From the Deep, New Light on Ancient Lives
GEOGRAPHERS have found a rudimentaryhistory of pre-Columbian societieswritten in the sediment on the bottomsof Costa Rican lakes. The researchmay have debunked a popular conceptionabout prehistoric people and the myth ofpristine forests unadulterated by humanmeddling.Sally Horn, a U.S. geographer with theUniversity of Tennessee, has worked withU.S. colleagues, students and a network ofCosta Rican scientists to understand thehistorical record preserved in the sedimentsof lakebeds and swamps at sites inthe southern Caribbean and Pacificregions, and around Chirripó, Costa Rica’shighest peak, for more than a decade.She takes core samples of up to nearlysix meters, pounding aluminum coringtubes into the lakebeds from anchored platformsset up in each lake.Pollen from crops of maize (corn), astaple cereal favored by prehistoric farmers,and charcoal, which is evidence offires, are trapped in the sediment at variousdepths, providing a record of human activity.THIS year, Horn took samples at sitesin the Caribbean lowlands and highlands,and returned to the highlands in May toinvestigate a possible site on TurrialbaVolcano.“By studying pollen grains at differentdepths in the sediment, we can reconstructhow vegetation may have changed overtime in the lake watershed,” Horn told TheTico Times. “If indigenous people cutdown the forest to grow corn and othercrops, we’ll see evidence of that in thetypes of pollen that are deposited.”Because of the way sediment settlesand layers on lakebeds as opposed to dryland, it preserves good historical records,Horn said.The research, which has yielded evidencethat prehistoric farmers burnedforests and fields, challenges the idea of“noble savages,” prehistoric indigenouspeople who lived in harmony with theirnatural surroundings.“The standard idea is that agriculturewas slash and burn,” Horn said. “We knowthat fire was associated with agriculturalactivity during many time periods.”The researchers also found evidence ofmaize crops with little evidence of burning,leading them to believe that whileslash and burn methods may have beenused to clear a forest initially, farmers onlyoccasionally burned their fields to preparethem for the next planting.“At some sites, perhaps cropping wasmore continuous – or if new sites werecleared periodically, they were not necessarilyburned. It’s something we wouldlike to understand better,” Horn said.THE evidence also contradicts theconcept of a pristine, wild forest unalteredby human activity. In an article publishedin a 2001 edition of Biotropica, the quarterlyjournal of the Association forTropical Biology and Conservation, Hornwrote that prehistoric human disturbance“undoubtedly” affected forests of the past.“From sea-level to mountain peaks,‘pristine’ forests have been cut andburned,” she wrote.Forests in the region were also at themercy of climate changes, according toHorn.“Our work helps to inform archaeologicalresearch, and in some cases points topossible changes in climate,” she told TheTico Times. “Understanding past humanactivities and climate can help with effortsto model and predict future climates andenvironments.”HORN’S research at La SelvaBiological Station in the Caribbean lowlandsbelied the idea of untouched, primaryforest in the region, proving that it hadbeen burned and cultivated by prehistoricpeople who had settled there earlier thanprevious studies suggested. Carbon datingof charcoal fragments suggests that humanactivity in the area began over 3,000 yearsago, whereas another archaeological studythat dated ceramic fragments found theretraced human activity to more than 2,000years ago.There is debate over the number ofpeople who inhabited the country beforethe Spanish conquest in the 16th century.Throughout the 1960s, archaeologists heldthat approximately 50,000 people lived inCosta Rica at the height of human developmentbefore the Spaniards’ arrival. In1980, historians suggested the number wascloser to 400,000. Maureen Sánchez, anarchaeologist at the University of CostaRica (UCR) who has worked with Horn, isskeptical of that number.“We would have to do a study on howmany people a place would support usingindigenous agricultural techniques,”Sánchez said. “Historians gave the answer(in 1980), not archaeologists.”She and Horn plan to embark on otherresearch projects together.“We want to better understand howchanges in climate during the Holocene (theperiod between now and the end of the lastice age, about 10,000 years ago) may haveaffected prehistoric societies,” Horn said.She and Ken Orvis, another geographerfrom the University of Tennessee, areresearching the climate history in CostaRican highlands, aiming to link a long-|termhistory of the environment with thearchaeological record.“By comparing findings with our ownwork and that of others elsewhere in theCaribbean, we are trying to figure out howthe climate system has changed over timeand what that portends for future climatechange,” Sánchez said.Her work is funded by the A.W. MellonFoundation, the National GeographicSociety and the National ScienceFoundation.