Table of Contents
Behavioral biology (also called ethology) is the branch of biology that studies what organisms do and why they do it—from simple reflexes to complex social interactions. Because behavior is often the most immediately visible aspect of life, it forms a natural bridge between physiology, ecology, evolution, and even psychology.
This introductory chapter provides the overarching framework for understanding behavior in biological terms. Later chapters will go into specific goals, methods, developmental aspects, mechanisms, and adaptive functions of behavior.
What Is Behavior in a Biological Sense?
In biology, behavior usually means:
All movements, actions, or changes in posture or activity of an organism that can be observed and that are influenced by internal states and/or external stimuli.
Key points:
- Behavior is activity of whole organisms, not just isolated cells.
- It is usually observable, at least in principle (even if we need instruments).
- It is influenced both by:
- External factors (stimuli from environment: light, sound, chemicals, other organisms).
- Internal factors (hormones, nervous system, motivations, genetic predispositions, learning history).
Examples across different organisms:
- Bacteria: swimming toward nutrients (chemotaxis).
- Plants: turning leaves toward light, closing traps in Venus flytraps.
- Invertebrates: ants following pheromone trails, spiders building webs.
- Vertebrates: bird song, courtship dances, territorial defense, parental care.
- Humans: language, social rituals, tool use, cooperative behavior.
Behavioral biology treats all these as natural phenomena that can be described, measured, compared, and explained.
Why Study Behavior Biologically?
Behavioral biology seeks to answer questions such as:
- How is a behavior produced?
(Which sensory systems, nerves, muscles, and hormones are involved?) - How does a behavior develop in an individual?
(What roles do genes, environment, learning, and experience play?) - What is the function of a behavior?
(How does it affect survival and reproduction?) - How did the behavior evolve, and how is it distributed across related species?
These four perspectives are often summarized as four complementary levels of explanation (after Niko Tinbergen):
- Mechanism (causation) – Immediate internal and external triggers.
- Ontogeny (development) – Changes from embryo to adult.
- Function (adaptive value) – Impact on fitness (survival/reproduction).
- Phylogeny (evolutionary history) – How and when the trait arose.
Behavioral biology treats none of these levels as “more real” than the others; together, they provide a complete biological understanding.
Central Concepts in Behavioral Biology
Behavior as Part of the Phenotype
Genes do not “code for behavior” in a simple, direct way. Instead, genes influence:
- Structure and function of the nervous system,
- Hormonal systems,
- Sensory organs,
- Muscles and other effectors,
which then interact with the environment to produce behavioral phenotypes. Thus:
- Behavior is part of an organism’s phenotype, just like body shape or coloration.
- It can be subject to natural and sexual selection, leading to adaptation.
This has several important consequences:
- Behavioral traits can show variation within populations.
- They can be heritable to some degree.
- They can evolve under selection pressures (e.g., predation, mate choice, social environment).
Innate and Learned Components
Most behaviors are shaped by both innate (genetically influenced) and learned (experience-dependent) components. Behavioral biology asks:
- Which aspects of a behavior appear without specific learning?
- Which aspects require individual experience or social learning?
- How flexible is a behavior? Can it be modified by changing circumstances?
Later chapters will treat innate and learned behavior separately; here it is enough to note that:
- There are no purely “genetic” behaviors that are entirely independent of environment.
- There are no purely “environmental” behaviors that occur independently of the organism’s biological makeup.
Behavior emerges from their interaction.
Behavior in an Ecological and Social Context
Behavior has meaning only in relation to:
- The organism’s environment (habitat, climate, resource distribution),
- Its social environment (group structure, competition, cooperation),
- Its life history (growth, reproduction, lifespan).
For example:
- Feeding behavior depends on where food is, how it is distributed, and who else is competing for it.
- Anti-predator behaviors (camouflage, fleeing, alarm calls) depend on which predators are present and how they hunt.
- Social behaviors (dominance, cooperation, parental care) depend on group size, relatedness, and ecological conditions.
Thus behavioral biology is closely linked to ecology and evolutionary biology.
Levels of Organization in Behavior
Behavior can be studied at different organizational levels:
- Individual level: how a single animal responds to stimuli and makes decisions.
- Dyadic or small-group level: pair bonds, dominance relationships, parent–offspring interactions.
- Group or population level: flocking, schooling, group decision-making, cultural traditions in animals.
