Carolyn Fry - Seeds: A Natural History

CAROLYN FRY

SEEDS

A NATURAL HISTORY

THE UNIVERSITY OF CHICAGO PRESS
Chicago

For my mother and father, Jane and Roger Fry

Carolyn Fry is an author and journalist specializing in science, conservation, natural history, and adventure travel. She has written six books on these subjects, including The Plant Hunters, also published by The University of Chicago Press.

Carolyn Fry asserts her moral right to be recognized as the author of this work.

The views expressed in this work are those of the author and do not necessarily reflect those of the publisher or the Royal Botanic Gardens, Kew.

The University of Chicago Press, Chicago 60637
2016 The Ivy Press Limited

All rights reserved. Published 2016.

ISBN-13: 978-0-226-22435-0 (cloth)
ISBN-13: 978-0-226-22449-7 (e-book)

DOI: 10.7208/chicago/9780226224497.001.0001

Library of Congress Cataloging-in-Publication Data

Names: Fry, Carolyn (Science writer), author.
Title: Seeds : a natural history / Carolyn Fry.
Description: Chicago : The University of Chicago Press, 2016.
| Includes bibliography and index.
Identifiers: LCCN 2015034444| ISBN 9780226224350 (cloth : alk. paper) | ISBN 9780226224497 (e-book)
Subjects: LCSH: SeedsPopular works. | BotanyPopular works. | Natural historyPopular works.
Classification: LCC QK661 .F79 2016 | DDC 581.4/67dc23 LC record available at http://lccn.loc.gov/2015034444

This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).

This book was conceived, designed, and produced by

Ivy Press

210 High Street, Lewes

East Sussex BN7 2NS

United Kingdom

www.ivypress.co.uk

PUBLISHER Susan Kelly

CREATIVE DIRECTOR Michael Whitehead

EDITORIAL DIRECTOR Tom Kitch

ART DIRECTOR Wayne Blades

COMMISSIONING EDITOR Jacqui Sayers

PROJECT EDITOR Joanna Bentley

BOOK DESIGN Evelin Kasikov

ILLUSTRATOR Emma Kelly

PICTURE RESEARCHER Katie Greenwood

Front cover: Light micrograph of strawberry seeds. Science Photo Library/Eye of Science.

CONTENTS

SEED BANKS AROUND THE WORLD

INTRODUCTION

A s this book sets out to demonstrate, we have much to thank seeds for. Not only do they provide half the calories consumed by humanity today, but they also helped humans to evolve and civilization to develop. Some 3.5 million years ago, seeds provided a calorific boost to early hominids, who moved out of the trees and on to Africas savannas; switching from eating leaves and fruit to consuming the seeds of grasses and sedges helped them develop bigger brains and gave them an evolutionary advantage over other primates. It was these early hominids, our ancient ancestors, who gave rise to the human race.

Later, the seeds of annuals, such as maize, wheat, and rice, helped to underpin the rise of civilization. Because they have a yearly lifecycle, annuals can be cultivated relatively easily. Once early humans discovered they could take control of their food supply by farming plants, they were able to swap a nomadic lifestyle for a more settled existence in ever-larger communities. In the majority of cases, human societies grew up on seed-based diets, although roots and tubers were also important. Not having to spend their entire time foraging enabled these early citizens to do other things. They began bearing more children, organizing their communities in a structured way, and studying the world around them.

The story of seeds begins long before humans came on the scene, however. To understand where seeds and plants come from requires us to go back 450 million years, some 220 million years before the dinosaurs evolved. At this time, ocean-dwelling algae that had evolved over time from single-celled microbes began inhabiting pools of freshwater on land. Slowly, a process of natural selection began, whereby individuals that could tolerate the surrounding environmental conditions survived, and those that could not fell by the wayside. Over many millions of years, as plants competed with each other for space, sunlight, water, and nutrients, a complex series of evolutionary changes led to the great diversity of land plants we see on Earth today.

The evolution of the seed proved to be particularly beneficial for plants. Before seeds, plants reproduced by spores, a process requiring water. Initially, plants produced spores of one size in their sporangia but later they evolved to produce large spores that became female reproductive organs and small spores that became male reproductive organs. Eventually, the female parts of sporangia went from producing many spores to creating just one, and retaining this spore on the plant instead of dispersing it. This became the seed, while male spores became pollen. Not requiring water to reproduce meant seed-bearing plants could tolerate drier conditions, a great advantage as climatic conditions changed.

A new plant emerges from a seed at New York's Greenbelt Native Plant Center, one of the many seed banks that are helping to preserve biodiversity.

Today, two types of seed-bearing plants exist. Gymnosperms, which include conifers, number around 1,000 species, while angiosperms, the flowering plants, number 350,000 species. The angiosperms diversified very rapidly after evolving around 100 million years ago, a process described by naturalist Charles Darwin in 1879 as an abominable mystery. He had considered that evolution only took place via natural selection in small, gradual steps. Scientists are still uncertain exactly what caused such a rapid diversification, but it is likely to involve flowering plants innovative method of sexual reproduction, their relationships with animal pollinators, and the existence of a wide variety of climatic conditions throughout their evolution.

What is certain is that the evolution of angiosperms provided plentiful plants that enabled humans to thrive. All the major root crops and vegetables we eat are angiosperms, although we rely on less than ten crops to provide 75 percent of human energy needs. These are: rice, maize, wheat, sorghum, millet, potatoes, sweet potatoes, soybean and sugar from cane and beet. Seeds are our primary source of calories and protein, with those from cereals being the most important.

Seeds from wild plants are much like people; they each have a unique genetic profile. Over the thousands of years that humans have cultivated plants for food, they have selectively bred out traits that were not helpful for farming and bred in traits that were favorable. In generally stable climates, such as those experienced by farmers until recently, the ability to survive weather conditions outside the normal range was not that important. While traits such as retaining seeds on the plant for longer, resisting disease, and providing an attractive color and pleasant flavor were desirable. This essentially meant that farmers retained genes that gave favorable results and discarded those that did not. In doing so, they developed landraces that were highly suited to local conditions.

As farming grew in scale, and techniques for creating new cultivars became more complex, the genetic diversity within many crop plants was whittled down to the bare minimum required to give high yielding, good tasting, evenly ripening crops. Growing crops with the same or similar genetic profile meant farmers knew exactly what they were going to reap, but it left the crops vulnerable to disease and climatic changes. In the mid-19th century, Irish farmers learned the hard way about the downside of farming crops with no genetic diversity, when a water mould killed the nations entire potato crop. And farmers today are learning of the importance of genetic diversity in growing crops that are resilient to climate change.