A TikTok video about Typhlichthys styx, a blind cave fish found in the southeastern United States, is attracting attention after social media creator and middle school science teacher @zekedarwinscience explained new findings could challenge part of Charles Darwin's thinking about life underground.
In the video, the creator described the discovery as "evolution in the underworld," arguing that it points to cave ecosystems being more dynamic than Darwin once believed. Rather than serving as evolutionary dead ends, these environments may continue to generate new species and adaptations over long periods of time.
@zekedarwinscience Evolution in the Underwold and a new cave fish species that proves evolution is more nuanced than Darwin realized (and that's okay… Darwin lived in the 1800s) | Typhlichthys styx #animals #fish #evolution #biology #learnontiktok ♬ original sound - Zeke Darwin
Typhlichthys styx lives in cave systems under parts of Tennessee, Alabama, and Georgia.
Scientists were already aware of the species of blind cave fish, and others like it, but a closer genetic analysis changed the picture: fish from populations that looked alike turned out to be far more distantly related than researchers had assumed.
The creator explained that new DNA data indicate these lineages began separating about 8 million years ago.
The video also featured CT scans created by researchers, revealing subtle anatomical differences between populations that helped scientists identify them as distinct groups.
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Researchers first compared the fishes' distributions with maps of surface waterways, but those patterns did not fully explain where the different populations were found. When they added underground aquifer systems to the analysis, however, a clearer picture emerged.
As the creator put it, a "hidden highway" appeared — a network of subsurface waterways that may have allowed the fish to spread underground for millions of years before becoming isolated, eventually evolving into separate species.
The result complicates a classic Darwinian idea. The TikTok creator explained that Darwin had treated caves as mostly one-way evolutionary paths, places where organisms could enter, adapt to perpetual darkness, lose features like eyes and pigmentation, and ultimately end that branch of the lineage.
The study discussed in the video suggests cave evolution can, in rare cases, play out differently. Here, subterranean populations seem to have continued branching off.
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