Evolution in the Deepest River in the World

New species are born in the turbulence of the Congo River

  • By Kyle Dickman
  • Smithsonian.com, November 03, 2009, Subscribe
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Lower Congo River
A view upriver on the lower Congo River. (Skip Brown)

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Dr Melanie Stiassny with Elephant Fish

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"These are elephant fish," Stiassny says. "Their jaws are at the end of their snouts so they can pick food from the gravel."

The evolutionary adaptations are apparent. Each individual was caught in a different location, and each snout is specialized to the character of the river floor in which it fed. Long and thin snouts allow fish to probe for food in deep and small-grained gravel; short and fat snouts allow them to feed on algae-caked bedrock. "Darwin's fishes," Stiassny says.

A series of mud-colored minnows caught in different locations that look identical to me excite Stiassny. "That's really where we see evolution in action," Stiassny says. "In 50 or 100 years, the fish that look the same today may well look different. We can see the start of that genetic drift."

That night, Gardiner plugs a data card in his laptop. Winged insects flock to the glowing screen, their buzzing mostly drowned out by the steady drone of the river and the occasional whoosh of its surge breaking on the beach. The computer hums while processing data. Eventually Gardiner pulls up a graph profiling the river's bed. It looks like a U—as smooth as a mountain valley carved by a glacier. The current just beneath the surface is traveling at 30 miles per hour, and the channel is 640 feet deep.

"That's the deepest point measured on a river in the world," Gardiner says. "There's no question about that."

Shelton is peering over Gardiner's shoulder, shaking his head and deciphering blue and red lines on the computer screen that represent water movement and velocity.

"Just like we thought," he says. "Fabulous stuff." He nudges a moth off the screen and points to a place in the riverbed where a long blue line indicates the current dropping vertically from a ledge into the canyon's trough.

"It's an underwater waterfall," he says, slapping Gardiner's shoulder. It's falling at 40 feet per second. Upstream of the waterfall is an eddy, the water relatively still. This point is likely habitat for the blind cichlid: calm pockets where sheering currents have trapped the fish at great depths. Deep-river specimens, like the one found today, surface only when the river surges and flushes individuals into the harsh environment of the main flow. In terms of Stiassny's hypothesis, the finding suggests that the Congo's currents partition habitat from side to side and from top to bottom—just like a mountain range.

"It shows water can be an evolutionary barrier, even for fish," Gardiner says.


Ned Gardiner, a scientist who specializes in mapping ecosystems, is fiddling with an instrument floating over the side of our wooden pirogue when the boat emerges from an eddy into the main stream of the Congo River. The transition from the still water to the turbulent flow swings the bow downstream and nearly knocks Gardiner into the water. "Almost fell into the drink, eh?" he says with a laugh, though he knows a swim here could be dangerous, even deadly. The Congo is flowing at 1.25 million cubic feet of water per second, enough to fill 13 Olympic-size swimming pools every second. Gardiner, who works for the National Climatic Data Center, in Asheville, North Carolina, is here because he thinks the Lower Congo may contain the deepest point of any river in the world.

We're in Central Africa, 90 miles west of the Democratic Republic of Congo's capital of Kinshasa and about 100 miles east of where the river drains into the Atlantic Ocean, ending its 3,000-mile run across equatorial Africa. A series of grassy hills called the Crystal Mountains rise subtly behind us. Gardiner and John Shelton, a hydrologist from the United States Geologic Survey, are plotting how water moves in such a massive flow. To do this, they brought along an instrument that floats alongside a boat in an orange, plastic vessel about the size of an elementary-school desk. The instrument maps water movement and measures the river's depth. Gardiner tried to accomplish the same thing last year with a device designed for rivers. "The signal petered out well before the bottom," he explains, his hand skimming the river's surface. "So we bought one for oceans."

We're midstream, heading from the north bank to the south, on a course directly perpendicular to the current. If we manage to keep the instrument from being swallowed by one of the 40-foot-wide whirlpools studding the flow, Shelton and Gardiner's work will produce a digital cross section of the river's currents and depth.

