Some Fish Still Walk on Land: an Evolutionary Throwback

We've all seen Hollywood's rendition of evolution on fast-forward. A fish flops out of a young Earth's primordial sludge and suddenly starts crawling forward on lengthening fins. Suddenly a frog-like creature is before us and it's making headway into thick grasses. Between thickening brown blades, we see the creature change more. Soon enough it's standing upright and long digits curl around a nearby stone.

Fast forward some more and that stone is now the handle of a briefcase and matted hair is replaced by a finely tailored suit. There we have modern man, looking out over a sparkling and sprawling metropolis where once there was nothing but sludge.

It's a very romantic idea, but on a very basic level, it's exactly what evolutionary theorists believe happened. Now, researchers are looking at one kind of fish that seems to have been left back a long way, never getting quite past just crawling in the mud.

Bichir fish (Polypterus) are native to Africa's Nile basin, and are considered the closest living relatives to the predecessors of tetrapods - land-roaming animals such as amphibians, reptiles, mammals, and possibly even birds.

These remarkable fish have a set of lungs alongside functioning gills, and can even crawl across land when they must, looking remarkably like Hollywood's rendition of the first land-life.
[Credit: Standen/doi:10.1038/nature13708]

Researcher Emily Standen wanted to see why exactly these fish stayed the way they did, and if their "walking" could even improve if forced to stay on solid land.

According to her observations, published in the journal Nature, Standen's stranded Bichir fish delivered on her hypothesis and then some.

"The anatomy of the fish raised on land changed, and those changes reflected what we see in the fossil record in the transition from fish to four-legged terrestrial vertebrates," she excitedly told New Scientist.

According to the study, the 100 or so Polypterus that were raised on land quickly learned to raise their heads higher and more securely plant their fins on the ground to maintain stable walking, compared to a control group raised in a standard aquarium.

Their bone structure was even seen to change over time, with shoulder blades growing slightly longer than average and what appeared to be the slow development of a neck among the land-raised.

Still, Standen points out that this was a mere generation of the difficult-to-raise fish, and more work will need to be done to see if these observed changes persist over time.