The hot and humid lowland tropical forests of Mexico's southern Gulf coast seem an unlikely environment to nurture early steps to civilization. However, from about 1150 to 500 BC that region's riverine floodplains and adjacent low uplands were the domain of the Olmecs, whose magnificent stone monuments and ancient ruins lay hidden for centuries beneath jungle vegetation. Eight years of research, initiated in 1938 by Smithsonian archaeologist Matthew Stirling, uncovered fabulous Olmec stone carvings, jade objects, and mound architecture. Coming from a region commonly thought inhospitable and marginal, the finds perplexed scholars. More perplexing was the great antiquity Stirling assigned to his discoveries. The sophistication of the Olmecs seemed out of place in both time and space. While their apparent precocity soon led scholars to perceive them as Mesoamerica's first civilization and "mother culture" to all of its later civilizations, the origins of their complexity, and of the Olmecs themselves, seemed puzzling.