Transcript The History of Evolutionary Thought

The History of Evolutionary Thought
Today: begin consideration of evolution with historical overview.
Reasons:
1. See how Darwin and others arrived at their understanding of evolution
(which now forms the basis of our current understanding).
2. Understand the philosophical implications of Darwin's theory important to understand the significance of his ideas (also, helps explain
continuing opposition).
The History of Evolutionary Thought
Darwin was not the first to introduce the concept of “change” (it was not
called evolution, even in his time) in biological thinking.
Herakleitos (ca. 500 BCE) believed the universe was in constant state of flux.
Other Greek philosophers also believed change was the norm.
Plato (424 – 348 BCE) Later philosophers regarded the universe as more static.
Major concept: Every object formed around a perfect essence or type. Also
called idealism
a. Called ειδοσ. (eidos) Root of the word ideal.
b. The philosophy of essentialism (idealism) held that there are two
coexisting worlds: an ideal eternal real world and an illusionary imperfect
world that humans perceive with their senses.
The History of Evolutionary Thought
To Plato, variations in plant and animal populations were merely imperfect
representatives of ideal forms-"shadows on the wall" or "reflections in
water"- imperfect reflections of the perfect ideal; however these perfect
ideal forms only existed in a "real" world not visible to humans.
This type of thinking has serious ramifications for biology (and acceptance of
Darwin’s theory), why?
Typological thinking persists
Aristotle 384 BCE – 322 BCE
Aristotle’s Scala Naturae – The Great Chain of Being
Soame Jenyns (1757). “The
universe resembles a large and
well-regulated family, in which all
the officers and servants, and
even the domestic animals, are
subservient to each other in a
proper subordination; each
enjoys the privilege and
perquisites peculiar to his place,
and at the same time
contributes, by that just
subordination, to the
magnificence and happiness of
the whole.”
Explaining gaps in the Great Chain of Being
Voltaire (1694-1778) was perhaps one of the first to dispute the concept of
such a hierarchy, particularly in a social structure.
• But he also addressed the question of the many gaps among the species,
which did not seem to be in accord with the expected innumerable steps
in the continuous progression from imperfect to perfect.
• He proposed that such gaps were the result of extinctions.
• In this manner, he echoed the thoughts of other philosophers; Descartes
(1596-1650) and Leibniz (1646-1716).
Explaining gaps in the Great Chain of Being
Leibniz suggested that such gaps might not only be due to extinction, but to
the transformation of species. He even suggested that different species
that presently share common features might at one time have been a
single race.
a. To Leibniz, evolution of a species was tied in with the perfection toward
which the universe continually progressed, and his philosophy
represented a major shift from a perfectly created universe to one in
the process of becoming perfect. (note the chink in the armor of the
fixity of species).
Explaining gaps in the Great Chain of Being
Such progress toward perfection fitted nicely with the thinking of Bonnet
(1720-1793), who maintained that the development of any organism from
its “seed” was an unfolding of a preconceived plan inherent in the seeds
of previous generations. [Sounds like ontogeny recapitulates phylogeny.]
Explaining gaps in the Great Chain of Being
Thus, in spite of its idealistic nature,
the Great Chain of Being led almost
directly to the idea that the perfection
of organisms may demand multiple
intermediary stages.
By the eighteenth century the basic
concept of evolution, the actual
transformation of one species into
another, can be said to have been
merely awaiting the philosophical
acceptance of actual change between
the innumerable steps in the Great
Chain of Being.
Note: Similarity to “Progress of Man”
The fixity of species was incorporated into Judeo-Christian thought.
In the 1600’s, nature came to be studied Ad majorem Dei gloriam - "for the
greater glory of God" .
Groundwork for Darwin was laid by Karl von Linné (1707 – 1788).
Better known by his Latin binomial, Carolus Linnaeus
Found of modern systematics – wrote the seminal Systema Naturae,
which described and classified ALL known species of plants and animals
of his time (over 11,000).
Hierarchical classification scheme of Linnaeus.
The phrase, “no new
species can arise”
disappeared in later
editions of the System
Naturae.
