Darwinian Evolution and Geological Time

Concepts of Evolution

• Chapters cover evolution, specifically focusing on human evolution.
• The text references chapters 13, 14, 15, and 19.

Darwin's Theory of Evolution

• Charles Darwin is considered the "Father of Evolution."
• Darwin's childhood and education are discussed.
• The conventional view at the time was that species were fixed.
• The Judeo-Christian belief system interpreted the Genesis account literally, estimating Earth's age at 6,000 years.
• At 22 years old, Darwin embarked on a voyage.

Darwin's Sea Voyage

• Darwin's exploration focused on collecting fossils and living organisms.
• Detailed observations of species and their environments were recorded.
• Geographic proximity was more informative regarding species relationships than environmental similarity.
• Fossils from South America resembled living species in the same region.
• Evidence of extinct armadillo fossils resembled living armadillos.

Darwin's Writings

• Darwin doubted the Earth's age was only a few thousand years.
• He concluded that the present species were descendants of ancient species.
• Darwin hypothesized that descendants spread and accumulated adaptations that fitted them to their specific environments.
• Darwin wrote an essay on natural selection and delayed publication.
• He published "The Origin of Species" after learning Alfred Wallace had a similar hypothesis.

The Study of Fossils

• Fossils are imprints or remnants of organisms.
• Some fossils are not actual remnants but evidence of organisms.
• Types of fossils include casts, imprints, hard parts like teeth and bones, coprolites (fossilized feces), and amber-trapped insects.

Transitional Forms

• Fossils link past species to the present.
• Paleontologists found transitional fossils, suggesting whales evolved from a wolf-like carnivore.
• Molecular similarities were identified between whales and hippos, hinting at a cloven-hoofed ancestor.
• Pakicetus and Rodhocetus fossils demonstrated a cloven-hoofed mammal ankle bone.

Homologies

• Evolution describes descent with modifications.
• Evolution is a remodeling process.
• Related species can have characteristics with underlying similarities but function differently.
• Common ancestry is reflected in homology.
• Structural and molecular homologies reveal evolutionary relationships.

Vestigial Structures

• Vestigial structures are remnants of structures of marginal or no importance to the organism
• Examples include small pelvis and hind-leg bones in ancient whales that are remnants.
• The eye remnants located beneath scales show the persistence of a feature.

Homologies and Evolutionary Trees

• Evolutionary trees are hypotheses of evolutionary descent
• Some trees rely predominantly on fossil, anatomical, and molecular data.
• Some trees are based on speculation.

Natural Selection

• All domesticated plants and animals are products of selective breeding.
• Artificial selection is selective breeding to create desirable traits.
• Organisms tend to overproduce offspring, leading to competition for resources.
• Organisms with beneficial adaptations survive and reproduce more successfully, passing on these adaptations.
• Natural selection "selects" the fit for survival.

Three Key Points about Evolution

• Organisms do not evolve individually; it is the population that evolves over time.
• Natural selection can only amplify or reduce heritable traits.
• Evolution is not goal-directed; it does not lead to perfectly adapted organisms.

Observing Natural Selection

• A plane spraying pesticides on crops highlights pesticide resistance in pests.
• Pests with resistance survive and reproduce; resistant insects increase in frequency.

The Evolution of Populations

• Individual variation is common across an organism.
• Mutations generate variations needed for the evolution process.
• Genetic variation in sexually reproducing organisms arises from unique allele combinations, due to independent events.
• Recombination of genes drives variability among offspring.

The Hardy-Weinberg Equation

• The Hardy-Weinberg equilibrium equation assesses whether a population's allele and genotype frequencies remain constant over generations.
• Equilibrium requires a large population, random mating, no mutation, no gene flow, and no natural selection

Natural Selection, Genetic Drift, and Gene Flow

• Natural selection, genetic drift, and gene flow are evolutionary changes' drivers.
• The bottleneck effect creates a smaller, genetically diverse population.
• The founder effect is seen in populations isolated from the original parent population.
• Gene flow reduces differences between populations by transferring alleles.

Natural Selection and Adaptive Evolution

• Natural selection is the only consistently occurring mechanism that drives adaptive evolution.
• Adaptive evolution occurs when organisms and their environment complement each other to drive survival.
• Relative fitness relates to an organism's contribution to the next generation's gene pool relative to other organisms in the population

Natural Selection and Variation

• Stabilizing selection favors intermediate phenotypes.
• Directional selection affects the overall makeup of the population by acting against one extreme phenotype.
• Disruptive selection typically arises when environmental conditions favor both extremes of a phenotype.

Sexual Selection

• Sexual selection describes how individuals with particular traits are more adept at attracting mates.
• Secondary sexual characteristics give individuals mating advantages.
• Sexual dimorphism involves noticeable differences between males and females unrelated to reproduction.
• Males are often showier than females.

Intrasexual Selection

• Intrasexual selection occurs when individuals compete within the same sex to gain access to mates.
• Competition can involve physical combat or more often ritualized displays.
• Male-male competition is often used to gain supremacy in groups or herds.

