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Honors Biology
Table of Contents
Unit 11 Overview: Evolution
11.1 Darwin's Theory and Natural Selection
11.2 Evidence for Evolution
11.3 Population Genetics and Hardy-Weinberg Equilibrium
11.4 Speciation and Macroevolution

Evolution leaves traces in living organisms and the fossil record. Scientists use anatomical, fossil, biogeographical, and molecular evidence to support the theory of evolution. These clues reveal common ancestry and evolutionary relationships between species.

Comparative anatomy, vestigial structures, and embryology provide anatomical evidence. Fossils and biogeography offer insights into species' history and distribution. Molecular biology and antibiotic resistance demonstrate evolution at the genetic level, showing how species change over time.

Anatomical Evidence

Comparative Anatomy and Homologous Structures

  • Comparative anatomy studies the similarities and differences in the structures of different species
  • Helps determine evolutionary relationships between organisms
  • Homologous structures are anatomical features shared by related species
    • Derived from a common ancestor
    • Have the same basic structure and embryonic origin
    • May have different functions (penguin flipper, bat wing, human arm)
  • Analogous structures are anatomical features that have similar functions but different evolutionary origins (bird wing, insect wing)

Vestigial Structures and Embryology

  • Vestigial structures are anatomical features that have lost much or all of their original function
    • Remnants of functional structures in ancestral species
    • Indicate common ancestry (human appendix, whale pelvis, snake hind limbs)
  • Embryology studies the development of an organism from fertilization to birth
  • Embryos of different vertebrate species show similar developmental stages and structures
    • Indicates common ancestry and evolutionary relationships
    • Examples include pharyngeal pouches, tail, and notochord in human, chicken, and fish embryos

Fossil and Biogeographical Evidence

Fossil Record

  • Fossils are the preserved remains or traces of once-living organisms
  • Provide direct evidence of evolutionary changes over time
  • Transitional fossils show intermediate forms between ancestral and descendant species (Archaeopteryx, Tiktaalik)
  • Fossil record reveals the order in which species appeared and went extinct
    • Older rock layers contain fossils of more ancient species
    • Younger rock layers contain fossils of more recent species

Biogeography

  • Biogeography studies the geographic distribution of species and ecosystems
  • Explains how species are distributed across continents and islands
  • Similar environments in different parts of the world are inhabited by different but related species (marsupials in Australia, placental mammals in Europe)
  • Unique species on isolated islands evolved from ancestral species that colonized the islands (Galápagos finches, Hawaiian honeycreepers)

Molecular Evidence

Molecular Biology and DNA Sequencing

  • Molecular biology studies the structure, function, and evolution of biological molecules (DNA, RNA, proteins)
  • DNA sequencing determines the order of nucleotide bases in an organism's genome
  • Comparing DNA sequences reveals evolutionary relationships between species
    • More closely related species have more similar DNA sequences
    • Mutations accumulate over time, leading to greater differences between distantly related species
  • Molecular clocks estimate the time since two species diverged from a common ancestor based on the number of genetic differences between them

Antibiotic Resistance

  • Antibiotic resistance is the ability of bacteria to survive and reproduce in the presence of antibiotics
  • Arises through natural selection acting on genetic variation in bacterial populations
  • Bacteria with mutations that confer resistance to antibiotics survive and pass on their genes to offspring
  • Overuse of antibiotics accelerates the evolution of antibiotic-resistant bacteria (MRSA, multidrug-resistant tuberculosis)
  • Demonstrates evolution by natural selection in real-time

Key Terms to Review (16)

