Download history of Evolutionary Thought

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…
Jean-Baptiste de Monet de Lamarck
• 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!
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
Emu
(Australia)
Rhea
(S. America)
Ostrich
(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