Darwin evolution going backwards? Not really (Introduction)

by David Turell , Tuesday, January 17, 2023, 16:03 (465 days ago) @ David Turell

Loss of function is an adaptation to loss of need:

https://www.livescience.com/regressive-backward-evolution?utm_term=C3CFD69C-A485-4C10-9...

"In regressive evolution, organisms lose complex features and can appear to evolve "in reverse." But evolution doesn't retrace its steps, experts said.

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"Regressive evolution involves the loss of previously evolved forms of complexity, Beth Okamura(opens in new tab), 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.

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"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.

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"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."

Comment: I believe this is a Darwinian by reasonable point of view.