Basic Principles of Animal Form and Function
Overview: Diverse Forms, Common Challenges
Animals inhabit almost every part of the biosphere.
Despite their great diversity, all animals must solve a common set of problems.
All animals must obtain oxygen, nourish themselves, excrete wastes, and move.
Animals of diverse evolutionary histories and varying complexity must solve
these general challenges of life.
Consider the long, tongue-like proboscis of a hawk moth, a structural adaptation
Recoiled when not in use, the proboscis extends as a straw through which the
moth can suck nectar from deep within tube-shaped flowers.
Analyzing the hawk moth’s proboscis gives clues about what it does and how it
is the study of the structure of an organism.
is the study of the functions an organism performs.
Natural selection can fit structure to function by selecting, over many
generations, the best of the available variations in a population.
Searching for food, generating body heat and regulating internal temperature,
sensing and responding to environmental stimuli, and all other animal activities
require fuel in the form of chemical energy.
The concept of bioenergetics—how organisms obtain, process, and use energy
resources—is a connecting theme in the comparative study of animals.
Concept 40.1 Physical laws and the environment constrain
animal size and shape
An animal’s size and shape, features often called “body plans” or “designs,” are
fundamental aspects of form and function that significantly affect the way an
animal interacts with its environment.
The terms plan and design do not mean that animal body forms are products of
The body plan or design of an animal results from a pattern of development
programmed by the genome, itself the product of millions of years of evolution
due to natural selection.
Physical requirements constrain what natural selection can “invent.”
An animal such as the mythical winged dragon cannot exist. No animal as large
as a dragon could generate enough lift to take off and fly.
Similarly, the laws of hydrodynamics constrain the shapes that are possible for
aquatic organisms that swim very fast.
Tunas, sharks, penguins, dolphins, seals, and whales are all fast swimmers.
All have the same basic fusiform shape, tapered at both ends.