Behavioral biology asks how individual rules of behavior can produce complex group phenomena (e.g., bird flocks, ant colonies) without any central control.
Approaches Within Behavioral Biology
Over time, different schools and emphases have developed. The following distinctions are important as a background:
Classical Ethology and Comparative Approach
Classical ethology (Konrad Lorenz, Niko Tinbergen, Karl von Frisch and others) emphasized:
- Natural environments and observation of animals in the wild.
- Describing species-typical behaviors (ethograms).
- Comparing closely related species to draw conclusions about evolution of behavior.
- Detailed analysis of fixed action patterns, sign stimuli, and motivation states.
This comparative approach treats each species’ behavior as adapted to its particular ecological niche.
Behavioral Ecology and Sociobiology
Later, behavioral ecology and sociobiology focused especially on:
- How behavior maximizes reproductive success under ecological constraints.
- Trade-offs between different components of fitness (e.g., current vs. future reproduction).
- Cost–benefit analyses, often formalized with simple optimization models.
Typical questions:
- Under what conditions is it advantageous to defend a territory?
- When should an animal invest energy in many small offspring vs. few large ones?
- When does cooperation between unrelated individuals evolve?
This perspective strongly links behavior to evolutionary game theory and population-level processes.
Neuroethology and Mechanistic Approaches
With advances in neurobiology, neuroethology developed, combining field behavior with:
- Studies of sensory processing (e.g., echolocating bats, electric fish),
- Neural circuits generating motor patterns (e.g., insect flight, bird song),
- The role of neurotransmitters and neuromodulators in motivation and learning.
Here the emphasis is on how nervous systems produce the observed behavior.
Integrative and Interdisciplinary Perspectives
Modern behavioral biology is highly integrative, overlapping with:
- Genetics and molecular biology (e.g., genes affecting courtship in fruit flies),
- Endocrinology (hormones and seasonal behaviors),
- Psychology and cognitive science (memory, decision-making, problem-solving),
- Anthropology (human social behavior, cultural variation),
- Conservation biology (behavioral needs in threatened species, human–wildlife conflicts).
This interdisciplinarity allows behavior to be studied from cells to societies.
Basic Principles Guiding Behavioral Studies
Across subfields, several general principles recur:
- Objectivity and operational definitions
Behaviors are described in terms of observable actions, not subjective impressions.
Example: Instead of “the animal is angry,” one records “ears laid back, teeth bared, vocalizing at X frequency.” - Standardized observation and recording
To compare individuals or species, behaviors must be: - Clearly defined,
- Recorded systematically (time sampling, event sampling),
- Analyzed quantitatively where possible.
- Comparative method
Different species and populations are compared to: - Identify general patterns,
- Distinguish species-specific traits,
- Infer evolutionary pathways.
- Hypothesis testing
Observations lead to hypotheses about causes or functions of behavior.
These are tested through: - Controlled experiments (where ethical and feasible),
- Natural experiments (e.g., comparing islands or habitats),
- Modeling and simulations.
- Ethical consideration
Because behavior studies involve living animals—often vertebrates—ethical handling is central: - Minimizing stress and pain,
- Justifying interventions,
- Considering welfare both in the lab and the field.
Behavior as a Link Between Biology and Human Self-Understanding
Behavioral biology is especially relevant for humans because:
- It provides comparative insight: how human behavior resembles or differs from that of other primates and animals.
- It helps to distinguish between biological predispositions and cultural influences.
- It contributes to debates about:
- Aggression and cooperation,
- Gender roles,
- Parenting and family structures,
- Communication and language,
- The concept of “free will” and decision-making.
At the same time, behavioral biology does not claim that human behavior is only biology; rather, it emphasizes that biological, psychological, and cultural levels interact.
Orientation for the Following Chapters
The subsequent chapters of this section will build on this general framework:
- Goals and Methods of Behavioral Biology will clarify what questions behavioral biologists ask in practice and how they collect and analyze behavioral data.
- Development of Behavior will focus on how behavior arises during individual life, including early experiences and juvenile behavior.
- Mechanisms of Behavior will deal with how movements are coordinated, and how innate and learned behaviors interact in the nervous and hormonal systems.
- Adaptiveness of Behavior will examine why certain behaviors increase survival and reproductive success, and how behaviors shape social systems and communication.
Together, these chapters will provide a comprehensive introduction to behavior as an essential aspect of life, firmly rooted in biological principles yet directly observable in everyday encounters with animals and humans.