Intersexual Selection

• Intersexual selection (mate choice) usually involves individuals of one sex choosing mates.
• Mate choice is typically based on appearance or behavior.

Diploidy and Balancing Selection

• In diploidy, recessive alleles are "hidden" within the population, facilitating population variability.
• Balancing selection maintains stable genotype frequencies where two or more phenotypic forms exist within the population.
• Heterozygote advantage refers to situations where heterozygous individuals are fitter compared to either homozygous state.

Origin of Species

• The Galapagos Islands are home to multiple species of giant tortoises.
• Lonesome George was the last member of his species.
• The biological species concept defines species based on interbreeding.

Speciation

• Microevolution is change to the gene pool in a population through time.
• Speciation results from the division of one species into two or more through time.

Defining Species

• The biological species concept emphasizes reproductive isolation, in which species do no interbreed.
• The morphological species concept identifies species based on observable physical traits.
• The ecological species concept focuses on species' roles in their ecosystem.
• The phylogenetic species concept defines species as the smallest group of individuals sharing common ancestry.

Visualizing the Concept: Reproductive Barriers

• Reproductive barriers isolate species’ gene pools and prevent interbreeding.
• Prezygotic barriers operate before zygote formation, while postzygotic barriers occur after zygote formation.

Allopatric Speciation

• Geographic isolation results in new species.
• In allopatric speciation, physical separation of species results in genetically isolated species as gene pools change due to natural selection, mutation, and genetic drift.

Sympatric Speciation

• Sympatric speciation occurs when new species arise within the same geographic area as the parent species.
• Accidents during cell division can lead to polyploidy. This occurs when a plant develops an extra set of chromosomes.
• Plants that are polyploid cannot interbreed with other diploid species.
• Sympatric speciation is possible through habitat differentiation of the resulting populations.

Isolated Islands

• Islands are known for showcasing speciation events.
• Geographic isolation allows populations to diverge genetically.
• Adaptive radiation is the evolution of many diverse species from a common ancestor.
• The Galapagos Islands and the finch species exemplify adaptive radiation.

Speciation Can Evolve Rapidly or Slowly

• Darwin supported a gradual evolutionary model.
• The punctuated equilibrium model proposes lengthy periods of no evolutionary change interrupted by episodes of rapid evolution.

Conditions On Early Earth

• Evidence suggests the universe began with a massive explosion from a single point (Big Bang).
• Earth formed from a dust cloud around a young sun about 4.6 billion years ago.
• Intense heat from asteroid impacts and compression led to Earth's initial molten state.

Life's Earliest Evidence

• Earliest life evidence comes from fossils from about 3.5 billion years ago.
• Rock formations (stromatolites) were built up by ancient photosynthesizing prokaryotes.
• Likely, life developed as early as 3.9 billion years ago.
• Scientists believe that chemical and physical processes on early Earth created simple cells through four stages:
  • Abiotic synthesis of small organic molecules like amino acids,
  • Joining of small organic molecules into polymers,
  • Packaging polymers into "protocells" with membranes,
  • Origin of self-replicating molecules (RNA).

Experiments on Abiotic Synthesis

• Oparin and Haldane hypothesized that conditions on early Earth could have produced organic molecules.
• Miller and Urey tested the hypothesis in 1953.
• The experiment demonstrated the creation of amino acids, suggesting that abiotic synthesis of organic molecules was plausible.

Major Events in the History of Life

• Earth's history is divided into four eons: Hadean, Archaean, Proterozoic, and Phanerozoic.
• Each eon includes periods with unique evolutionary events.
• Eons are separated by major developmental changes in the evolution of life.

Mass Extinctions

• Five major mass extinction events have significantly altered evolution.
• These events caused significant environmental change and resulted in 50% or greater species extinction rates.
• Mass extinction events drastically change Earth's ecosystems, driving species adaptation.
• The Permian and Cretaceous events are notable, each involving significant ecological changes.

Phylogeny and the Tree of Life

• Taxonomy is the classification of organisms.
• Linnaeus method of scientific naming (binomial nomenclature) uses genus and species names.
• Taxonomy hierarchical structure of domains, kingdoms, phyla, classes, orders, families, genera and species.

Phylogenies

• Evolutionary history of a species is known as phylogeny.
• Systematics classifies organisms and relates them to their evolutionary history.
• Phylogenetic trees are based on homology, depicting evolutionary relationships.
• Data from fossils, morphology, and molecular analysis assists in understanding these relationships.

Cladistics

• In cladistics, organisms are grouped based on shared derived characters (traits unique to a clade).
• A clade represents the ancestor and its descendants.
• Organisms are grouped together on the basis of shared characteristics derived from their common ancestor.

Test your knowledge on Darwin's theories of evolution and the geological time scale. This quiz covers key concepts related to adaptation, evolutionary relationships, and significant periods in Earth's history. Dive into the mechanisms that shaped life on our planet!