Does Evolution Go Backwards? Curious Scientists Try Unlock the Mystery

Regressive evolution causes animals to lose sophisticated traits and might make it seem like evolution is going "backward." But according to specialists, evolution goes forward in time.

human evolution — Johannes Plenio/Unsplash

Does Evolution Move Backward

Evolution has evolved amazingly complex traits from the neuron-studded octopus arms to the human ear. But can evolution ever "go backward," returning sophisticated beings to earlier, more basic forms?

Organisms may lose complex traits via a process known as "regressive evolution," giving the impression that they have "evolved back" into simpler forms. However, according to specialists, evolution goes forward in retracing evolutionary stages, as per NCBI.

According to William R. Jeffery, a scientist at the University of Maryland, "it is exceedingly implausible that the same tape [of evolutionary changes] would be... reversed in the same manner."

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A Complex and Intricate Process

According to Beth Okamura(opens in new tab), a biosciences researcher at the Natural History Museum in London, regressive evolution includes the loss of previously developed forms of complexity. The myxozoans, parasites with fundamental anatomy that lacks mouths, nervous systems, or stomachs, provide an extreme example. The simplest kind "are basically single cells," according to Okamura.

Myxozoans, previously thought to be single-celled protozoans, later showed that they were very backward creatures, according to Okamura. They descended from jellyfish and other cnidarians, shedding several characteristics that were no longer necessary for their parasitic existence.

Myxozoans may have transitioned back to an earlier evolutionary stage, at least morphologically, according to Live Science. She said that they were "kind of convergent on single-celled creatures."

However, in regressive evolution, the evolutionary process goes forward, according to Jeffery. Additionally, cave dwellers usually experience regressive evolution, losing complex traits like eyes that are unnecessary in the dark. However, the absence of these organs in cave fish, for instance, does not always indicate a precise return to a primitive progenitor, according to Jeffery. Instead, mechanisms that formerly generated the eye halt midway through production, leaving a vestige of an eye covered in skin.

Furthermore, Okamura noted that losses in complexity might coexist with less visible gains in complexity, such as the biochemistries parasites use to enter their hosts. According to her, "it's straightforward for people to conceive about evolution in terms of what you see... what the morphological traits are. However, there are a ton of other characteristics that need to be visible at the physiological and biochemical levels.

Lost eyes may also conceal alternate complexity in cave fish. These fish have many vibration-responsive organs, which allow them to perceive in low-light conditions. According to Jeffery, these organs also found space in the already crammed skull in the fish's vacant eye sockets.

According to Brian Golding(opens in new tab), a scientist from McMaster University in Ontario, evolution doesn't go back in time because adaptations result in other modifications. That makes it very difficult to roll back a particular change.

If you modify, your adaptation will be fine-tuned and interact with other genes, according to Golding. All of the other genes would still need to be altered to stop evolution, even if only that one mutation were to be undone.

In cave fish, for example, the initial creation of an eye may have occurred with alterations not just to proteins essential for eyes but also to skull components of an eye socket. An organism wouldn't return to one without the socket due to a mutation affecting an eye protein.

May Cause Some Misinformation

Finally, scientists warned that the phrase "backward evolution" may falsely indicate that the purpose of evolution is to produce more complex organisms. According to Okamura, evolution promotes traits that make an organism more suited for a certain environment.

Regressive evolution is, therefore, just evolution as normal. According to Jeffery, a parasite or cave dweller may become more acclimated to its new habitat by losing complexity; for instance, by saving the energy required to create a complex organ.

Okamura states, "Evolution is always progressive in that it selects for traits that enhance the fitness of the individuals in whom that variation is exhibited."