History of Evolutionary Thought

History of Evolutionary Thought

Contributions of Past Scientists

• Georges-Louis Leclerc was a French naturalist
• Leclerc worked on a 44-volume Natural History series describing plants and animals
• Leclerc provided evidence of evolution and proposed various causes

Carolus Linnaeus

• Linnaeus was a Swedish botanist
• He developed the Binomial System of Nomenclature
• Also developed a system of classification for living organisms
• Linnaeus believed in scala naturae and the fixity of species

Erasmus Darwin

• Darwin was a British physician and naturalist
• He formulated one of the first formal theories on evolution in Zoonamia
• Based his conclusions on changes in animals during development
• Also conclusions were based on animal breeding by humans and vestigial structures

Georges Cuvier

• Cuvier was a French zoologist who established the sciences of comparative anatomy and paleontology
• Cuvier developed a theory of catastrophes, where animal and plant species are destroyed by natural catastrophes
• New species evolve after these catastrophes

James Hutton & Charles Lyell

• Hutton and Lyell developed the concept of Uniformatism
• It explained that Earth's landscapes, including mountains and oceans, formed over a long period through gradual processes

Jean Baptiste Lamarck

• Lamarck was a French biologist
• Best known for the idea that acquired characteristics are inheritable
• Also known as Lamarckism
• Proposed two principles, (1) the law of use and disuse, (2) Inheritance of acquired characteristics
• Lamarck's theory explains the environment can change an organism during its lifetime which can be inherited

Thomas Malthus

• Malthus was an English economist
• Published “An Essay on the Principle of Population,” proposing human population size is limited by available resources
• Charles Darwin used Malthus’ principle to formulate his idea of natural selection

Charles Darwin

• Darwin was an English naturalist
• His scientific theory of evolution by natural selection became the foundation of modern evolutionary studies
• Formulated the theory after returning from his voyage and wrote “On the Origin of Species”

Darwin's Theory of Evolution

• On the voyage of the Beagle, Darwin studied life and geology throughout the world
• Many of Darwin's ideas about natural selection and evolution originated from observations on the Galápagos Islands
• Darwin observed massive geological changes and Earth's massive geological changes came from slow processes
• Earth must be very old
• Darwin gathered fossil specimens that differed from modern species, for example Glyptodon, an armadillo-like animal

Biogeographical Observations

• Animals on different continents differed but in similar environments had similar-looking animals
• Darwin speculated whether each Galápagos tortoise type descended from a common ancestor
• Long-necked tortoises in dry areas where low-growing vegetation was scarce, but short-necked tortoises in moist regions
• Darwin observed that finches exhibited significant variation in beak size and shape
• He speculated that a mainland finch was the common ancestor in the Galápagos Islands

Publication of “On the Origin of Species”

• Darwin received a manuscript from British naturalist Alfred Russel Wallace
• Wallace collected and identified thousands of species in the Malay Archipelago for 8 years

Natural Selection and Adaptation

• Individuals in a species differ and variation is heritable
• Essential resources like food and space are limited
• Populations produce more offspring than can survive
• Darwin realized that the capacity to overproduce was characteristic of all species

Modern Synthesis

• Modern evolutionary synthesis unifies DNA, mutations, inheritance, and natural selection
• Genes are responsible for hereditary characteristics
• Populations NOT individuals, evolve by natural selection and genetic drift
• Speciation occurs due to accumulation of small genetic changes

Microevolution

• Evolution is a change in the frequency of a gene in a population
• Microevolution is evolutionary change within a population
• Five forces can shift genes

Causes of Microevolution

• Variation exists; members of a population differ
• Increased fitness makes individuals better adapted to their environment
• Individuals that are better adapted are more likely to reproduce
• Survival traits are passed down from generation

Natural Selection

• Natural selection is the ability to adapt & increased chance of survival

Types of Selection

• Directional selection: one certain phenotype is favored
• Disruptive selection: two phenotypes are favored
• Stabilizing selection: intermediate phenotype is favored
• If disruptive selection favors small or large rather than medium, stabilizing selection favors medium
• Sexual selection: adaptive changes give higher chances of finding a mate
  • Intrasexual = self
  • Intersexual = with another

Mutation

• Mutation is a random change in the genetic sequence of a living thing's DNA
• A change in base, may create an entirely different amino acid
• Anything with RNA or DNA can have mutations, such as animals, humans, plants, bacteria, and fungi
• Mutations do not all affect the genetic equilibrium of a population

Gene Flow (Migration)

• Gene flow is movement of alleles between populations
• When gene flow brings a new or rare allele, the allele frequency changes

Genetic Drift (By Chance)

• Changes in allele frequencies of a gene pool are due to chance effects
• Such events remove individuals & their genes, from a population at random

