Evolutionary and food supply implications of ongoing maize domestication by Mexican<i>campesinos</i>

Abstract

Maize evolution under domestication is a process that continues today. Case studies suggest that Mexican smallholder family farmers, known as <i>campesinos</i>, contribute importantly to this, but their significance has not been explicitly quantified and analysed as a whole. Here, we examine the evolutionary and food security implications of the scale and scope under which <i>campesinos</i> produce maize. We gathered official municipal-level data on maize production under rainfed conditions and identified <i>campesino</i> agriculture as occurring in municipalities with average yields of less than or equal to 3 t ha^-1 Environmental conditions vary widely in those municipalities and are associated with a great diversity of maize races, representing 85.3% of native maize samples collected in the country. We estimate that in those municipalities, around 1.38 × 10¹¹ genetically different individual plants are subjected to evolution under domestication each season. This implies that 5.24 × 10⁸ mother plants contribute to the next generation with their standing genetic diversity and rare alleles. Such a large breeding population size also increases the total number of adaptive mutations that may appear and be selected for. We also estimate that <i>campesino</i> agriculture could potentially feed around 54.7 million people in Mexico. These analyses provide insights about the contributions of smallholder agriculture around the world.