Does evolution ever go backward?
In regressive evolution, organisms lose complex features and can appear to evolve "in reverse." But evolution doesn't retrace its steps, experts said.
Evolution has produced stunningly complex features, from neuron-studded octopus arms to the mammalian ear. Can evolution ever go "backward," though, reverting complex creatures to previous, simpler forms?
In so-called regressive evolution, organisms can lose complex features and thus appear to have evolved "back" into simpler forms. But evolution doesn't really go backward in the sense of retracing evolutionary steps, experts say.
"The chances that the same tape [of evolutionary changes] would be … reversed in the same way is highly improbable," William R. Jeffery, a biologist at the University of Maryland, told Live Science.
Regressive evolution involves the loss of previously evolved forms of complexity, Beth Okamura, a life sciences researcher at the Natural History Museum in London, told Live Science. An extreme example comes from the myxozoans, parasites with very simple anatomies — no mouths, nervous systems or guts — and very small genomes. The simplest type "are essentially single cells," Okamura said.
Long classified as single-celled protozoans, myxozoans eventually revealed themselves to be highly regressed animals, Okamura said. They evolved from cnidarians, a group that includes jellyfish, losing many features no longer needed in a parasitic lifestyle.
Thus, myxozoans may seem, at least morphologically, to have returned to a previous evolutionary stage, Okamura said. "They're sort of converging on single-celled organisms," she said.
Related: How long do new species take to evolve?
Still, the evolutionary process doesn't retrace its steps in regressive evolution, Jeffery said. Cave-dwelling creatures also frequently undergo regressive evolution, losing complex features, like eyes, that are not needed in dark environments. But eye loss in cave fish, for example, doesn't mean an exact return to a primordial ancestor without these organs, Jeffery said. Instead, processes that previously produced the eye stop partway through, leaving a vestigial eye overgrown with skin.
"Things can look like they're going into reverse," Jeffery said. "But the eye didn't go in reverse. It just stopped going forward."
Additionally, losses in complexity may accompany less-obvious increases in complexity, such as the biochemistries parasites use to get inside hosts, Okamura said. "It's very easy for people … to think of evolution in terms of what you see … what the morphological features are," she said. "But there are also lots of other features that we don't see at the physiological and the biochemical level."
In cave fish, lost eyes may similarly obscure alternative complexity. Organs responsive to vibrations appear in great quantities in these fish, providing a way to sense in dark environments. And in the already-overstuffed head, these organs found available real estate in the fish's empty eye sockets, Jeffery said.
Backtracking through complexity
Part of the reason evolution doesn't retrace its steps is that adaptations lead to other changes, Brian Golding, a biologist at McMaster University in Ontario, told Live Science. That makes simply dialing back a specific change extremely complicated.
"If you've made a change … you're going to fine-tune that adaptation, and that adaptation will interact with other genes," Golding said. "Now, if you reverse that one change, all of the other genes are still going to have to be changed" to reverse evolution.
In cave fish, for example, the original development of an eye may have come with changes not only to proteins needed for eyes but also to skull structures of an eye socket. A mutation affecting an eye protein wouldn't cause an organism to revert to one without the socket.
Finally, experts cautioned that the term "backward evolution" may imply, misleadingly, that evolution has a goal of creating more complex forms. However, evolution merely favors features that make an organism more fit for a particular environment, Okamura said.
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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Michael Dhar is a science editor and writer based in Chicago. He has an MS in bioinformatics from NYU Tandon School of Engineering, an MA in English literature from Columbia University and a BA in English from the University of Iowa. He has written about health and science for Live Science, Scientific American, Space.com, The Fix, Earth.com and others and has edited for the American Medical Association and other organizations.
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I now believe there is an evolution of human endeavors culminating in what we see currently and that is the unsustainable goals of this present administration and their ilk. This debacle began approx. six decades ago and matured into what we are experiencing now.
It may be a degrading of humankind's genome left unchecked for too long. Now the toxicity of a progressed Marxist entity reveals what we have allowed to grow and rule America.
Much deeper than we are able to remedy. The cause lies beyond our ability to correctly recognize what we are struggling against. In this fashion of resistance, I see there is no way out. Our unnatural state will not allow the natural response of purging the proven destructive pathogen now threatening societies.
Reverse evolution is a rational theory but is in effect substantiated by an observation of ancient civilizations having gone through what we are experiencing. In every major society there comes the same generation completely irrational in their unsustainable views and bold in confrontation. America and the world are in this state mainly coming from a young generation basically lost and estranged from reality and predictable in weakening any populace allowing their degeneration to the point of endangering the entire sustainable society.
God created the heavens and the earth and His proof is displayed every moment by looking upon His creation. Adam and Eve sinned and as a result the fallen world became what it is. Through Christ it will be restored. The Bible is the true Word of God.
You, Frank F. are a rare individual whose mind can except a wildly rational posit. Fascinating to examine whether this current world debacle, which appears to have evolved to toxic proportions over six decades, has appeared in history and records, letters, among many sources, and how they experienced true downfall from exactly what we are going through now in their own fashion.
The weakening always originates from the generation who didn't have the responsibilities and toil as the former did. The same deterioration took place as now by substandard individuals conducting themselves and saying things much as currently, only in a different way.
There is no remedy for the world's plight. It's not a matter of politics, perversion, or even the deep state's diabolical designs. It is something we have no control over, and worldwide tumult is only an indicator of degeneration snowballing.
Our technology is outpacing us. As we experience this perhaps twilight of humankind, the things we have created will be our destroyers. Technology is rising while humans are declining. Even a glimpse of human character seals the posit.
This is not going away, in fact perplexity is setting in and we are finally cornered in tribulation which was recoverable in the past. As I mentioned, the maturation of seeded ills sixty years ago has provided the current and perpetual dead end to humankind.
This generation I speak of gives nothing to the sustainability of their society, instead like the leftist plague attacking us now, they become aggressive in insisting their voices be heard. The decay of their nation comes rather slow but ends decisively, every time. A disposable generation.
The result is what's happening currently with the incremental dissolution of America and the western nations. So, in summation I view human civilizations as entropic in their evolution and termination. It begins at conception of a civilization and digresses to their demise as a society, Like a ticking clock .
I believe humankind is not natural to this world and it has created all our ills. The curse of a short life and an unnatural environment promotes situations not producing a sustainable existence for us. What would a species such as us do when introduced to an environment below our natural state? Dominating and twisting the natural world to our requirements continuing to this moment. There's nothing natural about humankind.
That's my rant for this beautiful Wednesday. Happy novel research.