library/spcoll/nathist/darwin/rhea.jpgOstrich: www.uct.ac.za/depts/fitzpatrick/docs/research.htmlTortoise: www.sandiegozoo.orgWallace: www.d.umn.edu/cla/faculty/troufs/anth1602/pchistory.html