General Biology: Study Guide on Evolution, Speciation, and Mechanisms of Change - Exam 1

Introduction to Scientific Inquiry and Evolution

Hypotheses, Theories, and Characteristics of Science

Scientific inquiry relies on the formulation of hypotheses and theories to explain natural phenomena. Understanding the distinction between these concepts is foundational in biology.

• Hypothesis: A testable guess or prediction that can be investigated through experimentation.

• Scientific Theory: A well-supported explanation that is widely accepted by the scientific community.

• Characteristics of Science:

  • Based on evidence

  • Testable and falsifiable

  • Repeatable

  • Predictable

Foundations of Evolutionary Theory

Contributors to Evolutionary Thought

Several scientists contributed to the development of evolutionary theory, including those who proposed mechanisms for how species change over time.

• Alfred Russel Wallace: Independently conceived the concept of natural selection alongside Darwin.

• Jean-Baptiste Lamarck: Proposed that organisms change over time through the inheritance of acquired characteristics.

• Charles Lyell: Suggested that Earth's geological features change gradually over long periods, influencing Darwin's ideas.

• Thomas Malthus: Argued that populations grow faster than resources, leading to competition and influencing Darwin's theory of natural selection.

Mechanisms of Evolutionary Change

Evolutionary change occurs through several mechanisms that alter allele frequencies in populations over time.

• Natural Selection: Differential survival and reproduction of individuals due to differences in phenotype.

• Mutation: Random changes in DNA that introduce new genetic variation.

• Migration (Gene Flow): Movement of alleles between populations.

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

• Non-random Mating: Mating that is not random with respect to genotype or phenotype.

Speciation and Reproductive Isolation

Types of Speciation

Speciation is the process by which new species arise, often through reproductive isolation.

• Allopatric Speciation: Occurs when populations are separated by a physical barrier (e.g., river, mountain) and evolve into distinct species.

• Sympatric Speciation: Occurs when populations diverge within the same geographic area, often due to genetic, behavioral, or ecological differences.

Reproductive Isolation Mechanisms

Reproductive isolation prevents gene flow between populations, leading to speciation.

• Prezygotic Mechanisms: Prevent mating or fertilization between species (e.g., behavioral, temporal, mechanical isolation).

• Postzygotic Mechanisms: Occur after fertilization, resulting in non-viable or sterile offspring (e.g., mule sterility).

Isolation Type	Example
Prezygotic	Different mating calls in frogs
Postzygotic	Mule (horse x donkey) is sterile

Sexual Dimorphism and Evolutionary Explanations

Definition and Examples

Sexual dimorphism refers to differences in appearance between males and females of the same species, often driven by sexual selection.

• Sexual Selection: Traits that increase reproductive success are favored, such as bright plumage in male birds or large antlers in male deer.

• Examples:

  • Peacock males have bright tails to attract females.

  • Deer males have antlers; females do not.

Genetics and Population Evolution

Key Genetic Terms

Understanding basic genetic terminology is essential for studying population genetics and evolutionary change.

• Allele: A variant of a gene at a specific locus on a chromosome.

• Genotype: The genetic makeup of an organism.

• Phenotype: The observable traits of an organism.

• Homozygous: Having two identical alleles for a gene.

• Heterozygous: Having two different alleles for a gene.

Example of allele combinations:

• AA (homozygous dominant)

• aa (homozygous recessive)

• Aa (heterozygous)

Hardy-Weinberg Equilibrium

The Hardy-Weinberg principle describes the genetic makeup of a population that is not evolving.

• Conditions for equilibrium:

  1. No natural selection

  2. No mutation

  3. No migration (gene flow)

  4. Large population size (no genetic drift)

  5. Random mating

Equation:

• $p^2 + 2pq + q^2 = 1$

• $p + q = 1$

Evidence for Evolution

Types of Evidence

Multiple lines of evidence support the theory of evolution.

• Fossil Record: Shows transitional forms and changes over time.

• Comparative Anatomy: Homologous structures indicate common ancestry.

• Developmental Biology: Similar embryological stages among related species.

• Biogeography: Distribution of species supports evolutionary relationships.

• Contemporary Evidence: Examples include antibiotic resistance in bacteria.

Natural Selection and Population Adaptation

Conditions for Natural Selection

Natural selection acts on populations when certain conditions are met.

• The population is variable

• Variation is heritable

• Some variants survive and reproduce better than others

These conditions lead to adaptation and evolutionary change over time.

Interpreting Evolutionary Graphs

Variation, Heritability, and Selection

Graphs can illustrate how selection acts on traits within populations, showing changes in trait distributions over time.

• Directional selection shifts the mean trait value.

• Stabilizing selection reduces variation around the mean.

• Disruptive selection favors extreme trait values.

Example: Graphs showing changes in beak size in finch populations due to environmental pressures.