Types of Genetic Drift

• Bottleneck effect: loss of genetic diversity due to natural disasters, disease, overhunting, overharvesting, or habitat loss
• Founder effect: genetic variation is lost when a few individuals break away from a large population to found a new population

Non-Random Mating (Preference)

• Affects how alleles assort into genotypes
• Assortative mating: similar individuals mate more frequently
• Dissortative mating: dissimilar individuals mate more frequently

The Hardy-Weinberg Principle

• A population with allele frequencies that do not change over time is in genetic equilibrium (HWE)
• Assumes that the genetic pool of the parent stays the same if there are no external forces
  • No natural selection, mutation, or migration
  • No large population or random mating

Terminologies

• Gene pool: the combination of all genes in a reproducing population or species
  • A large gene pool has better genomic diversity to withstand challenges
• Gene/allele frequency: relatives frequency of an allele (variant of a gene) at a locus
• Genotype frequency: fraction of individuals with a given genotype
• Phenotype frequency: fraction of individuals with a given phenotype
• Alleles formula equation: p + q = 1
• Genotypes formula equation: p² + 2pq + q² = 1

Macroevolution

• Darwin's finches: Darwin's voyage to the Galapagos Islands led him to observe diverse finches
• Macroevolution is patterns and processes of evolutionary change at the species level
• It results in speciation, or formation of new species
• Speciation occurs when some members of a population can no longer interbreed

Patterns of Macroevolution

• Divergent evolution: interbreeding species diverge into two or more groups & is caused changes in the environment or migration
• Convergent evolution: distinctly different species become more similar in structure and function because they live in similar environment
• Parallel evolution: species descended from a common ancestor develop similar traits they adapt to similar environmental changes
• Co-evolution: one species changes, the other changes in response so the relationship can continue

Reproductive Isolating Mechanisms

• Pre-zygotic isolation occurs before formation of a zygote
• In general they prevent reproductive attempts
• Make fertilization unlikely is mating occurs

Types of Pre-Zygotic Isolation

• Habitat isolation: species occupy different habitats in a geographic range, so are less likely to meet and attempt to reproduce
• Temporal isolation: species can live in the same locale, but they reproduce at different times so do not mate at all
• Behavioral isolation: courtship patterns attract mates or other species, these are effective even with related species
• Mechanical isolation: animal genitalia structures or plant floral structures are incompatible so reproduction can not occur
• Gametic isolation: gametes of two different species meet, they still may not fuse to become a zygote

Post-Zygotic Isolation

• Occurs after the formation of the zygote
  • Hybrid inviability: genes of parent species interact that impairs development or survival
  • Some salamanders in the same range can interbreed
  • Hybrid sterility: hybrid zygote sterile adult, chromosomes differ the in number structure & may fail to produce normal gametes
• Hybrid breakdown: first-generation hybrids are viable and fertile, but when they mate with one another or with either parent species, offspring of the next generation are feeble for sterility

Modes of Speciation

• Allopatric speciation: new species forms when a geographic barrier physically separates & it cannot interbreed
• Parapatric speciation: two populations live in neighboring areas & share a border zone
• Sympatric speciation: population develops into two reproductively isolated groups without geographic isolation

Evidence of Evolution

• Fossil record: Fossils are remains of organisms that lived long ago which are found in sedimentary rock
• The deeper the sediment of the rock, the older the fossils remain

Fossil Formation

• Compression: fossils of a leaf preserves part of the plant
• Petrifications: human ancestors fossils consist of mineralized bone, fossils are found in portions
• Impression: fossil reveal footprint of anatomical details

Types of Fossils

• Cast: the horn coral is a cast & organic compound material is replaced
• Intact preservation: fossils get preserved intact in tree resin (amber)

Transitional Fossils

• Bears a resemblance to two groups which are classified separately

Fossil Record Completion

• Because there is no traces for fossils, plates are constantly moving

Biogeographical Evidence

• Biogeography is study of geological distribution of fossils animals
• Cases of missing Marsupials

Wallace’s Line

• Alfred Russel Wallace traveled the Malay Archipelago and noted animal on boundary side

Anatomical Evidence

• Homologous structures: structures set with bones that that evolved from common ancestors
• Analogous structures: structures that perform the same function
• Vestigial structures: anatomical structure that are developed but are nonfunctional

Evolutionary Embryology

• Embryology is the development animal from a embryo to adult
• Share the common structures in embryo stage

Lynncean Taxonomy

• Carolas Linsaeaus devised a way to organize a scheme of classification

Linnaean Classification

• Lynnaues grouped that are organized

Taxonomic Scale

• Arrcheca, bacteria, eucarya are inclusive scales in domain
• Then kingdoms, phylums
• The second format is name common with binomial

Dichotomous Key

• Identification where have 2 categories repeatedly

Diagrammatic Relationship

• A common pair laid out for number sequence
• Describes the diagrams of ancestors
• Tree indicate ancestors decent of lineage