Maize, commonly known as corn, is a towering grass that yields a cereal grain, making it one of the world’s most widely grown and consumed crops, surpassing both wheat and rice in total production volume. The plant is a foundation of the global food system, providing animal feed, biofuels, industrial ingredients, and a staple food for billions of people. Tracing the origin of this important plant is a major achievement in modern botany and archaeology, revealing a fascinating evolutionary journey that began thousands of years ago with a seemingly insignificant wild grass.
Teosinte The Wild Ancestor
Modern genetic and archaeological evidence points to a wild grass called teosinte (Zea mays ssp. parviglumis) as the ancestor of maize. Early in the 20th century, the relationship between the two plants was highly debated because of their starkly different physical appearances. Teosinte is a short, bushy plant that grows many long side branches, each often culminating in a tassel.
The teosinte ear is vastly different from a modern corn cob, possessing only a handful of small kernels arranged in two rows. Each kernel is encased in an extremely hard fruitcase that must be cracked open to access the grain. This protective casing makes the plant inefficient for human consumption. The ability of teosinte’s kernels to readily detach from the stalk, a process called shattering, also made harvesting difficult.
Geography and Timeline of Domestication
The transformation of teosinte into the earliest forms of maize began in the tropical lowlands of southwestern Mexico. The Balsas River Valley is identified as the geographical cradle of maize domestication, a conclusion supported by genetic analysis and archaeological findings. The Balsas teosinte subspecies is the wild relative most genetically similar to domesticated maize, confirming this location as the point of origin.
The domestication process started approximately 9,000 years ago, placing it among the most ancient examples of plant cultivation in the Americas. The oldest microremains of maize have been recovered from the Xihuatoxtla rock shelter in the Balsas Valley, dating back about 8,700 years. These findings suggest that early farming communities in the region were already engaging in the selective cultivation of teosinte, even if it had not yet become a primary staple food.
Key Genetic Changes Transforming Teosinte into Maize
The differences between teosinte and maize are largely attributed to the selective breeding of a small number of key genetic mutations. Early farmers selected for traits that made the plant easier to harvest and the kernels easier to consume. One of the most significant changes was the loss of the hard, inedible fruitcase surrounding each kernel, resulting in the “naked” kernels of modern corn.
This dramatic change is controlled primarily by a single gene called teosinte glume architecture 1 (tga1). A mutation in this gene resulted in the soft glume, allowing the kernels to become larger and accessible without needing to be cracked open.
Another major mutation occurred in the gene teosinte branched 1 (tb1), which controls the plant’s branching structure. By selecting for a mutation in tb1, early cultivators gradually suppressed the numerous side branches, shifting the plant from a bushy form to a single, main stalk with ears.
Selection for increased seed retention, or the loss of the shattering trait, was also a major step. This ensured that the kernels remained attached to a central cob, allowing for a much larger and more efficient harvest. The cumulative effect of these few genetic switches, driven by human selection, transformed the wild grass into a highly productive food source.
Global Dissemination and Early Cultivation
Once domesticated, maize migrated out of its center of origin in Mesoamerica, spreading both north and south across the Americas. Archaeological evidence indicates that maize reached the highlands of Ecuador at least 8,000 years ago and was present in Panama by 5,500 BCE. It arrived in the American Southwest around 4,100 years ago, though it did not become a staple crop in that region until much later.
The successful cultivation of maize supported the rise of complex societies throughout the Americas. Civilizations such as the Olmec, Maya, and Aztec relied heavily on maize agriculture, which enabled the development of large, settled populations and monumental architecture. Following the arrival of Europeans in the late 15th century, maize was introduced to the rest of the world as part of the Columbian Exchange. Due to its adaptability, it quickly thrived in the warmer climates of Southern Europe, Africa, and Asia, becoming a staple crop in many new regions.