Common ancestry: Common ancestry refers to the concept that different species share a common ancestor from which they have evolved over time. This idea is fundamental to the theory of evolution, as it explains the similarities and differences among organisms and how they adapt to their environments through evolutionary processes.
Antibiotic resistance: Antibiotic resistance occurs when bacteria evolve and develop the ability to survive exposure to antibiotics that once effectively killed them or inhibited their growth. This phenomenon is a significant concern in medicine, as it can lead to treatment failures, prolonged illness, and increased healthcare costs. Understanding antibiotic resistance sheds light on evolutionary processes and the interactions within microbial communities, particularly in the context of the human microbiome.
Molecular clocks: Molecular clocks are tools used in evolutionary biology to estimate the time of divergence between species based on genetic mutations. They rely on the principle that mutations occur at a relatively constant rate over time, allowing scientists to calculate how long it has been since two species shared a common ancestor. This concept plays a crucial role in providing evidence for evolutionary relationships and the timeline of species evolution.
Mutations: Mutations are permanent alterations in the DNA sequence of an organism's genome. These changes can occur due to various factors, including errors during DNA replication, exposure to radiation, or chemical agents. Mutations are fundamental to the process of evolution, as they introduce genetic diversity, which can lead to new traits and adaptations in populations over time.
Transitional fossils: Transitional fossils are remains of organisms that show intermediate traits between two distinct groups, providing evidence for the evolutionary process. These fossils illustrate the gradual changes that occur over time, linking ancient species to their modern descendants and highlighting the concept of common ancestry. They are crucial in understanding how species evolve and adapt through natural selection.
Molecular biology: Molecular biology is the branch of science that focuses on the structure and function of biological macromolecules, particularly nucleic acids and proteins, and how they interact in the context of cellular processes. This field is crucial for understanding the molecular mechanisms of evolution, as it provides insights into genetic variation and the molecular basis of traits that can be acted upon by natural selection. By examining the molecular components of life, scientists can uncover how evolution shapes organisms at a fundamental level.
Embryology: Embryology is the branch of biology that studies the development of embryos from fertilization to the fetal stage. This field reveals crucial insights into how organisms develop, showcasing similarities and differences across species, which can provide evidence for evolutionary relationships. By examining embryonic development, scientists can trace how various forms of life are connected through common ancestry and highlight evolutionary adaptations.
Comparative anatomy: Comparative anatomy is the study of the similarities and differences in the anatomy of different species. This field provides crucial evidence for evolution by showcasing how different organisms may share common structures, indicating a shared ancestry, while also adapting those structures for different functions based on their environments and lifestyles.
Vestigial structures: Vestigial structures are anatomical features or behaviors that no longer serve their original purpose in a species' evolutionary history. These remnants provide evidence for evolution by demonstrating how certain traits have changed over time as organisms adapt to new environments or ways of life. They can highlight the shared ancestry among species, revealing how evolution shapes both functional and non-functional traits.
Analogous structures: Analogous structures are body parts in different species that serve similar functions but have evolved independently, without a common ancestor. These similarities arise due to convergent evolution, where organisms adapt to similar environmental challenges in similar ways, resulting in comparable adaptations even if their underlying structures differ significantly.
Homologous structures: Homologous structures are anatomical features in different species that share a common ancestry, even though they may serve different functions. These structures provide evidence for evolution, showcasing how species can diverge from a common ancestor while adapting to various environments. The similarities in their underlying anatomy highlight the concept of descent with modification.
Biogeography: Biogeography is the study of the distribution of species and ecosystems across geographic space and through geological time. It explores how environmental factors and historical events shape the patterns of biodiversity we see today. This field helps us understand how species adapt to their environments and how isolation or connectivity between regions can influence evolutionary processes.
Fossil record: The fossil record is the collection of all known fossils and their placement in the geological time scale, which provides evidence for the history of life on Earth. It serves as a crucial tool in understanding how species have changed over time and how they relate to one another, contributing to the framework of evolutionary biology and the mechanisms of natural selection.
Natural selection: Natural selection is the process by which organisms that are better adapted to their environment tend to survive and produce more offspring. This mechanism drives evolution by favoring traits that enhance survival and reproduction, leading to gradual changes in species over generations. It connects to understanding variations in populations, the evidence supporting evolutionary theory, genetic principles, and the emergence of new species.
Dna sequencing: DNA sequencing is the process of determining the precise order of nucleotides within a DNA molecule. This technique provides valuable insights into genetic information, allowing scientists to study genes, genetic variations, and evolutionary relationships among different organisms.
Genetic variation: Genetic variation refers to the differences in DNA sequences among individuals within a population. This variation is crucial for the process of evolution as it provides the raw material for natural selection, enabling populations to adapt to changing environments and contribute to the diversity of life.