The evolution of teosinte into modern corn, known as maize, represents a profound transformation in plant history. This journey began with a wild grass that, at first glance, bears little resemblance to the staple crop we recognize today. The remarkable changes over millennia highlight the power of human selection in shaping the natural world.
Teosinte: The Wild Ancestor
Teosinte, Zea mays subspecies parviglumis, is the direct ancestor of modern maize. It grows wild in the Central Balsas River Valley of Mexico, thriving in moist habitats along streams and hillsides. This wild grass presents a stark contrast to cultivated corn.
A teosinte plant is highly branched, producing numerous long side branches, each ending in a tassel. These branches also bear multiple small “ears,” each containing about 5 to 10 kernels arranged in two rows. The kernels are encased in a hard, protective fruitcase, making them difficult to access and consume. When mature, these small ears naturally shatter, dispersing the seeds.
The Transformation: From Teosinte to Maize
The domestication of teosinte into maize was a gradual process spanning thousands of years, driven by human selection. Early Mesoamericans likely selected plants with traits that made them easier to harvest and consume, initiating dramatic phenotypic changes.
One significant change involved the plant’s architecture. Teosinte’s highly branched structure evolved into the single-stalked plant characteristic of modern maize, with short lateral branches each bearing a single, large ear. This shift from many small ears to one or two large ears with hundreds of kernels greatly increased yield and harvest efficiency. The hard, protective fruitcases surrounding teosinte kernels were replaced by soft, exposed kernels on the cob, making them readily edible. The non-shattering nature of the maize cob, where kernels remain attached, is another key domesticate trait, ensuring the harvested grain stays intact.
Genetic Underpinnings of Maize Evolution
The visible changes from teosinte to maize are controlled by a relatively small number of genetic modifications. Scientists have identified specific genes that played a pivotal role in this transformation. These genes had significant effects on key traits.
One gene is teosinte branched1 (tb1), which controls the plant’s architecture. In teosinte, the tb1 allele promotes extensive branching, while in maize, it leads to a single, unbranched stalk by repressing axillary bud growth. The maize allele of tb1 is expressed at higher levels than its teosinte counterpart, contributing to its reduced branching.
Another gene is teosinte glume architecture1 (tga1), responsible for the shift from encased to naked kernels. A single nucleotide change in the tga1 gene in maize alters the protein’s function, leading to smaller, less enclosing fruitcases and exposed kernels. These examples illustrate how small genetic changes can lead to profound morphological differences.
Significance of Maize’s Evolutionary Journey
The domestication of maize represents a monumental achievement in human history, fundamentally altering agricultural practices and the development of civilizations. Maize became a staple food for many cultures throughout the Americas, including the Olmec, Maya, Aztec, and Inca, sustaining large populations and influencing their societal structures, art, and mythology.
From its origins, maize spread throughout the Americas, reaching South America within 1,500 years and eventually traveling north to what is now the southwestern United States. Its adaptability allowed it to thrive in diverse environments, leading to the development of numerous local varieties. Following the Columbian Exchange in the 16th century, maize spread globally, becoming one of the most widely cultivated and economically significant crops worldwide. This journey underscores how human ingenuity, through selective breeding, transformed a wild grass into a global food source.