Pre-Darwinian Evolutionary Thought

History of Evolutionary Theory

• Pre-Darwinian views, Darwin, Neo-Darwinian thinking are topics covered
• Evaluation of the course includes Term Test I, Term Test II, and Final Exam

Evolution

• Evolution is systematic change through time
• Organisms undergo biological change, and social systems undergo cultural change
• The idea of evolution suggests that modern life forms originated from other species in the past, rather than being independently created
• Evolution allows for the concept of change

Pre-Darwinian Views of the Natural World

• Perceptions on Variation and Change in the natural world include Essentialism, Great Chain of Being, Catastrophism & Uniformitarianism, Transformational Evolution
• Key concept: Essentialism. Traced to Plato, fixed forms exist perfectly and unchanging, differences not affecting unchanging essence. Aristotle elaborated on this with similarities and differences organizing life into a single line
• Great Chain of Being. Framework for interpreting the world, all organisms linked in a single chain, no gaps, flexibility or extinction. Organisms ranked from least possible difference, with humans divinely ideal.
• Catastrophism & Uniformitarianism. Cuvier proposed catastrophism, where fossil species repeatedly wiped out and replaced by new ones. Lyell proposed uniformitarianism, which emphasizes that natural forces were constant in the past and present-day.
• Transformational Evolution. Lamarck understood the world could change, did not believe in fixed unchanging organisms. He explored mechanisms for biological change.

Carolus Linnaeus (1707-1778)

• Modern biological taxonomy (classification)
• Essentialist, number of species created fixed and unchanging.
• Based classifications on similarities and differences amongst species
• Recognized close relationships, e.g., humans, apes, monkeys
• Recognized humans as part of nature which was controversial at the time

Modern Taxonomy based on Linnaean Classification

• Kingdom (Anamalia), Phylum (Chordata), Class (Mammalia), Order (Primates), Family (Hominidae), Genus (Homo), Species (sapiens)
• Anatomically modern humans: Homo sapiens sapiens
• Reproductively Isolated

Georges Cuvier (1769-1832)

• Pioneer in palaeontology, important excavations of fossils in Seine River Basin - new forms of diversity.
• Proposed catastrophism explaining how to explain new forms of diversity
• Cuvier never argued for one species emerging from another species

Catastrophism

• Fossil species repeatedly wiped out and replaced by new species
• A concept of "revolutions" such as natural disasters (e.g., floods)
• New species created when others were destroyed; creation might appear disorderly and arbitrary

Charles Lyell (1797-1875)

• Scottish geologist
• Stimulated interest in the idea of Uniformitarianism in the 19th century.

Lyell & Uniformitarianism

• Natural forces constantly reshaping earth.
• Change in organisms like cyclic changes in seasons and geology.
• Catastrophism falls out of favour, and uniformitarianism gains more acceptance.
• Shaped Darwin's ideas

Jean Baptiste de Lamarck (1744-1829)

• Understood the world could change
• Did not believe in fixed unchanging organisms/ Essentialism
• Explored mechanisms for how biological change could occur, and developed idea of transformational evolution
• Two ways: Law of use and disuse: features strengthened/enhanced by use or weakened/disappeared through disuse. Also, Law of inheritance of acquired characteristics
• Noted fossil species resembling living species suggested ancestors. Fossils looked different due to climate/geography.

Lamarck (continued)

• Argued the Creator provided species with the ability to change.

Charles Darwin (1809-1882) & Alfred Russel Wallace (1823-1913)

• Darwin's journey on HMS Beagle (1831-36) and Wallace's travels in S. America
• Observing variations (species diversity)
• Species emerge through descent with modification from a single parental population
• Darwin's book: On the Origin of Species by Means of Natural Selection or Preservation of Favoured Races in the Struggle for Life published in 1859.

Darwin - Background

• Lyell's Principles of Geology (1831)
• Darwin's observations of artificial selection in breeders, gardeners of pigeons
• Competition for scarce resources (Malthus' Essay on the Principle of Population - 1838)

Thomas Malthus (1766-1834)

• English clergyman and political economist concerned with decline of living conditions
• Conflict for life, geometric reproduction (e.g., 2, 4, 8), resources increase arithmetically (e.g., 1, 2, 3), famine and poverty

Darwin's Contributions...

• Theory of Natural Selection, or Variational Evolution: Biological variation exists in populations. Best suited/adapted to the current environment have a better chance of survival and reproduction, passing genes.
• Unlike Lamarck: environmental change didn't cause variation, variation pre-exists.
• Natural Selection isn't purposeful.
• No genetic understanding of how variation exists

Gregor Mendel (1822-1884)

• Austrian monk/botanist, studied pea plants (phenotypes)
• Contributed to the concept of transmission of inheritance, or genetics, origins – phenotypes, not genotypes.
• Published 1866

After Mendel...

• Genes = segments of DNA, building blocks of proteins
• Alleles = alternative forms of a gene
• Homologous chromosomes (23 pairs, 46 chromosomes total)

Chromosomes

• Pair of homologous chromosomes
• Gene locus (gene location)
• Allele pair (alternate forms of a gene)
• New Genetic Combinations in Offspring: Variation through Sexual Reproduction
• Gametes contain only a sample of parents' genetic makeup; meiosis producing gametes with 23 chromosomes. Gametes combining create 46 chromosomes in offspring, leading to variety.

Evolutionary Forces and Factors

• Mutation, a change in genetic material creating new variation. Rare, but significant within populations.
• Gene Flow, involves movement of genes/alleles between populations via migration and interbreeding. Decreases genetic differences.
• Random Genetic Drift impacts small populations - genes become more/less common due to chance events. Examples: Founder Effect, Bottleneck; both restrict the gene pool of future generations
• Natural Selection, a slow process reshaping populations, with the survival/reproduction of certain variants. Differential mortality and fertility.

Human Populations - A Life Course Perspective

• Survival and differential mortality.
• Reproduction and differential fertility

Natural Selection (continued)

• Mutation, gene flow, and genetic drift may influence what genes are present in populations.
• Natural selection provides directional change in gene frequencies, with alleles becoming more/less common.
• Changing environments affect selection pressures, and certain alleles become more/less adaptive.

Karl Landsteiner (1868-1943)

• Austrian physician
• Identified the ABO blood group system
• Model of Mendelian inheritance (alleles at one genetic locus).

Aspects of the ABO System

• 3 alleles (A, B, O)
• 6 genotypes (AA, AO, BB, BO, AB, OO)
• 4 phenotypes (A, B, AB, O)

Punnett Square - Genes in Families

• Biological father & mother alleles combinations

Genes in Populations

• Global allele frequencies (O, A, B)
• Variations in clinal and distinct allele distributions
• Natural Selection in relation to allele global distributions.
• Smallpox and reduced frequencies of A alleles in certain areas.
• Variation in antigens of red blood cells.

How to Interpret Global Distribution of A, B, and O alleles

• Mutation
• Gene Flow
• Random genetic drift
• Founder effects and bottlenecks
• Natural Selection (differential mortality example: Smallpox)

Explore pre-Darwinian ideas about evolution, including essentialism, the Great Chain of Being, and contributions from Linnaeus and Cuvier. Review transformational vs variational perspectives and classification. Learn how exploration shaped evolutionary thought.