Scientists Find Evolution Can Be Reversible

It turns out that evolution can go in reverse.

A peculiar ant species discovered by scientists has shown that evolution as we know it can be reversible.

The size and shape of the head of a variety of soldier ants have revealed that evolution can be reversible. In other words, the ant species is evidence that evolution can progress in reverse.

Turtle soldier ants look like real-life creatures straight out of a Japanese anime movie.

These tree-dwelling insects glide back and forth sporting oversized, shiny heads, which they use to block the entrances of their nests, essentially acting as live gates.

However, scientists have found that three’s diversity among them, and that not all heads are the same shape: some ants were found having covers and perfectly seal tunnel entrances. Others have square heads, which they assemble into multi-member locks reminiscent of the overlapping shields of a Spartan army.

This variety of head shapes reveals more than just one of nature’s strange quirks: It can also shed light on how species evolve to fill ecological niches.

And that evolution, as new research published in the Proceedings of the National Academy of Sciences (PNAS) shows, is not always a one-way street toward greater evolution. Occasionally, it can take a species to a more general stage. In other words, it can cause a species to de-evolve.

“Usually, you would think that once a species is specialized, it’s stuck in that very narrow niche,” revealed in a statement Daniel Kronauer, head of Rockefeller’s Laboratory of Social Evolution and Behavior. “But turtle ants are an interesting case of a very dynamic evolutionary trajectory, with a lot of back and forth.”

Similar to many other social insects that live in colonies, turtle ants are known to specialize in different functions, often developing exaggerated characteristics suitable for their work. For soldiers, this process has resulted in large heads that come in a variety of shapes. These odd-looking heads serve as protective colonial shields.

The lead author of the study, Scott Powell, a biologist at George Washington University explains that “there’s a whopping four-fold difference between the smallest and largest turtle ant soldier heads.”

To better understand this, Powell explains that we ought to picture the smallest species being able to comfortably sit on the head of the largest species.

The new study explains that the shape and size of the head of a soldier turtle ant is directly dictated by the type of tunnel the species in question occupies.

The ants do not dig the tunnels but move to those that have been excavated hitching a ride.

And since a down tunnel could be too big or too small, ants quickly diversify to fill it, the scientists explained.

The relationship between turtle ant heads and tunnels can, therefore, offer a unique and clear view of natural selection.

Researchers can easily compare a trait—head circumference—with the ecological feature it’s evolved to adapt to the nest-entrance size, scientists have explained.

As Kronauer says, “It’s a 1:1 match on the exact same scale.”

The Rockefeller University
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