Prehistoric humans helped spread edible fruit species across Central and South America, even as they wiped out the megafauna that had done so previously. In the process, we maintained and even expanded the plants’ habitats, increased biodiversity, and engineered ecosystems on two continents. Today, these fruit species could be important in 21st-century efforts to diversify human diets, address food scarcity, and improve agricultural sustainability.

Fruiting plants have evolved a very solid strategy for getting their offspring out into the world. Animals eat the fruit, they drop the seeds, and the next generation of plants takes root, often quite a distance away from their parents. Before about 12,000 years ago, animals like the giant sloth, elephant-like mammals called gomphotheres, and native horses did most of the work of seed dispersal in Latin America.

When those animals died out around the end of the Pleistocene, many of the fruit species they’d helped spread found their ranges contracting. But as the early Holocene climate shifted toward warmer, wetter conditions, humans picked up the slack in a big way for some fruit species.

Take gourds, for example. Domesticated or even partially domesticated species spread widely after the die-off of Latin America’s megafauna. In contrast, their wild relatives’ range actually shrunk once the megafauna weren’t around to scatter their seeds anymore.

Bioscientist Maarten van Zonneveld of the World Vegetable Center and his colleagues compared three groups of Latin American fruit species once eaten and dispersed by now-extinct megafauna: species never eaten by humans, wild species eaten by humans, and domesticated species. (We know, for the most part, which species humans eat thanks to a lot of ethnobotanical, genetic, and archaeological research—there’s actually a database of all the fruits people in the New World eat.) It turns out that the fruits people eat have much wider geographic ranges than those we don’t. And when you look at plants that humans have deliberately cultivated, those ranges are even broader.

Fruit species that managed to appeal to the all-important human demographic were also found in a wider range of rainfall conditions, which probably points to people spreading plants outside their normal habitats. In doing so, they may be selecting—accidentally or on purpose—for varieties that could survive in the shifting Holocene climate or in a wider range of places.

Looking at the data makes clear that people have shaped Latin America’s ecosystems on a large scale. The significance of that becomes even clearer when you consider that fruit-bearing plants help store carbon and move nutrients around ecosystems in important ways, so the impact goes far beyond which fruits are available to eat in which spots.

How picky eaters promote genetic diversity

All that human meddling generally increases the genetic diversity of the plants involved. Humans are picky eaters, so we tend to eat fruit that’s appealing in some way, whether because of taste, texture, appearance, amount of actual fruit compared to rind and seeds, or willingness to grow in the right places. Because we typically only drop seeds from fruits we eat, that choosiness gradually selects for different combinations of traits people want. The effect is even more noticeable in domesticated species, where pre-Columbian farmers deliberately bred plants for certain traits.

The result is a lot more diversity in human-modified species than in wild ones.

“In a similar way, heirloom varieties of apple, tomato, and maize varieties express wide ranges of fruit shapes and tastes that are of interest to humans after centuries or maybe millennia of conscious and unconscious selection by humans,” said van Zonneveld.

He argues that genetic diversity is an important resource for efforts to address challenges like food scarcity and agricultural sustainability because it provides source material for breeding better varieties of existing species. His work also provides a roadmap for domesticating wild fruit species or introducing new ones. And researching how humans helped shape the diverse flora of Latin America is the first step in figuring out how to conserve it.

“Understanding the history of fruit species’ dispersal will help to target areas for conservation in national parks and in farms, as well as germplasm collection for conservation in gene-bank collections for breeding and long-term conservation,” said van Zonneveld.

One example is the cherimoya, a species of custard apple. In an earlier study, van Zonneveld and his colleagues mapped its genetic variation and traced signs of human impact.

“On the basis of this analysis, we were able to target areas for conservation in the center of species origin where extinct megafauna dispersed the species, as well as in Mexico and South America where humans incorporated the species in their food systems,” said van Zonneveld. “We have started to contact national institutes in Central and South America to discuss what would be best strategies for conservation in each country.”

Try new foods—or really old ones

Convincing people to eat more native fruits, including those first spread by indigenous people, could help promote more environmentally sustainable food production and more diverse diets. More diverse diets, in turn, are less vulnerable to crop failures and shifting climate than systems where most of a country’s nutrition depends on a small handful of crops.

That’s become a priority in Brazil, where the national government now defines and recognizes “Brazilian Sociobiodiversity Native Food Species of Nutritional Value.” Under its commitment to the United Nations Convention on Biological Diversity, Brazil’s National Biodiversity Strategy and Action Plan includes “the utilization of native plant species with actual or potential economic value as a successful measure of biodiversity conservation.” And in Peru, chefs like Gaston Acurio and Virgilio Martinez are promoting native plant species and traditional farming as part of their high-end gastronomy, with a focus on native potato, hot pepper, and corn varieties.

Other long-neglected species that are now getting more attention include custard apples like cherimoya and lucuma, cashew relatives, and zapotes. Many varieties of these fruits, along with several fruit palm species, were once eaten by native people throughout Latin America. But they mostly fell into disuse outside remote indigenous communities around the time of European contact, largely because the people who were eating them ended up exposed to diseases like smallpox, as well as violence and forced cultural assimilation at the hands of European colonists. The death of three-quarters of Latin America’s indigenous population radically altered the culture of many survivors.

Of course, changing people’s eating habits isn’t easy, but it’s happened before. In Europe, for instance, one of the consequences of colonization was that people started eating tropical fruits and spices that weren’t on the menu just one or two generations before. And the idea isn't limited to Latin America; van Zonneveld and his colleagues say researchers, governments, and private organizations should study, preserve, and utilize the genetic diversity of native plants on every continent.

“One way in which researchers can contribute is to inform people about the richness of food plants in their own countries and the culture heritage in nearby villages and natural parks. Many adults and children who live in the cities are not aware of all the fruit and vegetable species that have been part of human diets in their countries,” said van Zonneveld. “Realizing that these food plant species exist is the first step before adults and children try them out, eat them, and maybe incorporate them in their diets on a regular basis.”

PNAS, 2017. DOI: 10.1073/pnas.1718045115 (About DOIs).