EVOLUTION

Transformation of the Biological Paradigm

Evolution

• Charles Darwin

• BUT, the history of Evolutionary Thought pre-dates Darwin considerably…

The Aristotlean-Christian World View

• Aristotle (350 BC)– Greek

• Special Creation & Fixety of Species– Every creature has its place, and all have

been created in a specific and perfect form by an omnipotent & omnipresent creator.

– No change – each organism is created in its most ideal form.

The Aristotlean-Christian World View

• Aristotle observes life’s complexity &

Suggests a “Hierarchy of Life”:

Complexity

The “scala naturae”

The Aristotlean-Christian World View

• Following Aristotle (and all the way up into the 1700’s), this is the unchallenged world view.

• Taxonomy (Identification & Naming of organisms) centers around placing newly discovered species properly into the pyramid (Linnaeus).

Naturalists begin to find problems

• Some organisms were not fitting properly into the hierarchy.

• Due to Variations– Viewed as imperfections of an idealized form.– Which characteristics of an organism are most

important for placing it in the hierarchy?– How much variation should be viewed as

normal within a species?

Georges Louis LeClerc DeBuffon

• (1707-1788)• Wrote a huge “Natural History”• Observed much Variation.• Suggested the possibility of “Descent with

Modification”– As organisms descend through time, modifications of

the basic form occur due to differences in environment, geographic isolation, overcrowding, etc.

– Offered no mechanism for such modification.– Suggested the Earth was only 168,000 years old.

Erasmus Darwin

• (1731-1802)• Charles Darwin’s Grandfather• Physician

– Examined the Anatomy of many organisms.– Found Vestigial Organs (non-functional).

• Why would these be present in a perfectly-adapted organism?

– Examined changes during development (Ontogeny).

• Suggested some sort of “Common Descent”– Currently living organisms have descended from

ancestors of similar (but slightly different) form.– Offered no mechanism for such modification.

James Hutton

• (1726-1797)

• Geologist

• Suggested “Gradualism”– Changes to the Earth occur gradually through

continuous processes…the same processes that are occurring right now:

• Erosion• Volcanic activity• Earthquakes

Charles Lyell• (1797-1875)• Geologist

(father of “modern Geology”)• Suggested “Uniformitarianism”

– Following Hutton’s ideas, Lyell suggested that the rate at which geologic events occur is both slow and uniform (gradual).

– The same processes are responsible for both past and present geologic events…the geologic processes occurring now have been occurring over many millions of years.

– Leads to the conclusion that the Earth is very old – “many millions of years old”.

Georges Cuvier• (1769-1832)• Zoologist.• Comparative Anatomy of bones & muscles.

– Similarities in structure, despite function.

• Fossils (impressions of dead organisms in rock).– Slight differences in fossil forms found in

different rock strata (layers of different age).

– Was firmly entrenched in the Aristotlean-Christian View, so introduced Catastrophism as an explanation.

• Sporatic catastrophies in the Earth’s history killed off certain species – those not found currently.

Jean-Baptiste de Monet de Lamarck

• (1744-1829)• Naturalist• Examined Rock Stratigraphy.

– Fossils from the oldest strata appeared simpler, while those from more recent strata appeared more complex.

• 1st to fully support “Common Descent” and suggest a link between biological diversity and adaptation to the environment.

• Proposed a mechanism…

• Suggested that CHANGE in organisms took place by “Inheritance of Acquired Characteristics”.– Characteristics acquired during an organism’s

life were passed on to offspring.– Giraffe Necks became longer and longer as

each generation stretched higher into the trees for food.

• Problem…

Jean-Baptiste de Monet de Lamarck

• Lamarck’s hypothesis was never supported by experiments.

• Why? …

• An environmentally-induced phenotype cannot be passed on to the next generation…only genotype can!

• Lamark’s mechanism has long since been DISPROVED, but he is still remembered for this mistaken hypothesis!

Jean-Baptiste de Monet de Lamarck

Charles Darwin

• (1809-1882)• British Naturalist • Supporter of the Aristotlean-Christian Worldview.• Began science in Medical School at Edinburgh• Became more interested in nature (birds

particularly), and quit Medical School.• Enrolled at Christ’s College at Cambridge to

become a priest…still more interested in nature (especially collecting beetles).

Charles Darwin

• Finished School and planned to start a church in the countryside.

• Before graduation, though, he gained an avid interest in Geology.

• Was invited by former professors to become a Naturalist aboard the HMS Beagle – a ship destined for a sailing trip around the world.

Charles Darwin• 5 year voyage (1831-1836)• Lots of DATA!

1. Geologic• He saw first hand what Hutton had suggested

(Gradualism), and agreed with Lyell’s premise that the Earth must be very old.

• He examined many fossils – some resembling modern (current) organisms, but not exactly.

– Saw the possibility for Descent with Modification (modern forms having descended from now-extinct forms), and for organisms changing over time.

Charles Darwin…DATA

2. Biogeography• He found similar organisms in far-reaching places,

but in similar habitats.– Suggested that organisms may be adapting

to the same types of environment, despite the distance between them.

• He found slight variations in organisms found in slightly different habitats (but separated from each other … Finch Bills, Tortoise Necks, etc.)

– Suggested that a common ancestor gave rise to the different varieties, which each adapted to slightly different environments.

Darwin’s Biogeography

EmuEmu

RheaRhea

OstrichOstrich

(Australia)(S. America)

(Africa)

Darwin’s Biogeography

Charles Darwin

• Returned from the voyage and…PUBLISHED!

• Saw that adaptation to environment was indeed real, and eventually formulated a mechanism for it, but…– He did not want to jeopardize his scientific

status, so didn’t publish it.

• Along came Alfred Russel Wallace…

Alfred Russel Wallace• (1823-1913)

• Naturalist

• Studied and admired Darwin’s work.

• Wrote Darwin to see what he thought about a hypothesis regarding a mechanism for adaptation to the environment.

• This hypothesis was virtually the same as Darwin’s (unpublished) ideas about how change could take place!

Darwin & Wallace• 1858 -- Presented their hypotheses at a meeting

of the Linnaean Society (London):

"The Variation of Organic Beings under Domestication and in their Natural State"

"On the Variation of Organic Beings in the State of Nature; on the Natural Means of

Selection; on the Comparison of Domestic Races and true Species"

Darwin

• Later (1859) published his famous essay:

“I have called this principle, by which each slight

variation, if useful, is

preserved, by the term Natural Selection.”

- Charles Darwin, The Origin of

Species