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Fossil sheds new light on the history and evolution of chili peppers

In a surprising twist of events, researchers at the University of Colorado Boulder have identified an ancient chili pepper fossil, which could cause a seismic shift in our understanding of the geographical origins and evolutionary timeline of the tomato plant family.

The University’s research was backed by the U.S. National Science Foundation and is published in the journal New Phytologist. The study reveals that the chili pepper tribe (Capsiceae), a part of the tomato, or nightshade (Solanaceae) family, is significantly older and its geographic reach much wider than previous theories suggested.

Previously, the prevailing belief among scientists was that chili peppers evolved in South America no more than 15 million years ago. However, this new research stretches the origin of chili peppers back by 35 million years, to an impressive 50 million years ago. It even goes so far as to suggest that North America was home to chili peppers during that era.

Accidental discovery

It was an ordinary day at the CU Boulder Museum of Natural History for Rocío Deanna and Abel Campos, but what they found was extraordinary. Amidst a collection of specimens from the Green River Formation – a geologically rich site stretching across northwestern Colorado and southwestern Wyoming – Deanna observed a distinctive feature of the solanaceous family etched in a fossil: tiny spikes on the end of a fruiting stem.

Having found two such fossils at CU Boulder, Deanna and Campos, a collaborator on the study, came across a third specimen from the chili pepper tribe housed at the Denver Museum of Nature and Science. All three fossils traced back to the Green River Formation in Colorado – the CU fossils hail from Garfield County, and the DMNS specimen from Rio Blanco County.

Katharina Dittmar, a program director in NSF’s Division of Environmental Biology, emphasized the significance of the study. “This research nicely highlights the importance of natural history collections in calibrating the timeline of evolution, in this case, of an agriculturally important plant family.”

Could chili peppers have existed 56 million years ago?

These newly identified chili pepper fossils belong to the Eocene geological epoch (34 to 56 million years ago). Intriguingly, their timeline matches that of another nightshade fossil from the Esmeraldas Formation in Colombia. This simultaneous existence suggests that the nightshade family had a pan-American distribution as early as 50 million years ago.

The nightshade family is vast, encompassing around 3,000 species and nearly 100 genera, including chili peppers. Fascinatingly, the ancient chili pepper was technically a fruit – and a berry at that. Despite the common association of tomatoes and peppers with vegetables, their internal seed-bearing structure categorizes them as fruits.

“The world has maybe 300,000 plant species,” said study senior author Stacey Smith. “The only plant with that kind of calyx is this group of 80 or 90 species.”

Previous assumptions held that chili peppers emerged in South America about 10 to 15 million years ago and gradually spread across the globe through terrestrial and aquatic means. 

Although modern Colorado has scant native nightshades and no chili peppers, this groundbreaking discovery implies that a diverse array of tomato plant family members could have thrived in North America 40 to 50 million years ago, only to largely vanish in subsequent eras.

Theory proposed by the research team

A theory has been proposed that fruit-eating birds, which have existed for at least 60 million years, might have inadvertently acted as seed carriers, transporting plant species globally via their digestive systems, plumage, or foot-borne mud.

These prehistoric avian travelers needed nourishment for their migrations, and what could be more suitable than juicy berries, or peppers? It appears that not only might birds have facilitated the spread of peppers from continent to continent, but peppers themselves could have been instrumental to the survival and success of these birds. This symbiotic relationship could have driven the early dispersion and evolution of the chili peppers.

Stacey Smith expressed her fascination with the new insights: “These chili peppers, a species that we thought arose in an evolutionary blink of an eye, have been around for a very long time.” This research has effectively transformed our understanding of the evolutionary journey of chili peppers.

In conclusion, this unexpected discovery of ancient chili pepper fossils in Colorado has upended existing theories about the origins and dispersion of the nightshade family. It highlights the crucial role of natural history collections in shedding light on the evolution of plant species, and underlines the intriguing, interwoven relationships that exist in nature – between plants and animals, and even between continents. This knowledge will undoubtedly pave the way for further research into the fascinating history of the world’s plant species.

More about chili peppers

Chili peppers are a staple in many cuisines around the world today. They belong to the genus Capsicum and are a part of the nightshade family, Solanaceae. 

Modern chili peppers come in a variety of shapes, sizes, colors, and, of course, heat levels, which are caused by the presence of a compound called capsaicin. The hottest part of a chili pepper is actually the white pithy part inside the pepper, not the seeds as commonly believed.

Chili peppers are widely known for their medicinal and health benefits. They are rich in vitamins and minerals such as vitamin C, B6, A, and potassium. They also have antioxidant properties and are known to boost the metabolism, aid digestion, relieve pain, reduce inflammation, and possibly even prevent cancer.

The Scoville scale

The heat of a chili pepper is measured on the Scoville scale, named after American pharmacist Wilbur Scoville, who invented it in 1912. This scale measures the pungency or spicy heat of chili peppers in Scoville Heat Units (SHU). 

This measurement originally depended on the human taste test but has since been replaced by more objective, instrumental methods, such as high-performance liquid chromatography (HPLC).

To give you a sense of the Scoville scale, bell peppers, which contain no capsaicin, have a Scoville rating of zero, while a Jalapeno pepper ranges from 2,500 to 8,000 SHU. At the top of the scale are the world’s hottest peppers, such as the Carolina Reaper, which can reach over 2 million SHU. Consuming these super-hot peppers can cause severe discomfort and should be done with caution.

Despite their heat, chili peppers are a beloved ingredient around the world, adding not just spice, but flavor, color, and health benefits to countless dishes. From the mild bell pepper to the fiery Carolina Reaper, the diversity and global popularity of chili peppers are a testament to their unique appeal.


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