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In an Evolutionary Transition from Sea to Land, the Real Challenge May Be “Drying Out”

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Researchers at the University of New South Wales have published in the journal Evolution, documenting something we kind of already knew: some fish can spend considerable time out of water, not only surviving but thriving (“Repeated evolution of amphibious behavior in fish and its implications for the colonisation of novel environments“).

The interest is supposed to lie in demonstrating the ease with which sea dwellers could have made the evolutionary transition to land, with the burden of breathing outside of water. From the write-up at Science Daily:

Fish have evolved the ability to live on land many times, challenging the perception that this extreme lifestyle shift was likely to have been a rare occurrence in ancient times, new UNSW Australia research shows.

“A fish out of water might seem an extraordinary thing, but in fact it is quite a common phenomenon,” says study first author and UNSW evolutionary ecologist Dr Terry Ord. “Amphibious behaviour has evolved repeatedly in a wide diversity of present day fish, and the move onto land does not appear to be as difficult as has been presumed.”

The emergence of fish onto land more than 350 million years ago was a critical step in the history of life on Earth, leading to the evolution of all land vertebrates, including humans.

Or as the Abstract puts it in slightly more technical language:

We know little about on how frequently transitions into new habitats occur, especially the colonisation of novel environments that are the most likely to instigate adaptive evolution. One of the most extreme ecological transitions has been the shift in habitat associated with the move from water to land by amphibious fish. We provide the first phylogenetic investigation of these transitions for living fish. Thirty-three families have species reported to be amphibious and these are likely independent evolutionary origins of fish emerging onto land. Phylogenetic reconstructions of closely related taxa within one of these families, the Blenniidae, inferred as many as seven convergences on a highly amphibious lifestyle. Taken together, there appear to be few constraints on fish emerging onto land given amphibious behavior has evolved repeatedly many times across ecologically diverse families. The colonisation of novel habitats by other taxa resulting in less dramatic changes in environment should be equally, if not, more frequent in nature, providing an important pre-requisite for subsequent adaptive differentiation.

The scientists studied blennies, and you can see a video of them doing their thing here:

Confirmed: those are land-going fish.

“In this one family of fish alone, an amphibious lifestyle appears to have evolved repeatedly, between three and seven times,” says Dr Ord.

A snap, right? Is it a triumph for evolutionary theory? Biologist Ann Gauger addressed a “walking” fish here a little while back:

Some of the skeletal differences reflect those expected for a water to land transition. I’d like to compare it to other fish that move on land, like mudskippers.

[T]he spine, ribs and pelvic girdle may have been an adaptation as a result of the stresses of climbing and walking. But wait. I thought the phenotypic change had to come first in order to be adaptive. Random mutation, leading to the development of the spine and pelvic girdle, would then fortuitously allowed the fish to walk, and allow for its selection as a beneficial trait or traits.

It’s an intriguing find. Does this fish disprove intelligent design? No. There is nothing in the theory of intelligent design that necessarily rules out common descent, so this fish could be a relic of the transition to land, and it would not matter.

If fish made an evolutionary move to land, as ID is perfectly willing to entertain, then a “relic” or “relics” could well exist. That doesn’t mean the move could occur in the absence of purposeful direction, taking into account the “adaptational package” it would seem to require — the “set of structures that are carefully coordinated with one another to help the organism make a living,” as Dembski and Wells put it in The Design of Life.

Dr. Gauger mentions mudskippers, as does the news from UNSW. Here’s a charming, almost adorable brief documentary on these even more impressive fish and their lifestyle.

Breathing on land per se isn’t necessarily the biggest problem for fish out of water. It’s a problem, but the larger hurdle may be overcoming the peril of “drying out.” Mudskippers and blennies alike have to take care about that. Dr. Ord again:

“The real difficulty in developing a fully-fledged terrestrial lifestyle may be in preventing drying out. This has direct consequences for them breathing on land because they still require their gills, which need to stay moist to function properly.”

Ohhh. This admission comes at the end of the news item about how readily fish evolve and adapt to dry land. Now they tell us.

Photo credit: Georgina Cooke, University of New South Wales, via Eureka Alert.

David Klinghoffer

Senior Fellow and Editor, Evolution News
David Klinghoffer is a Senior Fellow at Discovery Institute and the editor of Evolution News & Science Today, the daily voice of Discovery Institute’s Center for Science & Culture, reporting on intelligent design, evolution, and the intersection of science and culture. Klinghoffer is also the author of six books, a former senior editor and literary editor at National Review magazine, and has written for the Los Angeles Times, New York Times, Wall Street Journal, Washington Post, Seattle Times, Commentary, and other publications. Born in Santa Monica, California, he graduated from Brown University in 1987 with an A.B. magna cum laude in comparative literature and religious studies. David lives near Seattle, Washington, with his wife and children.

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