Natural and Artificial Selection

Artificial Selection

• Artificial selection is selective breeding, encouraging desirable traits across generations.

Natural Selection

• Natural selection drives evolution, favoring traits that enhance survival and reproduction; these traits are then passed down.
• Natural selection relies on two key observations:
  • Traits are inherited from parent to offspring.
  • More offspring are born than can survive, leading to competition and differential survival.
  • Traits aiding survival accumulate in populations, driving evolution.
• Nature favors traits for survival and reproduction, while artificial selection involves humans choosing desired traits.
• Intersexual selection involves mate choice by one sex, often leading to colorful males and selective females.
• Intrasexual selection involves competition among males for dominance and control over females or breeding territories.

Phenotype Distribution and Selection

• Directional selection favors one extreme phenotype.
• Stabilizing selection favors average phenotypes, reducing extremes.
• Disruptive selection favors both extremes, potentially splitting the population.

Evolutionary Fitness

• Evolutionary fitness is measured by the number of offspring that survive.

Hardy-Weinberg Equations

• p + q = 1: The sum of the frequencies of the dominant allele (p) and the recessive allele (q) for a gene with two alleles equals 1.
• p² + 2pq + q² = 1: This equation describes the genetic makeup of a population, including homozygous dominants (p²), heterozygotes (2pq), and homozygous recessives (q²).

Allele Frequency Consistency

• Allele frequencies remain constant if these conditions are met:
  • Infinitely large population
  • No natural selection
  • Random mating
  • No gene flow
  • No mutations
• Meeting these conditions means the population is not evolving.

Genetic Drift

• Genetic drift is a random change in allele frequencies, especially prominent in small populations.
• Bottleneck effect: A large population reduction due to a non-selective disaster can lead to over or underrepresentation of alleles.
• Founder effect: A small, isolated group establishes a new population with a different gene pool.

Gene Flow

• Gene flow is the movement of alleles between populations.
• Gene flow can alter allele frequencies and reduce genetic differences between populations.

Homologous Structures

• Homologous structures are similar characteristics in different species due to shared ancestry.
• Example: Arm bones across various species.

Adaptive Radiation

• Adaptive radiation occurs when one species evolves into multiple descendant species with unique adaptations.

Evidence for Evolution

• Fossil Record: Reveals changes in organisms over time, using the law of superposition and absolute dating of radioactive isotopes.
• Comparative morphology analyzes the structure of living and extinct organisms.
  • Homology: Similar characteristics in related species, despite functional differences.
  • Embryonic homology: Similar embryonic development across species.
  • Vestigial structures: Conserved structures with no current function.
  • Molecular homology: Shared ancestry indicated by molecular structure and monomer sequence.
  • Convergent evolution: Distantly related organisms evolve similar adaptations because of comparable environments
  • Analogous structures: Similar structures with separate evolutionary origins, like wings in birds, bats, and bees.
• Biogeography: The geographic distribution of species. Species on oceanic islands often resemble mainland species.
• Homologous traits: Traits sharing a common underlying structure and embryological origin reflect descent with modification from a common ancestor.

Pseudogenes

• Pseudogenes are nonfunctional gene variants providing evidence for evolution.

Eukaryotic Origins

• Features indicating a single origin for all eukaryotes:
  • Nucleus
  • Mitochondria
  • Endomembrane system
  • Genes with introns
  • Linear chromosomes
  • Sexual reproduction with gamete fusion

Species Definition

• A species can naturally breed and produce fertile offspring and is reproductively isolated from other groups.
• This definition is not absolute; closely related species may produce hybrids.

Isolating Mechanisms

• Isolating mechanisms maintain separate gene pools between species.

Prezygotic Barriers

• Prezygotic barriers prevent mating or fertilization:
  • Behavioral isolation: Unique behaviors separate species.
  • Temporal isolation: Species breed at different times.
  • Mechanical isolation: Reproductive anatomy is incompatible.
  • Habitat isolation: Species live in different habitats.
  • Gametic isolation: Gamete incompatibility prevents fusion.

Postzygotic Barriers

• Postzygotic barriers prevent viable, fertile offspring:
  • Hybrid viability: Incompatible genes impair development.
  • Hybrid fertility: Hybrids cannot reproduce.
  • Hybrid breakdown: Later-generation hybrids are infertile.

Speciation Models

• Allopatric speciation occurs when a geographic barrier separates a species, leading to genetic divergence and reproductive isolation.
• Sympatric speciation occurs without a geographic barrier, potentially through polyploidy in plants, or adaptations to specific microhabitats in animals.

Adaptive Radiation

• Adaptive radiation involves one species giving rise to multiple descendant species with unique adaptations.
• Phylogeny reflects adaptive radiation, homologous traits, and vestigial traits.
• Natural selection acts on phenotypes; advantageous traits increase survival and reproduction.
• Variation is essential for natural selection and adaptation.

Maintaining Membrane Fluidity

• Variations in phospholipid structure, like unsaturated fatty acids, maintain membrane fluidity in cold conditions.

Extinction Process

• The process leading to extinction involves:
  • Small, isolated population
  • Genetic drift and inbreeding
  • Loss of genetic diversity
  • Reduced fitness and adaptability
  • Less reproduction and higher mortality
  • Smaller population, restarting the cycle

Biodiversity Decline

• Humans contribute to declining biodiversity through habitat destruction, overhunting, and introducing invasive species.

Phylogeny

• Phylogeny represents evolutionary history.
• A clade is a group of organisms with a common ancestor.
• A node is where lineages diverge, representing a common ancestor.
• Sister groups are lineages that split from the same node.
• Outgroups are distantly related to determine evolutionary relationships.

Phylogenetic Groups

• Monophyletic group: Includes a common ancestor and all descendants (clade).
• Paraphyletic group: Includes a common ancestor but not all descendants.
• Polyphyletic group: Excludes the most recent common ancestor of all members.
• Sister taxa share an immediate common ancestor and branch from the same node.
• A basal taxon diverged early and remains relatively unchanged.

Origin of Life

• Earth formed around 4.6 billion years ago; life appeared by 3.9 billion years ago.
• Early Earth had inorganic molecules.
• Oparin and Haldane: The early atmosphere contained hydrogen, methane, ammonia, and water which led to the formation of organic molecules.
• Miller and Urey simulated early Earth conditions and produced organic compounds, including amino acids.
• RNA World Hypothesis: RNA was the earliest genetic material because of its catalytic and information storage capabilities.

Evolutionary Concepts

• Mutation is the source of new alleles.
• Evolution is driven by mutation, selection, drift, and gene flow.
• Gene flow can alter fitness.
• Microevolution: Small genetic changes within a population over time.
• Macroevolution: Large-scale patterns, like speciation and extinction.