Thanksgiving Plants

Last week we told you all about the domestication of the chicken-peacock, a.k.a. the turkey. Since there will be many vegetables present on Thanksgiving tables this week, it's only fair to talk about them too! Here are the histories of some of the most popular plants that we love to eat (or love to hate, we don't judge)!

Sweet potatoes, baked and delicious. Photo from: Food Network

Sweet potatoes: Ipomoea batatas, or the sweet potato, was first domesticated somewhere between the Orinoco River delta area of modern day Venezuela and the Yucatán Peninsula in Mexico around 5,000 years ago. The second name of the sweet potato, batata, is the original Taíno word for the plant, though the Quechua people in Peru call it kumar. Surprisingly, it is only distantly related to the white potato, and is a genetically different plant from a true yam. In fact, the sweet potato is fairly closely related to the morning glory flowers, and the flowers of a sweet potato plant are even called tuberous morning glories! As with most of the plants on this list, it was first introduced to Europe via Spanish conquistadors, and to China via Portuguese traders. Sweet potatoes were used around the world to supplement the lack of other food due to poor harvests or other natural events. For example, after the sweet potato was introduced to Japan in the early 1600s, it became an important plant that prevented starvation in years when the rice harvest was poor. It is a popular plant because it grows well and without pesticides in a variety of climates, though it will not survive the cold and requires roughly 36 inches of water a year to grow.

The Three Sisters plants. Image from:
University of Illinois Extension

Squashes and pumpkins: The domestication of squashes and pumpkins (all part of the genus Cucurbita) is one of the best known stories, and one of the oldest: there is archaeological evidence that puts the domestication of squashes before 10,000 years ago! The wild relatives of squashes produce fruit much smaller than what we know today, and the plants were bitter, even toxic. Only the intense domestication efforts of the indigenous people in Central America saved the squashes we enjoy today. These plants are highly adaptable, and grow in many diverse climates. The reason there are so many types is because they have been traded and transported around the world to many different places, and these plants needed to adapt to survive in their new habitats. The English word squash comes from the Naragansett word askutasquash (a green thing eaten raw), excellent evidence that the plant was able to adapt from its Mesoamerican origins to survive in Rhode Island!

An important point is that squash, beans, and corn are called the Three Sisters of plant husbandry because they are mutually beneficial organisms. Basically, they help each other grow so well that the native peoples in the Americas often planted the three of them together! Squash was the first of the Three Sisters to be domesticated, followed by corn and beans.

Corn: Corn was domesticated from maize by the indigenous peoples roughly 10,000 years ago in what is now southern Mexico. The word "maize" comes from the Spanish version of the original Taíno word for it: mahiz. While the consensus used to be that the Tehuacán Valley was the center of domestication, newer analyses show that the the nearby Balsas River Valley is the true origin point of what we know as corn. A study in 2002 showed that modern corn comes from a single domestication event of maize at least 9,000 years ago, and other studies put this date even earlier. Another study argued that knowledge of corn cultivation was spread through two different events thousands of years apart: one event spread corn cultivation down the Andes Mountains around 6,700 years ago, and the second event spread it across the rest of South America roughly 2,000 years ago. It was taken back to Europe by Spanish conquistadors, and quickly became a popular plant around the world because of its ability to grow in many climates, but it is very sensitive to cold and to droughts, and strong winds can uproot it because of its shallow root structure. Today there are many forms of corn, though most of them are grown for industrial purposes (corn ethanol, animal food, etc.).

Beans: Unlike other plants on this list, beans were known in Europe and around the world before any Spaniard set food on the American continents. The beans that are part of the Three Sisters, however, were originally domesticated in (as you may have guessed) Central America. Some bean remains in the Guitarrero Cave in Peru date beans there to 4,000 years ago, though genetic analysis has proved that those beans were merely cultivated there. Beans, along with corn and squash, gradually spread south as knowledge of their cultivation also spread. Beans need support as they grow, and growing them near corn stalks provided that support. Beans in return pull nitrogen from the air and put it in the ground for corn and squash to use. They grow best in the summer and with lots of water. Currently the genetic information for 40,000 species of beans are held in genebanks, but only 30 of those are actually eaten.

