The Importance of Physiology

The Highly Integrative Nature of Physiology

Mechanism and Origin: Physiology’s Two  Central Questions

• The study of mechanism: How do modern-day animals carry out their functions?
• The study of origin: Why do modern-day animals possess the mechanisms they do?
• Natural selection is a key process of evolutionary origin
• Mechanism and adaptive significance are distinct concepts that do not imply each other

This Book’s Approach to Physiology

Animals

• The structural property of an animal that persists through time is its organization
• Most cells of an animal are exposed to the internal environment, not the external environment
• The internal environment may be permitted to change when the external environment changes, or it may be kept constant
• Homeostasis in the lives of animals: Internal constancy is often critical for proper function
• BOX 1.1 Negative Feedback
• Time in the lives of animals: Physiology changes in five time frames
• BOX 1.2 The Evolution of Phenotypic Plasticity
• Size in the lives of animals: Body size is one of an animal’s most important traits

Environments

• Earth’s major physical and chemical environments
• The environment an animal occupies is often a microenvironment or microclimate
• Animals often modify their own environments

Evolutionary Processes

• Some processes of evolution are adaptive, others are not
• A trait is not an adaptation merely because it exists
• Adaptation is studied as an empirical science
• Evolutionary potential can be high or low, depending on available genetic variation

Individual Variation and the Question of “Personalities” within a Population