The Congo's power—its depth, speed and turbulence—is of particular interest to ichthyologist Melanie Stiassny of the American Museum of Natural History, one of the scientists in our expedition. She studies fish on the lower Congo and over the past decade has discovered six new species (she's working on identifying three more). The number of species known to live in the lower Congo now exceeds 300 and the river contains one of the highest concentrations of "endemism," or species found nowhere else in the world. Stiassny thinks the river's power is shaping evolution in the Congo.

New species evolve when some geographic barrier—a mountain range, an ocean, a glacier—divides a population. Animals on one side of the barrier can no longer breed with animals on the other. Each group adapts to its habitat and, over time, their genes change enough to constitute separate species. This idea dates back to Darwin's Origin of Species, published in November 1859. Stiassny and her colleagues were the first to suggest that there could be barriers within freshwater. Water, after all, is permeable for fish, right?

In 2002, Stiassny and ichthyologist Robert Schelly observed fish that suggested otherwise. They found cichlids, a freshwater fish known to evolve quickly in new environments, on one side of the Congo that were genetically distinct from similar-looking cichlids on the opposite bank. Exceptionally strong currents divided the populations. Though the river was only a mile wide, the habitats were isolated just as if a mountain range had risen between them.

We dock the pirogue on a sandbar. A crowd of locals is thronging around Stiassny. She's holding a mole-like fish that's tiny, blind and to be frank, extremely ugly. Since we arrived in the DRC two weeks ago, Stiassny has been hoping to see this fish.

"Mondeli bureau," says the fisherman who brought it to her, pointing to the fish. Stiassny smiles. The name translates as "white man in an office" and plays on the locals' vision of a computer-bound Westerner: blind, albino, stunted.

Stiassny found a similar specimen covered in gas bubbles during a collecting expedition in 2007. It had suffered from rapid decompression syndrome, or the bends. The apparent cause of death—and the fact that it had no eyes—suggested the fish had evolved in a habitat too deep for light to penetrate.

"Thank you," Stiassny says. "What a beautiful specimen." She lays the fish beside dozens of other specimens on a clear tarp. A graduate student is labeling the samples and storing them in formaldehyde-filled 50-gallon drums to be flown back to New York for genetic testing. The specimens include a 12-pound, prehistoric-looking catfish, its gills still flapping. There are tiny, oval-shaped cichlids colored like the silt, and an eel-like fish that Stiassny thinks may be a new species. The most interesting to me are a half a dozen foot-long fish with long, cylindrical snouts.

"These are elephant fish," Stiassny says. "Their jaws are at the end of their snouts so they can pick food from the gravel."

The evolutionary adaptations are apparent. Each individual was caught in a different location, and each snout is specialized to the character of the river floor in which it fed. Long and thin snouts allow fish to probe for food in deep and small-grained gravel; short and fat snouts allow them to feed on algae-caked bedrock. "Darwin's fishes," Stiassny says.

A series of mud-colored minnows caught in different locations that look identical to me excite Stiassny. "That's really where we see evolution in action," Stiassny says. "In 50 or 100 years, the fish that look the same today may well look different. We can see the start of that genetic drift."

That night, Gardiner plugs a data card in his laptop. Winged insects flock to the glowing screen, their buzzing mostly drowned out by the steady drone of the river and the occasional whoosh of its surge breaking on the beach. The computer hums while processing data. Eventually Gardiner pulls up a graph profiling the river's bed. It looks like a U—as smooth as a mountain valley carved by a glacier. The current just beneath the surface is traveling at 30 miles per hour, and the channel is 640 feet deep.

"That's the deepest point measured on a river in the world," Gardiner says. "There's no question about that."

Shelton is peering over Gardiner's shoulder, shaking his head and deciphering blue and red lines on the computer screen that represent water movement and velocity.

"Just like we thought," he says. "Fabulous stuff." He nudges a moth off the screen and points to a place in the riverbed where a long blue line indicates the current dropping vertically from a ledge into the canyon's trough.