Cranberries on a bush. Photo from: FastGrowingTrees.com

Cranberries: Cranberries were domesticated very recently, only about 200 years ago in Cape Cod, Massachusetts. Before then they were wild plants that the Native Americans would collect and use in a variety of different ways, from preserving fish and meat to mixing them into a poultice to use on wounds. Because the cranberry is a relatively young domesticated plant, it hasn't changed much from its wild variety. Cranberries are closely related to blackberries, huckleberries, and the flower rhododendron (that part blows my mind), and distantly related to the fruits kiwi and persimmon. Most cranberries today are grown in the United States, specifically Massachusetts, Wisconsin, New Jersey, Oregon, and Washington, though they are also grown in five provinces in Canada, and parts of Europe and Chile. They are tough plants but do best in wet, cold regions. Cranberries also are high in polyphenolic antioxidants and have some anti-cancer properties. So, eat up!

We here at Science on Main wish you a very happy Thanksgiving, and thank you for reading!

Sources:
 Zhang, D.P.; Ghislain, M.; Huaman, Z.; Cervantes, J.C.; Carey, E.E. (1999). AFLP Assessment of Sweetpotato Genetic Diversity in Four Tropical American Regions (PDF). : International Potato Center (CIP) Program report 1997-1998. Lima, Peru: International Potato Center (CIP). 
 http://bioweb.uwlax.edu/bio203/2011/keesler_cole/
https://www.sciencedirect.com/science/article/pii/S1055790317301811 
https://www.smithsonianmag.com/smart-news/domestication-saved-pumpkin-and-squash-180957314/
"Origin, History and Uses of Corn". Iowa State University, Department of Agronomy. February 11, 2014.
Piperno, Dolores R. (2011). "The Origins of Plant Cultivation and Domestication in the New World Tropics: Patterns, Process, and New Developments". Current Anthropology. 52 (S4): 453–S470. 
Bitocchi, Elena; Nanni, Laura; Bellucci, Elisa; Rossi, Monica; Giardini, Alessandro; Zeuli, Pierluigi Spagnoletti; Logozzo, Giuseppina; Stougaard, Jens; McClean, Phillip; Attene, Giovanna; Papa, Roberto (3 April 2012). "Mesoamerican origin of the common bean (Phaseolus vulgaris L.) is revealed by sequence data". Proceedings of the National Academy of Sciences. 109 (14): E788–E796. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4076063/
 

Movie Science: Alpha

I saw the movie Alpha with friends last Saturday night. When my friends and I go see movies, we whisper to each other the whole time, pointing out flaws in both the plot and the science it implies. Alpha was a rare treat for me: a movie that highlighted large-scale terrain and large, extinct animals. I knew I would like it.

The movie begins with a sequence of landscape shots, some with animals. The first animals we see are woolly mammoths, traveling in a characteristic herd. A few seconds later, a small group of woolly rhinoceros move through what appears to be a glacier-scarred landscape. Hyena and wolf packs prowl and vocalize. Words appear on the screen informing us that the setting is Europe, 20,000 years ago.

With a date and general location, it is now straightforward to examine the science behind the plot. 20,000 years ago puts the movie near the end of the Pleistocene period, otherwise known by its more famous alias, the "Ice Age." There's a lot to say about the science behind the many ice ages of Earth, so we'll save that for another blog post. This one will focus on the animals seen in the movie, and whether or not they belong there.

