Regulating the Regulators continued funding. Few archaeologists were willing to search for the origin of plant cultigens in lowland and jungle regions, where seeds, wood, rinds, and cobs did not preserve well. Many also wondered how tropical lowlands could have supported foragers making the switch to early sedentary farming. And most believed incorrectly that all lowland and jungle soils were infertile, similar to ones known from the non–flood plain regions of the Amazon. But Piperno and a few others remained convinced that the long search for cultigen origins had focused on the wrong areas and the wrong kind of clues.

It is true that, except for charcoal, the visual evidence of plant remains quickly disappears in most tropical soils. But some clues remain, if you know where to look. By the early 1990s, Piperno (2, 6) had shown that plant phytoliths were plentiful in the lowland soils of many regions of Central and South America. She noted that the size and shape of phytoliths were often unique to a family, genus, or species of plant (see panel A of the figure). Piperno and Pearsall then led the way in developing phytolith keys to a wide variety of New World cultigens and tropical plants (5). Armed with this knowledge, scientists began to search for microscopic clues in the soils of early, well-dated archaeological sites throughout Central and South America.