iii

iii

BIOLOGY

HOW

LIFE

WORKS

SECOND EDITION

James Morris

BRANDEIS UNIVERSITY

Daniel Hartl

HARVARD UNIVERSITY

Andrew Knoll

HARVARD UNIVERSITY

Robert Lue

HARVARD UNIVERSITY

Melissa Michael

UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN

ANDREW BERRY, ANDREW BIEWENER,

BRIAN FARRELL, N. MICHELE HOLBROOK

HARVARD UNIVERSITY

iv

PUBLISHER Kate Ahr Parker

ACQUISITIONS EDITOR Beth Cole

LEAD DEVELOPMENTAL EDITOR Lisa Samols

SENIOR DEVELOPMENTAL EDITOR Susan Moran

DEVELOPMENTAL EDITOR Erica Champion

EDITORIAL ASSISTANTS Jane Taylor, Alexandra Garrett, Abigail Fagan

REVIEW COORDINATOR Donna Brodman

PROJECT MANAGER Karen Misler

DIRECTOR OF MARKET DEVELOPMENT Lindsey Jaroszewicz

EXECUTIVE MARKETING MANAGER Will Moore

ART AND MEDIA DIRECTOR Robert Lue, Harvard University

EXECUTIVE MEDIA EDITOR Amanda Nietzel

SENIOR DEVELOPMENT EDITOR FOR TEACHING & LEARNING STRATEGIES Elaine Palucki

SENIOR MEDIA PRODUCER Chris Efstratiou

PROJECT EDITOR Robert Errera

MANUSCRIPT EDITOR Nancy Brooks

DIRECTOR OF DESIGN, CONTENT MANAGEMENT Diana Blume

DESIGN Tom Carling, Carling Design Inc.

ART MANAGER Matt McAdams

ILLUSTRATIONS Imagineering

CREATIVE DIRECTOR Mark Mykytiuk, Imagineering

PHOTO EDITOR Christine Buese

PHOTO RESEARCHERS Lisa Passmore and Richard Fox

PRODUCTION MANAGER Paul Rohloff

COMPOSITION Sheridan Sellers

PRINTING AND BINDING RR Donnelley

COVER IMAGE: Thorsten Henn/Getty Images

Library of Congress Control Number: 2015950976

ISBN-13: 978-1-4641-2609-3

ISBN-10: 1-4641-2609-7

©2016, 2013 by W. H. Freeman and Company

All rights reserved.

Printed in the United States of America

Third printing

Macmillan Learning

W. H. Freeman and Company

One New York Plaza

Suite 4500

New York, NY 10004-1562

www.macmillanhighered.com