Selected Carp Devolved Rapidly to Wild Type

Artificial selection isn’t forever. Some fish reverted to their old ways.

When monks “evolved” fish to have fewer scales so that they were easier to prepare for food, they had created a new species, it was thought. The “mirror carp” were popular in restaurants. Since Madagascar didn’t have carp, someone thought it would be great to introduce them there, so that the locals could improve their seafood cuisine. It didn’t last, PhysOrg says. Bob Yirka’s headline reads, “Carp demonstrate rapid de-evolution to get their scales back.”

The program was considered a success as the fish flourished in the new environment. It did not take long for the breeding process to begin reversing itself, however—as early as 1950, people in the area were reporting that the carp were becoming scalier. In this new effort, the researchers sought to better understand the evolutionary process that the fish have been undergoing over the course of the past century.

The study consisted of capturing approximately 700 specimens in Madagascar and analyzing both their scales and DNA. In studying their results, the researchers found that approximately 65 percent of those they caught were fully scaled—back to where they had been before the monks got involved.

An interesting aspect of the reversal, however, is that the old genes for scaliness didn’t return. The genes changed by the monks were still present.

But surprisingly, they also found that the new scales were not the result of reversing the DNA changes that had occurred during the time they were bred to have fewer scales—those gene changes were still present, which suggested that different genes were involved in rescaling.  This meant that the fish had evolved back to its original form over the course of just 100 years, which translated to approximately 40 generations—a mere blip in general evolutionary terms.

The researchers believe the fish devolved back to its original form because scales offer better protection against parasites and predators.

Obviously, the fish did not get together and decide to grow scales for better protection. It happened naturally somehow. But if this were a law of nature, why don’t all fish in the sea get scalier over time? Another explanation might lie in the observation that each species has its own norm. Perturbations away from that norm can be sustained temporarily, but tend to revert when artificial constraints are lifted.

Notice that the carp are still carp, the scales are still scales, and the direction of evolution was backward. That’s why they call it de-evolution. There’s no sense carping on this as an example of Darwinian evolution. The monks perturbed these fish away from their norm. Genes are not the drivers of the norm, but effects of the norm. Epigenetic effects and gene networks can store the information for scaliness in different locations from those of the original European wild-type carp. When the experiment was over, in a short time, the carp went back to their old ways. When you are sold a fish story that a study helps “to better understand the evolutionary process,” carpe deum.