The calabash (Legenaria siceraria) is a very handy fruit used by numerous cultures from around the world. However, scientists have always wondered how the calabash spread from its initial home in Africa to the rest of the world.
The calabash, also known as the bottle gourd, is one of the first plants to be cultivated by humans for purposes other than eating. Unlike most fruits, the calabash can be used for a wide variety of things. It has been used to make pipes, water containers or even utensils.
Archeologists have determined that the calabash were cultivated in North and South America as early as 10,000 years ago or well before the arrival of Columbus. However, scientists have been wondering how it got there considering that the Atlantic Ocean lies between Africa and the Americas.
Previous theories regarding the spread of the bottle gourd to the Americas postulated human action. However, a new study indicates that the humble calabash may have traveled to the New World on its own. How? By floating across the Atlantic.
By analyzing data about ocean currents as well as the genetic makeup of the calabash, researchers were able to theorize that the calabash may simply have floated across the Atlantic, ending up in the Americas. If the theory holds up, scientists believe that the results could very well shed light on the mystery of the development of agriculture in the New World.
Back in 2005, a paper was published indicating that the bottle gourds in the Americas are closely related to their Asian counterparts. The researchers who worked on the paper theorized that humans brought bottle gourds from Asia to North America using the Bering land bridge. However, this theory has a big flaw, according to University of Warwick plant biologist Andrew Clarke. The bottle gourd is primarily a tropical fruit. Since the human migration to North America took years to complete, how could a tropical plant survive in Arctic conditions?
To answer these lingering questions about the bottle gourd's appearance in the Americas, Pennsylvania State University anthropologist Logan Kistler determined that the 2005 paper merited further study. Back in 2005, researchers used three genetic markers to come to their conclusion about the bottle gourd's origins. Due to the availability of new genetic technologies, the researchers who revisited the study analyzed 86,000 base pairs obtained from both modern and ancient calabash chloroplast DNA.
"Our findings overturn a major component of the current model for bottle gourd's early global dispersal, specifically regarding how it entered the Americas," said Kistler and his colleagues. "Our findings also indicate that the domestication process itself took place in a diffuse pattern throughout the bottle gourd's New World range, explaining early and nearly contemporaneous use of bottle gourds in North, Central, and South America."
The analysis of chloroplast DNA in plants can be likened to the analysis of mitochondrial DNA in humans. Using chloroplast DNA, the researchers were able to construct a family tree for the plants to determine their ancestry. The researchers found that the pre-Columbian bottle gourds were actually closely related to the gourds from Africa. This means that the land bridge theory was highly unlikely.
To complete the new study, the researchers also took a close look at the ocean currents flowing between Africa and the Americas. They determined that the bottle gourd probably floated down an African river ending up in the coasts of West Africa. From there, the bottle gourd may have floated to America via Atlantic currents.
While the new study provides an interesting and highly probably theory regarding the spread of the bottle gourd from Africa to the Americas, many unanswered questions still remain. For instance, scientists are still at a loss regarding how the bottle gourd ended up in Asia. Answering these questions is difficult due to the fact that hardly any sample of bottle gourds can now be found in the wild.