"It's an underwater waterfall," he says, slapping Gardiner's shoulder. It's falling at 40 feet per second. Upstream of the waterfall is an eddy, the water relatively still. This point is likely habitat for the blind cichlid: calm pockets where sheering currents have trapped the fish at great depths. Deep-river specimens, like the one found today, surface only when the river surges and flushes individuals into the harsh environment of the main flow. In terms of Stiassny's hypothesis, the finding suggests that the Congo's currents partition habitat from side to side and from top to bottom—just like a mountain range.

"It shows water can be an evolutionary barrier, even for fish," Gardiner says.


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Our world is so majestic and there is so much we don't know or understand yet.

Posted by zach on August 29,2012 | 01:16 PM

cool

Posted by jonjon on May 7,2012 | 11:35 AM

The coelecanth is a fish found in deep parts of the sea at various locations around the earth. It was fossilized and estimated to be 300 million years old until a living specimen was found off the east coast of South Africa. Here the fish is regarded as being perfectly adapted to its enviroment and worldwide remains unchanged from the fossil. Now this deep water in the Congo River is regarded as an evolutionary pump spewing out all sorts of different fish due to its depth and ability to isolate the various species from one another in different locations who then consequently evolve differently. Scientific question - what is the difference between the deep recesses of the ocean, to produce different evolving species but doesn't, in the above example, but in the shallower river many species do, unfortunately without necessarily having the fossilized evidence to make comparisons.

Posted by Brokenit on May 3,2012 | 08:28 AM

Let's stipulate for a moment that God revealed to Moses everything contained in the Book of Genesis. Moses lived about 1500 BC. What was life like back in 1500 BC?

Well, there was no concept of germs or bacteria or viruses; there were only a handful of known metals--iron, silver, gold, tin, copper; there was no decimal system or concept of ZERO, which means there were no numbers such as million or billion; no such thing as electricity; no knowledge of the speed of light; no certainty as to whether the earth was the center of the universe; no individual gases or radioactivity; no proof of the shape of the planet; etc.

OK, so you're God and you want to tell Moses about creation... but there's this HUGE linguistic barrier to describe lightyears, or genes and chromosomes, or planetary accretion, bloodtypes, continental drift, velociraptors, etc.

Worse than that, you're Moses now, and you actually have a head for science, but your new buddy, God, is helping you flee Egypt with some very extra-scientific tricks: parting the Red Sea, turning a walking stik into a snake, dropping manna from the sky for 40 years, and coming off of Mt. Sinai glowing, to name a few.

Posted by Jimbo on May 31,2011 | 01:48 AM

How did this wonderful article become a playground for close-minded-twits fighting over something SO irrelevant! You should be ashamed over yourself! Leave religion out when it comes to science - and dont try to convience people with strong fundamental beliefs that evolution is a fact- because they will NEVER be open enough to understand! they are still asking "show us the missing link" goddammit- we have them! read some books and go to a museum!
And if there is a God (heaven forbid) He would be so upset with you! Because he would be a scientist himself to create all in this universe and to controll all the fundemantal laws at ones, that if I am wrong, and goes to heaven when I die, He will except me for asking questions and being curious, and not taking the easy-way to the big questions in life...

Posted by Aurora K. on October 13,2010 | 06:18 AM

Evolution and Creation(as explained in the book of Genesis), are completely and absolutely incompatible. Anyone who tries to fit evolution theory into the creation account has not truly studied what God's word says. There is NO agreement! All the questions I see posed by Naturalists in regards to the understanding of the biblical accounts of creation and the flood of Noah leave out the one essential explanation...GOD! The power of the Creator of the universe is not limited by our narrow understanding of His creation and our scientific theories and laws. He is, after all, the Creator of it all!

Posted by Jason G on June 2,2010 | 04:01 PM

Isn't genetic mutation when DNA information is LOST?

Isn't that de-evolution?

For evolution to take place. Wouldn't DNA information have to expand? To ADD?

We don't see any "mutation" adding to DNA anywhere..

