Introduction to Biology and Evolution by Natural Selection

What is Life?

Defining Characteristics of Life

• All life is cellular: All living organisms are composed of one or more cells, which are the basic units of structure and function in living things.

• Life reproduces: Living organisms reproduce, either sexually or asexually. Cells divide to produce new cells, and there is no spontaneous generation of life from non-living matter.

• Hereditary information is stored in genes: Genetic information is encoded in DNA and passed from one generation to the next.

• Organisms acquire and use energy: All living things require energy to maintain order, grow, and reproduce. This energy is obtained through metabolic processes such as photosynthesis and cellular respiration.

• Organisms evolve: Populations of organisms change over time through the process of evolution, driven by mechanisms such as natural selection.

Biology Across Scales

Levels of Biological Organization

• Molecules → Organelles → Cells → Tissues → Organs → Organ systems → Organisms → Populations → Communities → Ecosystems → Biosphere

• Biology studies life at all these scales, from the molecular to the global.

Biological Taxonomy

Hierarchical Classification of Life

• Each level is called a taxon (plural: taxa), which is a group of one or more populations of organisms.

Level	Description
Domain	Broadest category; e.g., Bacteria, Archaea, Eukarya
Kingdom	Second broadest; e.g., Animalia, Plantae, Fungi
Phylum	Groups of related classes
Class	Groups of related orders
Order	Groups of related families
Family	Groups of related genera
Genus	Groups of related species
Species	Basic unit of classification; a group of interbreeding organisms

Unit 1: Evolution

Introduction to Evolution

• Evolution is the central unifying concept in biology, explaining the diversity and unity of life.

• Fossil evidence, comparative anatomy, and genetic data all support the theory of evolution.

Evolution by Natural Selection

Historical Context and Key Figures

• Charles Darwin and Russell Wallace independently developed the theory of evolution by natural selection.

• Darwin published "On the Origin of Species" in 1859.

• This theory was radically different from the idea of special creation, which held that species are independent, life is young, and species are immutable.

Principles of Natural Selection

• Change in species through time is based on variation among individuals in populations.

• Individuals with certain traits produce more offspring than others without these traits.

• This process is called natural selection.

• Descent with modification: Over generations, populations accumulate changes, leading to the diversity of life.

Predictions of Darwin's Descent with Modification

• Species change through time: Fossil evidence shows gradual changes in species (e.g., evolution of horses).

• Species are related by common ancestry: Phylogenetic trees and comparative anatomy support this idea.

Evidence for Descent with Modification

1. Geologic Time is Vast

• Geologic history can be traced through sedimentary layers and radiometric dating.

2. Fossil Record

• Fossils provide evidence of extinct species and show that species are dynamic and change over time.

• More than 99% of all species that have ever lived are now extinct.

3. Transitional Features

• Traits in fossils that are intermediate between ancestral and derived species are called transitional features.

• Extant species in an area often resemble extinct species from the same region ("law of succession").

• Darwin proposed that these similarities indicate relatedness.

What is a Scientific Theory?

Definition and Components

• A scientific theory is not a guess.

• It explains a broad class of observations and is widely supported by evidence.

• Usually consists of:

  • Pattern component: Describes how things are in nature based on observations.

  • Process component: Explains the mechanism by which that pattern is produced.

Learning Objectives

• Define adaptation, fitness, evolution, and theory, and explain their scientific meanings.

• Explain how the fossil record and genetic/structural homologies provide evidence for evolution.

• Describe the connection between mutation, heritable variation, and changes in allele frequencies due to selection.

• Use examples to explain why evolution by natural selection is not random or progressive, and why adaptations are not "perfect".

Additional info: These notes are based on introductory slides and lecture content for a General Biology course, focusing on the nature of life, biological organization, taxonomy, and the foundational principles of evolution by natural selection.