Evolution and Natural Selection: Study Guide

Vocabulary and Key Concepts

Essential Terms in Evolutionary Biology

• Taxonomy: The science of naming and classifying organisms.

• Binomial nomenclature: A two-part scientific naming system for species, consisting of the Genus (capitalized) and species (lowercase), e.g., Homo sapiens.

• Evolution: Change in the genetic composition of a population over time.

• Natural selection: The process by which individuals with advantageous traits survive and reproduce more successfully.

• Fossil: Preserved remains or traces of ancient organisms.

• Gene pool: The total collection of genes in a population at any one time.

• Genetic drift: Random changes in allele frequencies, especially in small populations.

• Gene flow: The movement of alleles between populations due to migration.

• Homologous structures: Anatomical features with similar structure but different functions, indicating common ancestry.

• Vestigial structures: Structures that have lost their original function through evolution.

• Mutation: A change in the DNA sequence, introducing new genetic variation.

Taxonomy & Binomial Names

Classification and Naming of Organisms

• Binomial nomenclature provides a universal naming system for all species.

• Each species is given a two-part name: Genus (capitalized) and species (lowercase).

• Example: Homo sapiens

Taxonomic Levels (Know Both Orders)

• Largest to Smallest: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

• Smallest to Largest: Species → Genus → Family → Order → Class → Phylum → Kingdom → Domain

Background Leading to Darwin

Historical Context for Evolutionary Theory

• Fossil evidence showed that species change over time.

• Geological discoveries indicated that Earth is very old.

• Malthus observed that populations grow faster than food supply, leading to competition.

• Artificial selection (selective breeding) demonstrated that humans can cause changes in species; nature can do the same.

Darwin's History (Quick Version)

Key Events in Darwin's Scientific Journey

• Darwin sailed for 5 years on the HMS Beagle.

• He made observations in South America and the Galápagos Islands.

• He developed his ideas about natural selection and evolution.

• Darwin published On the Origin of Species in 1859.

Darwin's Primary Hypotheses

Core Principles of Evolution by Natural Selection

• Descent with modification: Species change over time and share common ancestors.

• Natural selection: Nature favors traits that enhance survival and reproduction.

Descent With Modification

How Species Change Over Time

• All living things descend from older species.

• Over generations, populations accumulate changes, leading to diversity.

Natural Selection (3 Key Ideas)

Mechanism of Evolution

1. Variation exists in a population.

2. Overproduction: More offspring are produced than can survive.

3. Differential survival and reproduction: Individuals with better traits survive and reproduce more successfully.

Evolutionary Theory (Publications)

Development and Communication of Evolutionary Ideas

• Darwin and Wallace independently proposed the idea of natural selection.

• Darwin's Origin of Species (1859) explained natural selection as the mechanism of evolution.

Evidence for Evolution

Fossil Types and Their Importance

• Fossil types: Imprints, casts, molds, bones/shell parts, amber fossils.

• Fossil record importance:

  • Shows changes in species over time.

  • Shows extinction and appearance of new species.

  • Provides a timeline of life on Earth.

More Evidence for Evolution

• Homologous structures: Similar structure, different function → shared ancestry.

• Molecular biology: DNA and protein similarities show evolutionary relationships.

• Vestigial structures: Small or unused body parts left from ancestors (e.g., human appendix).

Main Sources of Genetic Variation

How Populations Gain New Traits

1. Mutations: Random changes in DNA.

2. Independent assortment: Random distribution of chromosomes during meiosis.

3. Random fertilization: Any sperm can fertilize any egg, increasing variation.

Ways Evolution Changes a Gene Pool

Mechanisms of Evolutionary Change

1. Natural selection: Adaptive changes in allele frequencies.

2. Genetic drift: Random changes, especially in small populations.

3. Gene flow: Movement of alleles between populations.

Genetic Drift Effects

Special Cases of Genetic Drift

• Bottleneck effect: A sudden reduction in population size leads to a small surviving group with reduced genetic variation.

• Founder effect: A small group starts a new population, resulting in little genetic variation compared to the original population.

Summary Table: Mechanisms of Evolution

Mechanism	Description	Effect on Gene Pool
Natural Selection	Favors traits that increase survival and reproduction	Adaptive change; increases frequency of beneficial alleles
Genetic Drift	Random changes in allele frequencies, especially in small populations	Can decrease genetic variation; may fix or eliminate alleles
Gene Flow	Movement of alleles between populations	Increases genetic variation within populations; reduces differences between populations

Key Equations

• Hardy-Weinberg Equation (for genetic equilibrium):

$p^2 + 2pq + q^2 = 1$

Where:

• $p$ = frequency of dominant allele

• $q$ = frequency of recessive allele

• $p^2$ = frequency of homozygous dominant genotype

• $2pq$ = frequency of heterozygous genotype

• $q^2$ = frequency of homozygous recessive genotype

Additional info: The Hardy-Weinberg equation is used to predict genotype frequencies in a non-evolving population and serves as a null hypothesis for detecting evolutionary change.