Development of Evolutionary Concepts

• Evolution can be divided into microevolution and macroevolution
• Microevolution deals with processes, while macroevolution concerns history

Development of Evolutionary Concepts

• The development of evolutionary concepts is a topic within genetics

Evolution Before Darwin

• Aristotle believed in "Scala Naturae," a "Great chain of being" or a scale/ladder of nature
• In Scala Naturae, there was ordered gradation from inanimate to barely animate organisms up to higher life forms
• Linnaeus, in his 1735 publication "Systema Naturae", introduced binomial classification (modern taxonomy)
• Linnaeus classified "related" species into genera, "related" genera into orders, and so on
• Linnaeus viewed the "relatedness" as a design of the Creator
• Lamarck, in his 1809 publication "Philosophie Zoologique", suggested species change through time, but with no extinction
• Lamarck also proposed the inheritance of acquired characteristics, which is not correct

18th Century European Thought

• People thought the Earth was thousands of years old
• People believed that species were created as they currently appear and never changed
• Many thought everything ever created still existed and could be found somewhere on Earth
• Adaptations were believed to be produced by divine intervention

The Historical Setting by 1859

• People realized the Earth was very, very old, as indicated by the work of Charles Lyell (1810-33)
• Fossils represented extinct species, as shown by Baron George Cuvier (1807-32)
• Existing species are descended from shared ancestors (Étienne Geoffroy Saint-Hilaire with Cuvier, 1830)
• Adaptations are produced by natural selection (Charles Darwin in notes from 1838)

1835 Chile Quake

• Darwin collected evidence of coastal uplift during the earthquake, discovering marine shells inland
• This evidence supported the idea that small uplifts occurred repeatedly over geological time
• Darwin was convinced by Charles Lyell's idea that mountain chains grew almost imperceptibly over time
• Darwin connected earthquake, volcano and crustal movement phenomena
• Darwin’s findings later influenced him to ask how living things adapted to an ever-changing world
• Darwin concluded "this large portion of the earth's crust floats in a like manner on a sea of molten rock"
• Darwin hypothesized that new species were descendants of earlier ones, adapted by natural selection

Darwin & Wallace

• Darwin spent 5 years on HMS Beagle (1831-1836)
• Darwin, on September 28, 1838, at 29 years old, made the connection between Malthus and organisms

Thomas Robert Malthus

• Thomas Robert Malthus anonymously published "An Essay on the Principle of Population" in 1798
• He predicted population would increase geometrically, doubling every 25 years, while food production grew arithmetically
• Darwin and Alfred Russel Wallace cited Malthus as key to developing the theory of natural selection
• In October 1838 after reading Malthus’ “Population”, Darwin appreciated the struggle for existence
• Darwin made the connection that favorable variations would be preserved, and unfavorable ones destroyed

Darwin & Natural Selection

• Two major ideas: all species have descended without interruption from one original form of life
• If useful variations occur, those individuals will have the best chance of surviving and producing similar offspring

After Darwin

• Darwin’s big problem was lack of the mechanism for heritable variation
• Mendel's peas could have been a solution (1863), but they were not discovered until 1900
• Discovery of mutations led to notions of large-scale evolution by jumps (saltation)
• Evolution by jumps pitted geneticists against Darwinists
• Two conceptual advances reconciled Mendelism and Darwinism into neo-Darwinism
• Neo-Darwinism: evolution occurs by natural selection and not acquired characters
• In 1908, the Hardy-Weinberg law was discovered for calculating gene frequencies under natural selection
• In 1918, R. A. Fisher's paper correlated relatives on the supposition of Mendelian inheritance

The Modern Synthesis of Evolution

• In the 1930s, the applications of the Hardy-Weinberg equation and R.A. Fisher led to the rise of population genetics
• Population genetics studies the changes in gene frequency within a population under selection, mutation, genetic drift, and gene flow
• In the 1940s, the synthesis of population genetics, systematics, and adaptive change yielded the "Modern Synthesis"
• According to Futuyma, organisms exist as individuals, and individuals exist in populations
• Natural selection acts on individuals but individuals do not evolve
• Populations include different age classes and generations.
• Sexually reproducing populations have non-identical individuals
• Populations don't reproduce; individuals do. Resources are limited
• Variation is essential for evolution; natural selection allows some variants to survive
• Differential reproduction results in survival of the best-suited individuals
• Genetic background differs in sexually reproducing organisms, influencing gene inheritance
• Genetic composition changes gradually due to differential reproduction, mutations, and gene exchange
• Populations may subdivide, reinforcing genetic differences leading to speciation
• Populations may crash or become extinct

Modern Synthesis: Futuyma's 20 Main Points

• Phenotype is influenced by genotype and environment
• Environmental effects are generally not inherited
• Heredity is governed by discrete genes
• Genes can mutate to form new alleles
• The environment does not bias mutations
• Evolution is a population process (change in genotype/allele frequencies)
• Changes in frequencies can be due to drift or selection
• Small selective differences matter
• Selection can alter populations beyond original variation due to recombination between alleles
• Natural populations are genetically variable
• Geographic differences can have a genetic basis
• Phenotypic differences often arise from the cumulative effect of many small genetic changes
• Natural selection continues to act today
• Geographic differences are often adaptive
• Phenotypic differentiation can occur within a species; species represent distinct gene pools
• The degree of differentiation lies on a continuum
• Speciation is often linked with geographic isolation
• Differences between higher taxa are the sum of many small differences
• Gaps in the fossil record occur due to incompleteness, but also show intermediate forms
• Paleontology aligns with evolutionary theory