History of Evolutionary Thought - Evolutionary Biology - Lecture Notes, Study notes of Evolutionary biology

Download History of Evolutionary Thought - Evolutionary Biology - Lecture Notes and more Study notes Evolutionary biology in PDF only on Docsity! 1 The History of Evolutionary Thought I. History of evolutionary thought. A. Herakleitos (ca. 500 BC) believed the universe was in constant state of flux. B. Plato and idealism. Also known as Typology, or essentialism 1. Major concept: Every object formed around a perfect essence or type. Also called idealism a. Called ειδοσ. (eidos) Root of 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. 2. If variation is just based on our flawed sensory perception of the "real" world, then evolutionary mechanisms (e.g. natural selection) that depend on variation are ineffective. 3. Still persists in biology. a. When a new species is described, a specimen is placed in museum and is designated as the "type" specimen. b. Molecular biologists often refer to THE DNA sequence of a gene (or even to THE human genome). . C. Aristotle also contributed his ideas to the static view of nature. 1. Major concept: Scala naturae = "Great chain of being" a. The scala naturae was consistent with Platonic typology - species are fixed and do not evolve. 2. This was the dominant idea organizing biology for 2000 years until the 18th century. There are still remnants of this today - we talk of fishes as "lower vertebrates", and mammals as "higher" vertebrates. 3. Scala naturae promoted by Herder (1744-1803) and adopted by Goethe (1749-1832), who felt that the creation of each level of organism was based on a fundamental primitive plan – an archetype or Bauplan. D. Explaining gaps in the Great Chain of Being. 1. Voltaire (1694-1778) was perhaps one of the first to dispute the concept of such a hierarchy. 2. Questioned 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. a. He proposed that such gaps were the result of extinctions. b. In this manner, he echoed the thoughts of other philosophers; Descartes (1596-1650) and Leibniz (1646- 1716). 2. Leibniz suggested that such gaps might not only be due to extinction, but to the transformation of species. 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). 3. Such progress toward perfection fitted nicely with the thinking of Boneet (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.] 4. There was also a great search to find the multitude of living organisms that many felt would be found to occupy all the various rungs of the Ladder. II. The fixity of species was incorporated into Judeo-Christian thought. A. Nature came to be studied "for the greater glory of God" 1. The natural theology, that the path to God was through contemplation of his works -began to grow, and was to flourish until the 1800's. B. Carolus Linneaus (1707-1788) - ironically, laid important groundwork for Darwin. (Actually Swedish botanist by the name Karl von Linné, but wrote under the Latin name.) 1. Founder of modern systematics (the classification of living things). 2. Wrote Systema naturae - described and classified ALL known species of plants and - over 11,000 species). 3. Invented the hierarchical classification scheme we still use today. 4. His view was based on Plato and Aristotle - every individual is the imperfect reflection of an immutable heavenly type. Docsity.com 2 a. Classification scheme developed only to reveal God's plan 5. Overtime, Linnaeus revealed, in a limited fashion, that species might change over time. a. The phrase "no new species can arise," found in earlier editions of the Systema Naturae, disappeared in later editions. III. Pre-Darwinian proponents of evolution. A. Erasmus Darwin (Charles’grandfather) formulated one of the first formal theories on evolution in Zoonomia, or, The Laws of Organic Life (1794-1796). B. Buffon (1707-1788) Histoire Naturelle. 100 years before Charles Darwin 3. This was a 44 volume encyclopedia describing everything known about the natural world, wrestled with the similarities of humans and apes and even talked about common ancestry of Man and apes. 2. Buffon mentioned many concepts that Darwin was to use: competition, variation, and extinction. He also echoed the idea that species were not immutable- but he never pulled it all together. No mechanism. 3. In fact, Buffon, who had proposed evolutionary events on the cosmological and geological levels talked himself out of evolution at the biological level. a. New species had not appeared during recorded history. b. Matings between different species led to either inviability or sterility of the hybrids (think horses). c. Where are all the missing links between existing species if transformation has taken place? d. It was contrary to religion. C. Jean-Baptiste Lamarck (1744-1829). 1. Lamarck sought to deal with the shortcomings that Buffon found by doing away with the reality of species. e. Lamarck proposed that species distinctions were artificial and arbitrary, although useful for classification. b. Lamarck could not accept extinction, thus he accounted for the disappearance of an organism through its evolution into the next "higher form" on the Scala Naturae, which now became an escalator! 2. Philosophie Zoologique (1809) was most important and influential pre-Darwinian work on evolution. Two basic ideas: a. Teleology - innate striving of organisms toward perfection, as organisms attained perfection, they became better and better adapted to their environments. b. Inheritance of acquired characteristics. The modification organism acquired during its lifetime could be passed along to its offspring. (Also known as the effects of use and disuse). 3. Mechanism is of course wrong - acquired characters aren't inherited. BUT it was a progressive theory. It was important because: a. It proposed that species changed through time and b. More importantly, it provided a mechanism to explain how. (Thus, it could be tested.) f. His approach - LOGICAL DEDUCTION- Specific prediction from a general explanation. The inheritance of acquired characteristics could explain changes in individual species. IV. Contributions from geology. A. Evolutionary theories (including Darwin's) were heavily influenced by geology. Two schools of geological thought emerged during the 18th and 19th centuries - catastrophism and uniformitarianism. B. Catastrophism - Belief that Earth primarily formed during rare catastrophic events. 1. Proponents – paleontologist, George Cuvier (1769-1832) and naturalist Louis Agassiz (1807-1873). a. Cuvier was a serious and effective opponent to the evolutionists of his day. 2. Catastrophism was consistent with Christian dogma - Biblical creation. a. Multiply strata indicated many catastrophes. b. Appearance of new species in younger rock from species immigrating from other areas. C. Uniformitarianism expansion of gradualism. Earth was shaped by processes that can be observed today (e.g., erosion, sedimentation, volcanism) acting over immeasurably long periods of time. Geological process must balance out: processes that build mountains are eventually balanced out by erosion. 1. Proposed by Scottish farmer and scientist James Hutton (1726-1797). Docsity.com