Does evolution ever go backward?

Does evolution ever go backward?

Regressive evolution causes creatures to lose complicated traits and can make it seem like evolution is going “backwards.” But according to specialists, evolution doesn’t go backwards in time.

From the neuron-studded octopus limbs to the mammalian ear, evolution has created amazingly intricate characteristics. But can evolution ever “go backward,” returning complicated beings to earlier, more basic forms?

Organisms may lose complicated characteristics during a process known as “regressive evolution,” giving the impression that they have “evolved back” into simpler forms. However, according to specialists, evolution doesn’t actually go backward in the sense of retracing evolutionary stages.

According to William R. Jeffery, a biologist at the University of Maryland, it is extremely unlikely that the same recording [of evolutionary changes] would be reversed in the same manner.

Losing complexity

According to Beth Okamura(opens in new tab), a life sciences scholar at the Natural History Museum in London, regressive evolution includes the loss of previously developed types of complexity. The myxozoans, parasites with extremely basic anatomy that lacks mouths, nerve systems, or intestines, provide an extreme illustration. The simplest kind “are basically single cells,” according to Okamura.

Myxozoans, which were previously thought of as single-celled protozoans, ultimately showed that they were actually very regressed mammals, according to Okamura. They descended from jellyfish and other cnidarians, shedding many characteristics that were no longer necessary for their parasitic existence.

Myxozoans may therefore appear to have transitioned back to an earlier developmental stage, at least visually, according to Okamura. They are essentially resembling single-celled creatures, she claimed. According to Okamura, this suggests that myxozoans may look to have returned to a previous developmental stage, at least aesthetically. She asserted that they basically resemble single-celled organisms.

However, in regressive evolution, the genetic process does not go backwards, according to Jeffery. Additionally, cave dwellers frequently experience regressive evolution, shedding intricate characteristics like eyeballs that are unnecessary in the dark. However, the absence of these structures in cave fish, for instance, does not necessarily indicate a precise return to a primitive progenitor, according to Jeffery. Instead, processes that once created the eye halt midway through production, leaving a vestige of an eye covered in skin.

Things sometimes appear to be moving backward, according to Jeffery. “However, the eye didn’t turn around. Simply put, it halted moving forward. According to Jeffery, sometimes it seems as though things are going backward. The eye didn’t swivel around, though. It simply stopped going forward.

Furthermore, Okamura noted that losses in complexity could coexist with less apparent gains in complexity, such as the biochemistries parasites employ to enter their hosts. According to her, “it’s very simple for people to conceive of evolution in terms of what you see… what the morphological characteristics are. However, there are a ton of additional characteristics that are not visible at the metabolic and molecular levels.

Lost eyes can similarly conceal different intricacy in cave fish. These fish have a large number of vibration-responsive organs, which allow them to detect in low-light conditions. These organs also found space in the already crammed cranium in the fish’s empty eye sockets, according to Jeffery. Similar to how lost irises can mask varying complexity in cave fish. These fish are able to sense in dim light because of their numerous vibration-responsive organs. According to Jeffery, these innards also managed to fit into the fish’s already overstuffed skull and the empty eye sockets.

Backtracking through complexity

According to Brian Golding(opens in new browser), a scientist at McMaster University in Ontario, one of the reasons evolution doesn’t go back in time is that adaptations result in other changes. That makes it very difficult to merely roll back a particular change.

If you make a modification, your adaptation will be fine-tuned and communicate with other genes, according to Golding. In order to stop evolution, all of the other DNA would still need to be altered, even if just that one change were to be undone.

For instance, in cave fish, alterations to the structures of the eye socket in the cranium as well as the proteins required for eyes may have occurred during the initial growth of an eye. An creature wouldn’t return to one without the socket due to a mutation impacting an eye protein.

Finally, experts issued a warning that the phrase “backward evolution” may falsely suggest that the purpose of evolution is to produce more complicated forms. According to Okamura, evolution simply promotes traits that make an organism better suited for a specific habitat.

In this way, regressive evolution is just evolution as usual. Losing complexity may make a parasite or cave dweller better adapted to its new environment — for example, by eliminating the energy costs of making a complex organ, Jeffery said. 

“Evolution is always progressive in that it’s selecting for features that improve the fitness of the individuals in which that variation is being expressed,” Okamura said.

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