Linnaeus toyed with
the idea of “species as
the children of time.”
Pre-Darwinian proponents of evolution
Erasmus Darwin, 1731 - 1802
…how life evolved from a single
common ancestor, forming “one
living filament”
Pre-Darwinian proponents of evolution
Buffon - 1707 - 1788
Mentioned concepts that Darwin used:
competition, variation, extinction.
Echoed the idea that species were not
immutable, but never pulled it all
together.
Georges-Louis Leclerc, Comte de Buffon
Pre-Darwinian proponents of evolution
Georges-Louis Leclerc, Comte de Buffon
Roadblocks to developing the concept
of evolution:
1. New species had not appeared
during recorded history.
2. Matings between different species
led to either inviability or sterility of
the hybrids (think horses). How
then could individuals of a single
species be separated from their
own kind to produce a new
species?
3. Where are all the missing links
between existing species if
transformation from one to the
other has taken place?
4. It was contrary to religion.
Pre-Darwinian proponents of evolution
Philosophie Zoologique (1809)
His thinking was driven in part by the
concept of teleology – the use of design
or purpose as an explanation of natural
phenomena.
Jean Baptiste Lamarck (1744-1829).
Pre-Darwinian proponents of evolution
Jean Baptiste Lamarck (1744-1829).
Lamarck could not
accept extinction, so
the Scala Naturae now
becomes an escalator!
Pre-Darwinian proponents of evolution
Proponent of two main principles
1. Use and disuse – features that are used are accentuated and
features that are not used deteriorate.
Jean Baptiste Lamarck (1744-1829).
2. The inheritance of acquired characteristics – the modifications
from use and disuse could be passed on to offspring.
Lamarck was incorrect, but his approach was progressive at the
time. Why?
Contributions from Geology.
Two schools of geological thought emerged during the 18th and 19th
centuries - catastrophism and uniformitarianism.
Catastrophism
Proponents included:
George Cuvier (great French paleontologist)
Louis Agassiz (Swiss-born naturalist)
Catastrophism was consistent with Christian dogma - Biblical creation.
Extinction was real (compare with Lamarck).
Cuvier disbelieved the Scala Naturae. All organisms were equally well-designed
in his eyes, and thus not hierarchically rankable.
Contributions from Geology.
Two schools of geological thought emerged during the 18th and 19th
centuries - catastrophism and uniformitarianism.
Gradualism (later Uniformitarianism, thanks Lyell)
Proposed by Scottish farmer and scientist James Hutton (1726-1797).
Earth was shaped by processes that can be observed today (e.g., erosion,
sedimentation, volcanism) acting over immeasurably long periods of
time.
"We find no vestige of a beginning, no prospect of an end.“
uniformitarianism- geological process must balance out:processes that
build mountains are eventually balanced out by erosion.
Contributions from Geology.
Two schools of geological thought emerged during the 18th and 19th
centuries - catastrophism and uniformitarianism.
Uniformitarianism
William (Strata) Smith (1815). The source of the yardstick of time.
A canal surveyor who walked all of England looking at rocks. He recognized
that certain fossils re-occurred in consistent groups, and essentially defined
units of rock.
This led rapidly to the conclusion that different periods of earth history were
characterized by different critters, and that rocks containing the same
critters, must be of the same age!
Contributions from Geology.
William (Strata) Smith (1815). The source of
the yardstick of time.
Smith provided a scale against which to
measure change through Hutton’s
immeasurable time – in other words – he
enabled the recognition of RATE. This made
Hutton’s uniformitarianism conceivable.
Contributions from Geology.
Principles of Geology (1830 - 1832)
• Natural laws are observable.
• They are invariable with time.
Sir Charles Lyell (1797 – 1875)
Lyell's contribution essentially was to make geology an empirical science, distinct from
religious cosmology.
 He followed the principles of Empiricism and Induction.
• The observation of FACT! if something is empirical, it means it is based on observation or
experience. Geologists were observing layers of rock and fossils.
• From facts, he induced conclusions and hypotheses- but only if they fit the facts. (Specific
results to general principle)