Description
Homology—a similar trait shared by different species and derived from common ancestry, such as a seal’s fin and a bird’s wing—is one of the most fundamental yet challenging concepts in evolutionary biology. This groundbreaking book provides the first mechanistically based theory of what homology is and how it arises in evolution.
Günter Wagner, one of the preeminent researchers in the field, argues that homology, or character identity, can be explained through the historical continuity of character identity networks—that is, the gene regulatory networks that enable differential gene expression. He shows how character identity is independent of the form and function of the character itself because the same network can activate different effector genes and thus control the development of different shapes, sizes, and qualities of the character. Demonstrating how this theoretical model can provide a foundation for understanding the evolutionary origin of novel characters, Wagner applies it to the origin and evolution of specific systems, such as cell types; skin, hair, and feathers; limbs and digits; and flowers.
The first major synthesis of homology to be published in decades, Homology, Genes, and Evolutionary Innovation reveals how a mechanistically based theory can serve as a unifying concept for any branch of science concerned with the structure and development of organisms, and how it can help explain major transition
Chapter
Variational Modalities: More Than One Way of Being a Certain Character
Character Identity and Repeated Body Parts: Serial Homology
Character Swarms: Persistent Cases of Partial Individuality
Alternative Conceptualizations of Homology
A Case for Conceptual Liberalism
Sorting Patterns of Morphological Variation
Chapter 3 A Genetic Theory of Homology
Why Continuity of Genetic Information Is Not Enough
Lessons from the Variable Development of Homologs
Homeotic Genes and Character Identity
A Model: Character Identity Networks
Variation and Conservation of Segment Development
Eye Development and the ey/so/eya/dac (ESED) Networks
The Role of Protein-Protein Interactions
Characteristics of Character Identity Networks
Chapter 4 Evolutionary Novelties: The Origin of Homologs
Revisiting the Conceptual Roadmap: Which Way to Novelty?
Phenomenological Modes for the Origin of Type I Novelties
From Phenomenology to Explanation
Explaining Robustness and Canalization
Natural Selection and the Origin of Novelties: A Roundup
Chapter 5 Developmental Mechanisms for Evolutionary Novelties
The Environment’s Role in Evolutionary Innovations
Where Does the Positional Information for Novel Characters Come From?
Derived Mechanical Stimuli and the Origin of Novelties in the Avian Hind Limb Skeleton
The Origin of Character Identity Networks
The Evolution of Novel Signaling Centers
The Developmental Biology of Novelties: Reflections
Chapter 6 The Genetics of Evolutionary Novelties
Evolution of cis-Regulatory Elements
Are Novel Pigment Spots Novelties, and Why Does It Matter?
Sex Combs: The Origin of a ChIN
Origin of Novel cis-Regulatory Elements: Transposable Elements
The Role of Gene Duplications
Evolution of Transcription Factor Proteins
A Material Difference between Innovation and Adaptation?
Chapter 7 The Long Shadow of Metaphysics on Research Programs
Metaphysics as the Sister of Science
Individuals and Natural Kinds
Part II : Paradigms and Research Programs
Chapter 8 Cell Types and Their Origins
Developmental Genetics of Cell Types
The Evolutionary Origin of Cell Types
Case Studies of Cell Typogenesis
Chapter 9 Skin and a Few of Its Derivatives
Developmental Evolution of Amniote Skin and Skin Appendages
Mammalian Skin Derivatives: Hairs and Breasts
Devo-Evo of Bird Skin: Scales into Feathers
Chapter 10 Fins and Limbs
Concluding Reflection on the Nature of Character Identity
Chapter 11 Digits and Digit Identity
Digits Come and Go: Is There a Pentadactyl Ground Plan?
Developmental and Morphological Heterogeneity of the Tetrapod Hand
Digit Loss and Re-evolution in Amniotes
The Pentadactyl Autopodium (PDA) Type
Developmental Genetics of Digit Identity
Digit Identity: Real or Imaginary?
A Fingerpost on the Nature of Character Identity
Angiosperm Phylogeny and Flower Character Evolution
Genetics of Canonical Flower Development
The Developmental Genetic Architecture of the Flower Bauplan
Flower Variation and Novel Flower Organ Identities
The Origin of the Bisexual Flower Developmental Type
Perianth Evolution and the Origin of Petals
Genetics of Organ Identity: Challenges from Gene Duplication
Chapter 13 Lessons and Challenges
What Are the Core Claims of This Model of Homology?
Characters Are Real But Historically Limited
Homology Is Not Hierarchical
The Quasi-Cartesian Model of Character Identity
Character Individuality and Gene Regulatory Network Cooperativity
Open Questions and Difficulties
Population, Tree, and Homology Thinking
Homology, Genes, and Evolutionary Innovation
：Homology, Genes, and Evolutionary Innovation
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