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Coconuts: not indigenous, but quite at home nevertheless

The views expressed are those of the author and are not necessarily those of Scientific American.


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Coconut palms on the Southern Maalhosmadulu Atoll in the Pacific.

On January 9 in 1878, the Spanish brig Providencia was en route from Cuba to Spain, but would never arrive at this destination. Although the weather was clear that day, the ship wrecked off the shores of Florida. Its cargo, 20.000 coconuts harvested on the Caribbean island of Trinidad, was scattered along the coast1.

The settlers of Florida knew an opportunity when they saw one and planted some of the stranded coconuts around their homes. The coconut palms and groves that grew from these seeds later gave Palm Beach County its name. Fifty years after the Providencia sank, a reporter of the Palm Beach Post wrote:

“From that wreck has grown the palms that line the streets and parks of Palm Beaches. [..] 20.000 coconuts provided the beginning of trees not indigenous to the area, but quite at home, nevertheless.”
~ Palm Beach Post, Nov 20 1938

Not indigenous, but quite at home. This description not only fits the palms that sprang from Providencia‘s wreck, it’s true for coconut palms around the world. Although coconut palms now adorn the coasts of tropical beaches everywhere, from the Caribbean to Madagascar and Hawaii, the tree is not a native species there. All these palms, like the palms of Palm Beach, were introduced by humans.

Coconut palms can be found on every tropical coast, although they are not native there.

Humans have always been eager to bring coconuts along on their travels, and for good reasons. Coconuts are not only a source of both food and water, different parts of the coconut palm can also be used for other purposes. Alcohol and sugar can be extracted from its sap, and cocos oil from the nut itself, for example. Today, they grow on both sides of the Atlantic and Pacific ocean. But where did this useful crop first come from?

Since coconut palms have been crossed, cultivated and transported for thousands of years, retracing the coconut’s path through archaeological sources alone is difficult. The coconut’s collective history has been preserved far better inside its DNA. By mapping the relatedness of coconut palms around the globe, it is possible to reconstruct the tale of their expansion. Last month, Kenneth Olsen and colleagues published a thorough analysis of coconut DNA in PLoS ONE from 1322 coconut palms around the world.

These coconuts are being dried to make copra, from which cocos oil is made

The team discovered that despite the coconut’s complicated history, the underlying genetic structure of coconut populations is simple. Most coconuts belonged to one of two genetically distinct groups. One population traces back its ancestry to palms on the coasts of India, the other group descended from palms in Southeast Asia. Even palms that now grow on the other side of the world are still members of one of these two groups. Palms in Middle America are mostly of the Pacific variety, whereas Caribbean palms belong to the Indian group, for example.

Since the genetic differences between the Indian and Pacific varieties are so numerous and clear, the two lineages must have been evolving in separate directions for a long time. For this reason, Olsen’s team concluded that the coconut palm was not domesticated once, but twice: in India and on the Malay Peninsula. Following the Pacific domestication, settlers would have brought the coconut to the Polynesian islands. Austronesian seafarers from the Philippines later introduced the coconut to the Pacific coast of Middle America. The coconut palms that were domesticated in India spread westwards. After they had been introduced in East Africa, Europeans brought the coconut to the Atlantic coast of Africa and later to South America.

The two lineages not only differ genetically, there are also biological differences. The fruit of the Indo-Atlantic palms are more elongated and angular compared to the rounder, Pacific fruits. In earlier theories about coconut evolution, palms bearing elongated fruits were seen as wilder plant, whereas the trees with rounder fruits were supposed to be ‘more domesticated’. Since the two types of palm arose from independent domestications, this theory no longer holds. Rounder fruit did not evolve from angular fruit in a linear fashion.

These coconut fruits are of the rounder ('niu vai') type.

Of course, the evolutionary history of coconut palms is not just a matter of Indian versus Pacific coconuts. Evolution never deals in black and white. The genetic differences between both varieties are not absolute. Some coconut trees, like those on Madagascar, are genetic mixtures of the Pacific and Indian varieties. At some point the two groups must have interbred and produced offspring on the African island.

Since Madagascar is an island in the Indian Ocean, so the Indo-Atlantic heritage of Madagcasar’s palms is no surprise. The Pacific ancestry is more confusing though. Coconut palms on the Seychelles, an island group just north of Madagascar, contain few traces of Pacific ancestry So how did Pacific coconuts get to Madagascar?

The answer, again, involves human migration and trade. The people of Madagascar themselves partly descend from Southeast Asian ancestors. To explain this genetic mixing of people and coconuts, geneticists and anthropologists suggest that seafarers from the Malay archipelago frequented Madagascar on their trade routes to East Africa. Perhaps some of these traders and their coconuts eventually settled in Madagascar. Arab traders could also have played a role in the dispersal of Pacific coconuts. Arabic influences on East Africa are evidenced by the spread of Islam and introduction of Asian crops in this region. The Seychelles were never part of the Malay and Arabian trade routes, which explains why these palms have no Pacific heritage.

