Development of the Evolutionary Thought

• Evolution is:

  • Descent with modification; the idea that living species are descendants of ancestral species that were different from the present-day ones
  • Change in the genetic composition of a population from generation to generation
  • Gradual change over time
  • Heavily relies on the inherent variation in the population
• In single-celled organisms, substances can easily enter the cell due to a short distance, while in multicellular organisms, the distance is larger due to a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen due to their higher surface area to volume ratio
• History of Evolutionary Thought:

  • Carolus "Carl" Linnaeus: Father of taxonomy, started the binomial system of nomenclature
  • Thomas Malthus: Believed in population growth leading to competition due to limited resources
  • Georges Cuvier: Studied fossils, opposed evolution, proposed catastrophism
  • James Hutton: Father of Modern Geology, proposed gradualism
  • Charles Lyell: Worked with Hutton on uniformitarianism
  • Jean Baptiste de Lamarck: Proposed Lamarckian evolution theories
• Jean Baptiste de Lamarck's Theories:

  • Theory of inheritance of acquired traits
  • Theory of use and disuse
  • Physiological needs drive Lamarckian evolution
  • Defined evolution as a process of increasing complexity
  • Believed in no extinction of species, but rather evolution into different species
  • Organisms adapt to evolve
• Charles Darwin:

  • Explained evolution through Natural Selection, Idea of Common Descent, Idea of Gradualism, Idea of Multiplication of species
  • Published "On the Origin of Species by Means of Natural Selection"
  • Conducted a scientific expedition on the HMS Beagle in 1831
  • Organisms evolve to adapt
• Alfred Russel Wallace:

  • Corresponded with Darwin on evolution by natural selection
  • Realized that species evolved due to the survival and reproduction of the fittest individuals
• Four Main Ideas on Darwin's Theory of Evolution:

  • Variations in the Population
  • Inheritance of traits
  • Competition amongst offspring
  • Survival of the fittest
• Tenets of Darwinian Theory of Evolution:

  • Common Descent: Diversity of life emerged from one or a few common ancestors
  • Gradualism: Evolution occurs in innumerable small steps
  • Speciation: Formation of new species via reproductive isolation
  • Natural Selection: Competition leads to the survival and reproduction of the fittest
• Drivers of Evolution:

  • Darwin and Wallace did not account for genetic variation as a driver of evolution
  • Anything that influences variation drives evolution