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PUBLISHER: Katherine Parker

SENIOR ACQUISITIONS EDITOR: Bill Minick

SENIOR DEVELOPMENTAL EDITORS: Andrea Gawrylewski and Beth Marsh

MARKETING MANAGER: Maureen Rachford

SENIOR MEDIA AND SUPPLEMENTS EDITOR: Amy Thorne

SENIOR MEDIA PRODUCER: Chris Efstratiou

MEDIA PRODUCER: Jenny Chiu

EDITORIAL ASSISTANTS: Shannon Moloney and Allison Greco

DIRECTOR OF DESIGN, CONTENT MANAGEMENT: Diana Blume

COVER AND TEXT DESIGN: Dirk Kaufman

SENIOR PROJECT EDITOR: Vivien Weiss

PRODUCTION MANAGER: Susan Wein

ILLUSTRATIONS COORDINATOR: Janice Donnola

ILLUSTRATIONS: Tommy Moorman

PHOTO EDITORS: Robin Fadool and Jennifer Atkins

PHOTO RESEARCHERS: Elyse Rieder, Jennifer Atkins, and Stephanie Heimann-Roland

ART MANAGER: Matthew McAdams

COMPOSITION: Sheridan Sellers

PRINTING AND BINDING: RR Donnelley

COVER AND TITLE PAGE: Jim Richardson/National Geographic Creative

Library of Congress Control Number: 2015953764

ISBN-13: 978-0-7167-6187-7

ISBN-10: 0-7167-6187-4

© 2016 by W. H. Freeman and Company

All rights reserved

Printed in the United States of America

First printing

W. H. Freeman and Company

One New York Plaza

Suite 4500

New York, NY 10004-1562

SUSTAINABILITY PLEDGE Macmillan is committed to lessening our company’s impact on the environment. The Macmillan family of publishing houses intends to reduce our 2020 CO₂ emissions by 64% against a 2009 baseline.

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To all people everywhere, and the web of life that sustains us