First up is identifying the animals seen in the opening sequence. Elasmotherium could be the woolly rhinoceros, as it lived in Europe in the Pleistocene, but the youngest fossils date from 29,000 years ago, slightly before the movie's setting. Another genus of animals, Stephanorhinos, also lived in continental Europe around the same time, but it's not as woolly as the ones in the movie, and their horns are a bit short. My guess is that the animals are Elasmotherium, and maybe they are the last of their kind alive. In any case, it checks out.

American Mammoth skeleton on display at the George C. Page Museum. Photo credit: J. Noviello

The most iconic animal of the Pleistocene is the mammoth, and it's no surprise those animals appear early in the film (though it's a shame that they aren't seen again). The oldest woolly mammoth fossils are found in east Asia. From there mammoths migrated out, eventually evolving into a few different species. Europe was definitely one of those places, as their bones are fairly common in many countries, and mammoths are seen in cave paintings made by ancient humans. While most mammoths were extinct by 10,000 years ago, small populations of isolated animals may have survived until as late as 4,000 years ago. One quick note is that the mastodon is a totally different animal from the mammoth, and only found (so far) in north and central America. This one too checks out.

The humans in the movie (which are very likely true Homo sapiens, even though Neanderthals certainly inhabited the area) are first seen hunting buffalo. This checks out as well, as there are many different species of bison in the Pleistocene fossil record. The length and curvature of the horns, as well as the size of the bison itself, at first made me think of Bison latifrons, but that animal only lived in North America. A better choice for the buffalo hunted in the movie is the steppe bison, Bison priscus, as it was a widespread species and definitely lived in Europe; it also makes many appearances in cave paintings, especially at the Cave of Lascaux in France. This checks out too.

From: https://www.lascaux.fr/en/prepare-your-visit/visit-lascaux/lascaux-2

Wolves and hyenas also check out, though the animals seen in the movies are their modern-day counterparts. Cave hyenas were massive, about twice the size of extant hyenas. Judging from the presence of bones in different caves, it appears that cave hyenas and humans actively hunted each other, or at least scavenged from each other's kills. These hyenas lived across Europe and Asia until about 20,000 years ago, after which their populations severely declined. In any case, this too checks out. Of course wolves check out because we know that dogs are descended from wolves, so the question becomes what kind of wolves these are. While I initially thought they could be dire wolves, they are only found in North America. The wolves in the movie are probably simple cave wolves.

Finally, there is the closest thing to a villain in the movie: the saber-tooth cat. While we only are ever shown a shadowy outline of the beast that kills a hunter early in the film, its profile is unmistakable. Sabre-tooth cats (the most famous of which is Smilodon fatalis, though there are a few) were fearsome predators that went extinct about 10,000 years ago, so the timeline checks out. Now onto where they lived. The most famous location for their bones is the La Brea Tar Pits in Los Angeles, California, but they are found as far south as Argentina. While saber-tooth cats were thought to be extinct in Europe as early as 300,000 years ago, a new jawbone discovered in the Netherlands has been dated to as late as 28,000 years ago, significantly later than what scientists originally thought! Therefore, while it is far more likely that saber-tooth cats lived in the Americas around the time of the movie, it is not impossible they were also in Europe. This checks out, albeit tenuously.

Maybe it's because I'm a scientist at heart, and that prehistoric animals are very close to my heart, but while watching this movie, I automatically evaluated it. I try to remember that it's been made for entertainment purposes, not for education. Even so I can appreciate attention to detail, and I think Alpha did a good job overall representing the paleobiology of Pleistocene Europe. And, if I may say so myself, the movie itself was good too.

Sources:
https://www.nature.com/news/sabre-toothed-cats-prowled-europe-200-000-years-after-supposedly-going-extinct-1.22861
https://en.wikipedia.org/wiki/Cave_hyena
https://en.wikipedia.org/wiki/Steppe_bison
https://en.wikipedia.org/wiki/Megafaunal_wolf#cite_note-goldfuss1823-4
https://en.wikipedia.org/wiki/Woolly_mammoth
https://en.wikipedia.org/wiki/Elasmotherium