Isn't evolution more of a religion? than science?

Posted by Thinker_ on March 25,2010 | 05:45 AM

The human being is the pride of the evolution, but why the hell is this at the same time the unavoidable beginning of the end of the wonderful nature how we know it today?
In a few generations the earth will reach its capacity and then we will understand again that the evolution naturally is a process of selection and not a support of the weak, as we think today...

Posted by weisenheimer on March 23,2010 | 04:33 PM

If there is a God,and he made everything, its must be pretty obvious that he has gone to a huge amount of effort to make evolution a very convincing arguement. Especially for those with a scientific bent of thought and living in the 21st century.

Just a test? No, the obvious answer is that if there is a "GOD", he doesnt want us to believe in him.

Why?, I dont know, but more I see, more I know, longer I live.... more I know I do not believe in a GOD, and if I did believe, and even if I know that GOD exists, I would not go round saying he exists, and trying to persuade others that GOD exists.

And if I did believe, or know GOD exists, I would tell you he doesnt, and you should live your live in the belief That GOD doesnt exist.

Regards John A

Posted by john on March 21,2010 | 08:30 AM

It might be enlightening if more people would study the meanings of words like "Theory", "Scientific Theory", "fact", "evolution", "faith","Christian", and many others typically used in these discussions. At the core of many disagreements is the assumption that we all embrace equal definitions of these words; we do not. A good place for most of us to start would be to understand our own definitions for the words used in these discussions, and then explore others' definitions.

Posted by Jamie on February 13,2010 | 11:09 PM

I believe in God. I also believe in evolution.
Man was created in God's image. My guess is that after planting the seeds of life on this planet, he let life evolve, then took a primitive being, a Neanderthal or Cro-Magnon or whatever, mixed his or his angels DNA with it and created Man.

If you believe in the what the bible says then we know that human and angel DNA is compatible. The angels who disobeyed God and came down to earth before the great flood had relations with human women and had hybrid children called Nephilim. This in itself is an act of a species evolving.

Who is God but a superior being?
The truth lies somewhere between evolution and creation. After all, plenty of lifeforms including dinosaurs and upright walking bipeds did exist before intelligent Man. This is a fact. Where did they come from? Were they put here by a superior being, or did they evolve? or both?

If you believe in that God can do anything. He's the greatest scientist of all time, and could have created life with the capacity to evolve. Not so hard to grasp is it?

Posted by Eral on December 25,2009 | 12:27 AM

Re: the St. Lawrence and "Dean."

The reference here is to freshwater rivers well above any influence of the tide. If you have evidence of a 1,000 foot hole in the Sanguenay above tidal influence, then you should publish a paper on it. Or the better question is, why haven't you?

---
Martin: ("Canada has innumerable fresh water lakes that are land locked from any other lake for centuries. Why is a walleye a walleye and a northern pike a northern pike in everyone of them? Sure, the fish could be "evolving" in the Congo, but there could also have been a gazillion species to start with, and they are just being discovered BECAUSE the water is so deep and swift.")

You didn't read the story. Speciation occurs due to geographic separation which prevents interbreeding over time. In a Canadian lake, walleye and pike from any part of the lake can breed with each other, and do. Nothing is stopping them. In the lower Congo the situation is exactly the opposite, which is sort of the point of the whole story.

Posted by Douglas Watts on December 22,2009 | 02:05 AM

Evolution is one of God's greatest hoaxes! Sorry, it seemed funny at the time.

Thank you for the wonderful article. I am glad that someone other than me ponders such subjects. I would have loved to see some of the fishes also.....maybe in a future publication?

Posted by Paul on December 15,2009 | 01:10 PM

Obviously evolution exists, otherwise we'd all have the exact same adaptations (for example, some of the Asian culture have evolved away the ability to proccess alchohol correctly). It's not a question of whether it's a lie, it's a question of whether God is involved in any way, and that's an opinion, not a fact.

Very interesting article, though I would have loved to see some of the fish. :(

Posted by Ellen W. on November 28,2009 | 09:18 AM



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