Presentation on theme: "The History of Evolutionary Thought Today: begin consideration of evolution with historical overview. Reasons: 1.See how Darwin and others arrived at their."— Presentation transcript:
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’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.” Aristotle 384 BCE – 322 BCE
Explaining gaps in the Great Chain of Being Voltaire ( ) 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 ( ) and Leibniz ( ).
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 ( ), 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, …how life evolved from a single common ancestor, forming “one living filament”
Pre-Darwinian proponents of evolution Buffon 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.
Jean Baptiste Lamarck ( ). 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. Pre-Darwinian proponents of evolution
Jean Baptiste Lamarck ( ). Pre-Darwinian proponents of evolution Lamarck could not accept extinction, so the Scala Naturae now becomes an escalator!
Jean Baptiste Lamarck ( ). Proponent of two main principles 1.Use and disuse – features that are used are accentuated and features that are not used deteriorate. 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? Pre-Darwinian proponents of evolution
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 ( ). 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. Sir Charles Lyell (1797 – 1875) Principles of Geology ( ) Natural laws are observable. They are invariable with time. 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)