Next time you see a coconut palm, I hope you’ll realize that is more than just a fancy tree with tasty seeds on a tropical beach. The coconut’s evolutionary history is intertwined with the complex history of human migration, trade and colonization. That’s not bad, for a humble seed far from home, but quite at home nevertheless.

The genetic composition and spread of coconut palms around the world


Images:
Coconut palm by Sykez
Coconut distribution by Niklas Jonsson.
Drying coconuts by Dan Iserman
Golden coconut fruit by DeusXFlorida
Spread of coconuts around the world from second reference.
References:
Oyer H (2001), The wreck of the Providencia in 1878 and the naming of Palm Beach County, Vol. 29, South Florida History
Gunn BF, Baudouin L, & Olsen KM (2011). Independent Origins of Cultivated Coconut (Cocos nucifera L.) in the Old World Tropics. PloS one, 6 (6) PMID: 21731660

Lucas Brouwers About the Author: Lucas Brouwers is fascinated by evolution. He writes about science on his blog and for a Dutch daily newspaper. Follow on Twitter @lucasbrouwers.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. EricMJohnson 9:38 am 08/1/2011

    So, what you’re saying then, is that it was neither African nor European swallows. Interesting theory. May I ask your favorite color?

    Link to this
  2. 2. Grumpyoleman 4:28 pm 08/1/2011

    Interesting conjecture. One would have thought that the coconut palms’ distribution would be based on the ocean drift of pods and seeds.

    Link to this
  3. 3. Lucas 11:29 am 08/4/2011

    @Eric: I’m well aware of the ongoing discussions regarding the role of swallows in coconut dispersal. The thing is, African swallows don’t migrate and European swallows would’t be able to carry a coconut if their live depended on it. Oh, and blue!

    @Grumpyoleman: You touch upon a good point. Clearly, the coconut is well adapted to a life at sea, and there’s no question about it that the seed naturally disperses via the ocean.

    The role of human activity should not be underestimated however. While there still could be ‘wild’ coconut palms around, by now they will have interbred with domesticated varieties. In 1992, Harries wrote: “A “pure” wild or domestic palm population, or even individual palm, will be very unlikely following the intense activity in planting and disseminating coconuts for nautical, mercantile or agricultural uses.”

    (source: http://lib-ojs3.lib.sfu.ca:8114/index.php/era/article/viewFile/36/24)

    Link to this
  4. 4. david winter 6:26 am 08/9/2011

    Nice write-up of an interesting paper Lucas.

    I’m a little suprised they didn’t spend a bit more time talking about the evidence that coconuts can get about on their own too. There are fossil fruits from Australia and (amazingly) here in New Zealand (another species with much smaller fruits). But more interestingly many islands have fossil coconut pollen starting much earlier than the first evidence for human habitation. That’s a little tricky again, because Polynesians often visited islands before they settled them, and would even ‘seed’ them with food plants. But it many cases the gaps are very large.

    It’s looks like the fine-scale distribution of coconuts will turn out to have been driven by a mixture of human efforts and the coconuts own buoyancy. (The few times I’ve stood on tropical beaches I’ve always wanted to pick up the coconuts, genotype them and see if there were any that had come from far way – basically what my office-mate does with kelp http://dx.doi.org/10.1111/j.1365-294X.2010.04842.x – sadly these results suggest that would work!)

    Link to this
  5. 5. mr.coconutpalm 2:44 am 09/24/2011

    I have seen a map of the World showing ocean currents, and there are currents that go westward around the Cape of Good Hope in South Africa. In the summer months, when the water would be warmer, these westward currents could easily carry viable coconuts naturally around the Cape and into the Atlantic from the Indian Ocean to naturally sprout on a tropical beach on the Atlantic coast of Africa or even on an island further out.

    I would say that the widespread distribution of coconut palms throughout the tropics is probably about 50/50. Half from natural dispersion, and half from human introduction in the areas they grow. I live in Texas, and throughout the spring, summer, and early fall, we get hundreds of coconuts watching up on our beaches from Mexico. Some of these nuts are quite viable and will sprout if planted. I have sprouted about a dozen from our Texas beaches. There are only two factors that keep them from sprouting naturally along the southernmost Texas coast (where they will survive the winter, for instance at South Padre Island), and that is the fact that tourists pick them up and some locals chop them open before they have a chance to sprout, and the fact that the south Texas coast is semi-arid, averaging only 26 inches of rain per year, and coconut palms need about 40-60+ inches of rainfall to grow naturally. The winters in Brownsville, Port Isabel, and South Padre are usually mild enough for them to survive there and even produce coconuts if people keep there palms watered to make up for the semi-arid climate. I have seen many coconut palms in the Brownsville area, one about 35ft. tall to the top of the crown, and I have seen one at South Padre that had 47 coconuts on it a few years ago!

    Link to this

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